PatentDe  


Dokumentenidentifikation EP0687207 01.02.1996
EP-Veröffentlichungsnummer 0687207
Titel VERBESSERTE SPANNZANGE UND METHODE ZUM OPTIMIEREN IHRER GREIFAKTION
Anmelder Power Tool Holders Inc., Wilmington, Del., US
Erfinder KANAAN, Roger, J., Easley, SC 29640, US
Vertreter derzeit kein Vertreter bestellt
Vertragsstaaten AT, BE, CH, DE, ES, FR, GB, GR, IE, IT, LI, SE
Sprache des Dokument En
EP-Anmeldetag 04.01.1995
EP-Aktenzeichen 959079898
WO-Anmeldetag 04.01.1995
PCT-Aktenzeichen US9500160
WO-Veröffentlichungsnummer 9518690
WO-Veröffentlichungsdatum 13.07.1995
EP-Offenlegungsdatum 20.12.1995
Veröffentlichungstag im Patentblatt 01.02.1996
IPC-Hauptklasse B23B 3/20

Beschreibung[en]
BACKGROUND OF THE INVENTION

The present invention relates to a method to design a machine tool collet of the kind described in the preamble of claim 1. More particularly it is directed to a method of optimizing the collet parameters in order to maximize gripping strength.

U.S. Patent No. 2,346,706 to Stoner and assigned to the Jacobs Manufacturing Company describes a collet having a plurality of flat-sided gripping members. The gripping members are held in relative position equally spaced about a common axis. The spaces between the gripping members are filled with an adherent resilient material, such as rubber or rubber composition. The gripping members are also transversely perforated. In this case, the resilient rubber material not only fills the space between adjacent gripping members, but it also passes through the perforations in the gripping members thereby forming a plurality of longitudinally spaced continuous annular rings which hold the gripping members in desired relative positions. This collet was a significant improvement over the conventional split steel collets and is widely recognized today by those skilled in the art and commonly known as the Rubber-Flex® collet. However, prior to applicant's present invention, it was not known to optimize the gripping strength of the Rubber-Flex® collet by determining optimum design parameters for the gripping blades or "jaws." Although a number of jaws having varying thicknesses were utilized in the collets, it was not commonly believed that gripping strength could be maximized by deducing the optimum number of gripping jaws for a given configuration which would fit around the inner diameter of the collet while maintaining at least a minimum amount of the resilient material between the gripping jaws. Additionally, the thickness of the gripping jaws was generally not considered as effecting gripping strength. Typically, the jaw thickness was dictated by the size or inside diameter of the collet. In other words, smaller diameter collets had thinner jaw blades.

U.S. Patent No. 5,123,663 to Mizoguchi discloses a method for determining the minimum number of segments for a metal collet by determining the range of a central angle (theta) where the geometrical moment of inertia for each segment is constant with respect to a line passing through the centroid of the section perpendicular to a radial direction of the collet. The patent discloses that the range of angle theta is less than 30° regardless of the thickness of the segment. Once the central angle of about 30° is attained, any further increase in the number of segments will only increase the number of manufacturing steps and lower the tensile strength a cylindrical portion of the collet.

In the document "Jacobs presents Rubber-Flex - the new generation of collet chucks for toolholding", which corresponds to the preamble of claim 1 collets are described which have a greater range than any split steel collets on the market. The Jacobs Rubber-Flex collet system uses two-thirds fewer collets than conventional split steel collet systems. There are different collet series described which have different numbers of steel inserts in the Rubber-Flex collet. It is shown that because of the unique construction of the Jacobs Rubber-Flex collet there are several advantages, as preventing the collet and tool from sticking in the chuck during tool changes or resistance to heat and to all commonly used cutting fluids. In this document there is no information about how to design Rubber-Flex collets to get an improved maximum total torque and to get a wider range of the capacity of the collet. There is also no information about the parameters, which have to be considered when designing such an improved collet.

OBJECTS AND SUMMARY OF THE INVENTION

It is a principle object of the present invention to provide a method to design a machine tool collet of the type having independent gripping jaws molded in a rubber composition, whereby the gripping strength of the collet is maximized.

It is also an object of the present invention to provide method of design of a collet having an optimized gripping strength which is compatible to conventional collet sizes and requirements and interchangeable with conventional split steel collets.

Yet a further object of the present invention is to provide a method for determining the ideal gripping jaw thickness and number of jaws to optimize the gripping strength of a collet design.

Still a further object of the present invention is to provide a design optimization method for optimizing the design of a collet and which may be utilized on a personal computer.

And yet another object of the present invention is to provide a method for predicting collet torque slippage useful for maximizing a collet design.

It is also an object of the present invention to provide a collet torque slippage analysis method for determining the optimum characteristics or design parameters for a collet of specific dimensions and requirements.

Yet a further object of the present invention is to provide a collet torque slippage analysis method for determining the optimum parameters for the gripping jaws within the collet for a collet of conventional dimensions and requirements.

And still a further object of the present invention is to provide an analysis method for improving the gripping strength of the wide variety and sizes of conventional collets.

And yet another object of the present invention is to provide an analysis method for determining maximum collet torque for a collet configuration having predetermined design parameters, the method being useful in optimizing design parameters of the collet.

Still a further, object of the present invention is to provide a method for optimizing collet design parameters, the method being useful in predicting optimum collet parameters to maximize gripping strength of the collet.

It is also an object of the present invention to provide method of design of a machine tool collet wherein at least one of the structural dimensions or characteristics of the gripping jaws of the collet is optimized for maximizing the gripping strength of the collet.

Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. To achieve the objects and in accordance with the purpose of the invention, as embodied and broadly described herein, a method is provided according to the features of claim 1. The method according to the invention comprises the steps of determining the radial force of the gripping jaws upon a bar disposed through the collet, the radial force being dependent upon an axial force applied to the collet, and determining the torque developed on the bar from the radial forces of the gripping jaws just prior to a toggle condition occurring between the gripping jaws and the bar. The method further calls for determining the total moment force generated between the gripping jaws and the bar at toggle condition for a given toggle angle. According to the method of the invention, the toggle angle is varied until the total moment force between the gripping jaws and bar at toggle condition reaches a maximum value. The method further calls for determining the total torque on the bar from the torque prior to toggle and the maximum total moment force at toggle condition.

By employing the method of the present invention, an optimum design for a given collet configuration can be determined by varying parameters of the collet design and determining the total torque on the bar until a maximum torque value is determined for a given collet configuration.

The present method may be utilized in determining the optimum design for all known collet configurations, including the ER and TG collet configurations.

In a preferred embodiment of the method according to the present invention, the method includes the step of varying the thickness of the gripping jaws for a given collet configuration to determine the thickness of gripping jaw generating maximum total torque for a given collet configuration. Likewise, the method may include the step of varying the number of collet jaws for a given collet configuration to determine the number of gripping jaws generating maximum total torque for a given collet configuration. The method may further include the step of varying the jaw material, for example from steel to plastic, to determine the optimum material for maximizing gripping strength.

In further accordance with the purpose of the present invention, a method is provided for determining the optimum design for a given collet configuration and comprises the step of calculating the total torque generated on a bar passing through the collet of a given collet configuration having predetermined design parameters, the total torque including torque generated just prior to toggle occurring between the gripping jaws and the bar and the maximum moment force generated between the gripping jaws and the bar due to toggle. The method also calls for varying at least one design parameter of the collet and recalculating the total torque generated until the total torque generated reaches a maximum value for the given collet configuration.

In further accordance with the purpose of the invention, a method is provided for optimizing collet design parameters for a type collet having a plurality of gripping jaws spaced around a common axis with resilient material between the gripping jaws, whereby a bar passing through the collet is securely held by the gripping jaws. The method comprises means for variably inputting design parameters of the collet of a given configuration. Means are also provided for calculating the radial force of the collet gripping jaws upon the bar, the radial force being dependent upon an axial force applied to the collet through a collet holder and collet nut. Means are further provided for calculating the torque developed on the bar from the radial forces of the gripping jaws just prior to toggle between the gripping jaws and the bar. The system includes means for calculating the moment generated due to toggle between the gripping jaws and bar at a predetermined toggle angle. Means are provided for varying the toggle angle in the moment calculating means until the moment generated reaches a maximum value. The method also calls for means for summing the maximum moment at toggle and torque developed just prior to toggle to give a total torque developed on the bar by the gripping jaws for the inputted design parameters of the collet. In this way, the total torque developed on the bar can be maximized by varying at least one design parameter through the design parameter inputting means so that an optimum set of design parameters can be determined.

In a preferred embodiment of the method according to the invention, a computer is provided with the radial force calculating means, torque calculating means, moment calculating means, toggle angle varying means, and summing means comprising respective software executed by the computer. Preferably, the computer includes a library of known design parameters for various known collet configurations for use by the software. The means for variably inputting design parameters is interfaceable with the computer so that at least one of the design parameters of the collet can be varied. Preferably, the computer further includes a library of known parameters for various collet nut geometries, with the radial force calculating means using the collet nut parameters to compute axial force imparted to the collet.

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

  • Fig. 1 is a perspective view of a collet according to the present invention, particularly a collet formed according to the process and method of the invention;
  • Fig. 2 is a partial component view of the collet depicted in Fig. 1, particularly illustrating the gripping jaws of the collet;
  • Fig. 3 is a front end view of the collet shown in Fig. 2;
  • Fig. 4 is a flow chart diagram depicting the sequence of steps and calculations according to the method and process of the invention;
  • Fig. 5 is a simplified schematic representation of the system according to the invention incorporating the process and method of Fig. 4;
  • Fig. 6 is a flow chart diagram depicting the steps and calculations according to the method for calculating torque at toggle condition;
  • Figs. 7a and 7b are diagrammatic depictions of collet thread geometries, particularly depicting the analysis parameters used in calculation of axial force;
  • Fig. 8a is a simplified component view of a gripping jaw cooperating with a collet holder to grip a bar, particularly illustrating the condition of toggle;
  • Fig. 8b is a diagram illustrating the contact width between a jaw and the bar;
  • Fig. 9 is a diagrammatic sketch particularly pointing out the analysis parameters used to calculate torque just prior to toggle;
  • Fig. 10 is another simplified diagrammatic sketch illustrating the concept of roll angle and maximum roll angle used in calculation of torque at toggle condition;
  • Fig. 11a is a detailed diagrammatic sketch illustrating the analysis variables used in the calculation of torque at toggle condition; and
  • Fig. 11b is a similar to Fig. 11a and shows the parameters used in elastic deformation toggle analysis.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the presently preferred embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings and figures. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features or steps illustrated or described as part of one embodiment of the method of the invention, can be used on another embodiment of the method to yield a still further embodiment of the method. Thus, it is intended that the present invention cover such modifications and variations as come within the scope of the appended claims and their equivalents. The numbering of components in the drawings is consistent throughout the application, with the same components having the same number in each of the drawings.

The method and apparatus according to the present invention relate to a collet of the type illustrated in Figs. 1 through 3. Collet 10 is actuated by engagement with the conical surface of a collet holder and collet nut (not shown). Those skilled in the art understand the operation of collet 10 with a collet holder and collet nut.

Collet 10 comprises resilient material 12 for holding a plurality of gripping jaws 16 in a desired spaced relation relative to each other. Preferably, resilient material 12 extends through perforations 28 within gripping jaws 16 so as to form essentially concentric rings of resilient material 12 through gripping jaws 16.

Collet 10 also comprises gripping means A for optimally holding a machine tool within collet 10. In a preferred embodiment, gripping means A comprises a plurality of gripping jaws 16 held by the resilient material 12 in a desired longitudinally and angularly spaced relation about longitudinal centerline axis 18 through collet 10. The gripping jaws have an exposed inner face 20 parallel to centerline axis 18, whereby the plurality of jaws 16 define an inner radius 22 of collet 10. The shaft or bar of a machine tool to be held by collet 10 is inserted through inner radius 22 of collet 10.

Gripping jaws 16 further include an angled exposed outer face 24 whereby the plurality of jaws 16 define a conical outer surface 26. Conical outer surface 26 matches the conical surface of the collet holder (not shown).

According to the method and process of the invention described in this section, applicant has determined that the gripping strength of the present collet is significantly increased compared to conventional collets by analyzing the torque generated by the collet on the machine tool or a test bar and optimizing the design parameters of gripping jaws 16 so as to generate maximum torque for a given collet configuration. Thus, gripping jaws 16 comprise at least one structural characteristic or dimension optimized to maximize the gripping strength of collet 10. The structural characteristics or dimension of jaws 16 may include, for example, the thickness of jaw 16, the number of jaws 16 within collet 10, or the type of material from which jaw 16 is formed. For example, a standard ER25 collet configuration has collet geometries based on DIN standards, such as inner radius, outer radius, angle of outer conical surface, etc. Once a particular collet configuration is selected, the industry standards and requirements are basically dictated by the appropriate engineering standards. However, applicants have determined that by optimizing certain design parameters of the collet gripping jaws, the gripping strength of a collet of that particular configuration can be maximized.

Applicant has also particularly determined that a degree of toggle between the gripping jaws and machine tool or bar is desirable in that it provides a maximum torque generated between the collet jaws and bar. Applicant has incorporated this desirable condition in his analysis in determining the optimum design parameters for the gripping jaws for maximizing total torque between the collet and tool held within.

The method and system for implementing the same according to the invention is represented generally in flow chart form in Figs. 4 to 6. The analysis steps indicated in the figures will be discussed in detail below. Table 1 provided below is a list of the variables and their meaning and default value used in the analysis steps.

It should be understood that the following description of the analysis steps according to the method and process of the present invention is but a preferred embodiment of the present method and not meant as a limitation thereof. The values calculated in the steps may be calculated or predicted in any manner of process, all of which fall within the scope and spirit of this invention. Additionally, the order of analysis steps presented is not limited to the order discussed but, can include any effective order.

Referring to Fig. 4, the various collet parameters and default values are entered at step 69, including collet holder and nut parameters, jaw design variables, material allowable stresses, coefficient of friction for collet nut, holder, and bar, test bar parameters, etc. At step 71 the maximum number of gripping jaws is determined for a given collet configuration and given jaw thickness. The maximum number of jaws is estimated using the inner radius of the collet, the jaw thickness, and the rubber coating thickness on each side of the jaw as follows:

Although not used particularly in the analysis, the angle of resilient material 12 between the jaws may be calculated assuming a uniform equal spacing between the jaws and a uniform resilient material coating thickness on each jaw face according to the following equation:

As discussed above, the collet 10 is engaged with a collet holder and collet nut (not shown in the figures). Engagement between the collet nut and collet holder imparts an axial force to the collet. As a result of this axial force, a radial force is developed between each jaw 16 and a test bar or machine tool shaft through the collet. The axial force or thrust developed due to tightening of the collet nut onto the collet holder is dependent upon the geometry of the threaded surfaces of the collet nut. The notation for this geometry is indicated in Figs. 7a and 7b. The thread geometry parameters may be obtained from engineering standards, such as the June, 1959 DIN 6341 standard (TR designation) or ISO 68 metric screw thread standard (M designation). The values for the collet nut thread geometry parameters obtained or calculated from the engineering standards are preferably stored in a library 68 for later retrieval and analysis.

At step 73, the parameters for a particular collet configuration are defined, preferably from stored in formation in a library 66 (Fig.3). The collet geometry parameters are based on DIN standards and are basically defined once a particularly collet configuration is selected. The analyst is prompted to select a particular collet design or configuration and the system or program then defines the various geometric data needed for the analysis. For example, table 2 is provided below as an example of collet geometry standards obtained from DIN 6499 for an 8° cone for an ER11, ER25, ER32, and ER40 collet designation.

The axial force calculation is executed at step 74. The total torque applied to the collet nut on the collet holder equals the sum of the torque necessary to develop an axial thrust on the collet and the torque necessary to overcome the collet thrust bearing friction. The applied torque to the collet nut is given by the equation:

If the term inside the parenthesis is defined as: 1 / (Ω) = 2π rm fn + L cos αn / (2π rm cosαn - fn L) then using the relationship for tan λ , the inverse relation is obtained: Ω = 1-fn / (cosαn)tanλ / (tanλ + fn / (cosαn)) As such, the expression for the applied torque to the nut may be written as: Tnut = W rm / (Ω) + W fcb Rc = W rm 1 / (Ω) + fcb Rc / (rm) then solved for the axial force on the entire collet W to obtain: W = Tnut / (rm1 / (Ω) + fcb Rc / (rm)) Now assuming that only the jaws carry any load and that each jaw is identical and located ideally so that each jaw is loaded in the same manner and in the same amount. That is, the axial force per jaw is: Wjaw = W / (Njaws)

It should be understood that the above calculations are but one means of predicting the axial force applied to the collet. The axial force may actually be predetermined and stored in an appropriate library for retrieval and analysis.

The radial force calculation is performed at step 75. As a result of the axial force which develops due to the tightening of the collet nut, a normal force develops between the collet holder surface and each gripping jaw. The total frictional force between the collet jaws and collet holder is the product of this normal force and the coefficient of friction between the jaws and collet holder. That is, Fjawfc = fc Fjawya Summing forces in the axial and radial directions gives the following two equations in two unknowns: ↑ Σ Faxial = fb Fjawradial - Wjaw + Fjawya sinαc + fc Fjawya cosαc = 0 → Σ Fradial = Fjawradial - Fjawya cosαc + fc Fjawya sinαc = 0 From these two equations, expressions for the normal force between the collet holder and each jaw, for the radial force transmitted between each jaw and the bar, and for the axial force are obtained and given by: Fjawya = Wjaw / ((fb + fc)cosαc + (1 - fbfc)sinαc) Fjawradial = Fjawya (cosαc-fcsinαc) Fjawaxial = Fjawya sinαc

In step 76, the torque due to Coulomb friction force per each gripping jaw is calculated for the condition of no slippage between the bar and gripping jaws. Slippage is essentially the condition where the gripping jaws have "rocked" to such a degree that they are basically no longer applying force to the test bar which therefore is essentially free to rotate within the collet. The radial force transmitted between the jaws and the test bar has associated frictional forces that develop at the inner face between each jaw and the bar. The torque due to the Coulomb friction force per jaw is calculated as follows: TjawCF = Fjawf Rb = fb Fjawradial Rb The total torque developed without slippage is this value times the number of jaws in the collet, according to the following: TtotalCF = Njaws TjawCF = Njaws Fjawf Rb = Njaws fb Fjawradial Rb The torque results from the frictional forces acting between the bar and each jaw edge. The frictional force is calculated based on Coulomb's Law of Friction which is independent of contact area. As such, in this part of the analysis, the thickness of the jaw and the engagement length along the inner face between the bar and jaw edges do not effect the torque resulting from Coulomb friction forces.

At step 77, it is predicted whether slip will occur between the test bar and the jaws based on the geometry of the jaws. Slip will occur when: tanα1 > fb where α1 = tan-1t / (h1) = tan-1t / (Rc1 - Rb - δclear) It is desired to inform the analyst whether the parameters for the jaw blade he has selected will result in slipping between the jaw blades and test bar.

As illustrated in Fig. 8a, at some degree of slipping between the jaws and bar, the jaw will "toggle" or "rock" and lose contact with the bar and collet holder at certain points along the length of the jaw. At toggle condition, the contacting surface area will be reduced. A degree of toggling between the jaws and bar may be desired in that torque developed between the jaws and bar is actually increased.

To account for differences due to geometric parameters of the jaws, such as jaw thickness, in the torque calculation, the conditions "just prior" to toggle are examined according to an elastic contact analysis (Hertzian Contact Analysis). Basically, the test bar is treated as a long cylinder in contact with a flat semi-infinite plane subjected to a line of force P as shown in Fig. 8b. The contact region between the cylinder and plane is equal to twice the semi-contact width (2a) for the entire cylinder length. The semi-contact width (a) is calculated according to the following: α = sqrt(4PRb / (πE*))    where E* = 1-ν2bar / (Ebar) + 1-ν2jaw / (Ejaw)-1 P = Fjawradial / (Lbar) This approach is valid as long as the jaw thickness is much larger than twice the semi-contact width.

In step 78 according to the present method, torque is calculated at a condition just prior to toggle between the jaws and bar. As illustrated in Fig. 9, just prior to toggle occurring, the line of action of the radial force shifts to the outer corner of each jaw. Since the depth of the jaw varies along the engagement length thereof, the distance or height of the segment must be calculated. The engagement length between the jaw and the collet holder is projected onto the bar and then this length is divided into a number of segments (Nseg) which may be set at default value such as 20. Then, by summing forces in the radial and tangential directions and summing moments about the center of the bar, the torque just prior to toggle for each segment is obtained. Summing these values for each segment gives the total torque just prior to toggle for each jaw. This approach gives the following equations: TjawJPT = sum(i=1NsegFjawradialiRbfb + cosαijaw(sinαijaw - 1)) = TjawCF + sum(i=1NsegFjawradialiRbcosαijaw(sinαijaw -1)) The total torque developed just prior to toggle is this value times the number of jaws in the collet, according to the following: TtotalJPT = Njaws TjawJPT

Method 70 further includes step 79 for calculating torque at toggle condition between the jaws and bar. The torque calculation at toggle condition analysis is charted in detail in Fig. 6. Since the toggle may not extend along the full length of each jaw, the jaw is divided at step 100 into a number of segments Nseg along the length thereof. The calculations proceed as a double loop. For each increment in bar rotation, or "toggle angle," the elastic deformation for each segment of a jaw is computed as well as its radial frictional force.

At step 101, the toggle angle for each jaw is determined. As shown in Fig. 10, the toggle angle is calculated based on the semi-contact width obtained from the Hertz contact analysis. The toggle angle is the angle through which a jaw can rotate within the distance defined by the semi-contact width. The toggle angle is calculated as follows:

It is assumed that the initial toggle angle and subsequent increment of toggle angle are equal, in other words, the toggle angle will be incremented each pass by its initial value. It should be understood that there is a limit for the toggle angle above which no torque will be generated.

The torque at toggle condition analysis and calculations will be discussed in detail below but, basically, the torque at toggle accounts for the torque generated due to elastic deformation of the jaws and torque due to elastic radial (Coulomb friction) force once the jaw edge has "yielded." Thus, the analysis considers plastic deformation of the jaws as well. It should be understood that the type of material from which the jaws are formed will thus effect the torque at toggle analysis since yielding or plastic deformation is a factor of the allowable stress for the type material. Material composition of the jaws is thus a design parameter of the jaws which can be varied to optimize the gripping strength of the collet.

The following analysis of the torque calculation at toggle condition is represented sequentially in flow-chart form in Fig. 6. Once the jaw has been segmented at step 100 and the toggle angle calculated at step 101 as above, the analysis is executed for each segment. Although the calculations will be explained in detail below, the basic steps are as follows. At step 103, the segment Ni is checked for previous yielding and slip. If such occurred, this segment is ignored at 104 and the next segment analyzed, and so forth. If yielding and slip did not occur, the torque for the segment due to elastic deformation is calculated at 105. This torque is summed for all segments at 106. At step 107, the segment is checked for initial yielding. If such has not occurred, then no more torque is being generated and, at 108, the analysis skips to the next segment. If yielding has occurred, the jaw shortening is recalculated at step 109 to account for plastic deformation. Then, at step 110, slip is checked at the plastic deformation condition. If slip occurs, no torque is generated and the analysis skips to the next segment at step 111. If slip does not occur, the torque generated due to elastic radial force (Coulomb force) at the yielded condition is calculated at step 112. This torque is summed for all the segments at step 113. The next segment is analyzed at step 117.

At step 114, the total torque at toggle condition is calculated for all jaws from the sums of step 113 and 106. If this total torque is not a maximum valve at 115, then at 116 the toggle angle is incremented at the analysis repeated for that segment. The total torque at toggle condition is not a maximum if it is less than the previous value, the previous value therefore being the maximum value.

The calculations and instructions for executing the steps just described are as follows:

  • Initialize variables IPASS=0 , IYLDi=0 for all segments
  • Increment the bar rotation angle &thetas;=&thetas;+Δ&thetas; where initial value of &thetas; = αbarscw. and Δ&thetas; = αbarscw, and set IPASS=IPASS+1
  • Calculate the length of each segment along the jaw length assuming uniform spacing b=l/Nseg where l is the engagement length of the collet and collet holder.
  • Calculate Δt = 1 / (2)t - α - Rb&thetas;
  • For each segment i = 1, Nseg , first check to see if IYLDi is less than zero. If it is, then this jaw segment is not in contact with the bar and so go to the next segment. If it is greater than or equal to zero then proceed. Set the iteration counter for segment yielding to zero (m=0) and do the following calculations:

    Average outer radius of collet for the ith segment (Rc)i = Rc1 - (2i) - 1 / (2Nseg) (Rc1 - Rα)

    Width of jaw at the ith segment hi = (Rc)i - Rb - δclear where   δclear = Rinnerc - Rb

    Calculate the roll angle for the ith segment &thetas;iroll = αi+scw = tan-11 / (2)t+α / (hi) - tan-11 / (2)t / (hi)

    Calculate the maximum rotation angle for the ith segment &thetas;imax = tan-11 / (2)t / (hi+Rb)

    If &thetas; ≥ &thetas;imax then go to the next segment.

    Angle between line AC and right edge of jaw (before toggle) for ith segment 2)i = tan-1t / (hi)

    Length of the line AC for the ith segment before toggle zi = hi / (cos(α2)i)

    Angle between Line A'C and right edge of jaw (after toggle) for ith segment 2n)i = (α2)i + &thetas;

    Length of the line A'C for the ith segment after toggle (zn)i = hi / (cos(α2n)i)

    Shortening of this diagonal line for the ith segment averaged over each jaw is n)i = zi - (zn)i

    If (δn)i < 0 then go to the next segment.

    From strength of materials, the deformation of an axially loaded member is (PL)/(EA). Thus the force related to this shortening and acting along the line A'C is (Fzn)i = (δn)i Ejaw A0i / ((zn)i) where A0i = 2ab

    Total radial force at the jaw corner for the ith segment (Fradial)0i = Fjawradiali + (Fzn)i cos(α2n)i

    Bearing stress for the ith segment bearn)0i = (Fradial)i / (Ai0)

    Check for yielding of the ith segment. If bearn)0i < σbearall

    Then calculate the moment arm from the center of the bar to the force xi = (Rb + hitan(α2n)i - 1 / (2)t + α tan(α2n)i)sin (α2n)i

    Calculate the moment for the ith segment (Mx)i = xi (Fzn)'i

    Accumulate the moments for all segments along the jaw MT = MT + (Mx)i

    Go to next segment

    If it is greater than or equal to the allowable bearing stress then decrease the deformations and re-calculate the force and bearing stress.

    Set yield flag IYLDi=IPASS where IPASS is the pass number for incrementing the toggle angle

    If the new deformation is less than zero, then set it to the deformation of the previous estimate

    Calculate the new force related to the new shortening (Fzn)mi = (δn)mi Ejaw Ami / ((zn)i) where Ami = bΔt / (cos&thetas;)

    Calculate new total radial force at the jaw corner for the ith segment (Fradial)mi = Fjawradiali + (Fzn)mi cos(α2n)i

    Calculate new bearing stress bearn)mi = (Fradial)mi / (Aim)

    Check for yielding of the ith segment. If bearn)mi > σbearall then adjust the iteration counter to m=m+1 and loop back to re-calculate the deformations1 the radial force, and bearing stress. Maximum of 100 iterations is set.

    If this new bearing stress is less than the allowable value for the bearing stress, then the amount of yielding is determined.

    If this is the initial yielding (zep)i = 0 then calculate the maximum length of line A'C. At this condition the points O, A', and C are colinear and the line A'C has a maximum length of (zn)'i = (zn)i - (δn)i + (δn)mi

    Now assign (zep)i = (zn)'i

    Otherwise use the previously calculated value.

    Calculate the elastic shortening of line A'C d' = (zep)i - 1 / (2) t / (sin&thetas;) - Rb = (zep)i - lCD where lCD is the length required for contact.

    If d' is greater than zero then calculate the corresponding elastic force due to this elastic shortening. (Fzn)i = d' Ejaw A' / ((zep)i) where A' = 2ab

    Now calculate the moment due to the Coulomb friction force for the ith segment (Mx)i = Rbfb (Fzn)i

    Accumulate the moments MT = MT + (Mx)i

    Go to next segment.

    If d' is less than or equal to zero then this segment has lost contact with the bar. Set the yield flag to a negative value IYLDi = -IYLDi

    Go to next segment.

    Calculate the total moment due to "toggle" for all jaws in the collet MtotalT = Njaws MT

    Calculate the total torque TtotalT = TtotalJPT + MtotalT

    Increment &thetas; and repeat "toggle" calculations until MtotalT is a maximum.

For each increment of toggle angle, the total moment due to toggle is calculated for all jaws in the collet. If this total moment is not a maximum value, then the toggle angle is incremented and the toggle calculations re-executed until the maximum torque at toggle is determined. The total torque on the bar is the sum of the torque just prior to toggle and the total moment at toggle.

The gripping strength of the collet is directly related to the total torque generated on the bar or tool extending through the collet. Thus, it should be understood that by varying the design parameters of the collet jaws and calculating total torque for each parameter change, an optimum set of parameters can be determined for maximizing collet gripping strength. For example, the graph provided below illustrates the effect on total torque, and thus gripping strength, of varying the jaw thickness for an ER25-8 collet configuration in increments of 0.01 inches. It was assumed that the default values of table 1 are acceptable and that the applied torque to nut on the collet holder was 350 in.-lbs. It was also assumed that, at most, only 10 jaws should be used in the design and that both extremes in bar or tool shaft diameter should be considered. As the graph illustrates, as jaw thickness increases, there is an increase in total torque (including toggle) up to a thickness of approximately 0.10 inches. Above this thickness, the total torque decreases. The effect of bar diameter on the total torque for a given jaw thickness is also indicated. Thus it should be readily understood how the analysis method and system according to the present invention can optimize jaw thickness to maximize gripping strength of the collet.

The graph provided below illustrates the effect of varying the number of jaws for an ER25-8 collet configuration assuming a jaw thickness of 0.07 inches. As the graph shows, generally as the number of jaws increases, there is an increase in total torque. However, between 10 and 14 jaws the total torque increased only 9%. Also, the graph illustrates to 15 jaws, and depending on the degree of resilient material on the jaw faces, the maximum number of jaws may decrease.

The above graphs illustrate the effect of varying only one parameter while assuming default or constant values for the other jaw parameters. The analysis method may also be executed to determine the optimum combination of parameters, such as thickness, number, and type material, for the jaws of a given configuration.

The analysis method of the present invention is preferably configured in a system 50, generally depicted in Figs 4 and 5. Means 52 are provided for varying the jaw parameters so as to optimize particular parameters. Means 54 are provided for calculating the radial force of the collet jaws upon the bar, as explained above. Means 56 are for calculating torque developed on the bar just prior to toggle between the jaw and bar, also as explained above. Means 58 are provided for calculating the maximum moment at toggle condition and for calculating the total torque developed on the bar 60. In a preferred embodiment, the various means comprise applicable software 64 for executing the calculations with system 50 being a computer, generally 62. System 50 preferably comprises a library 66 of parameters known for the wide variety of conventional collet configurations, and library 68 for collet nut geometry parameters. Interface means, generally 52, are provided for allowing an analyst to generate DIN ASME standard data, define default values, input collet parameters, etc.

As described above, the present invention includes method of design of a machine tool collet having gripping means for optimally holding a machine tool. The gripping means include jaws having at least one parameter optimized for maximizing the gripping strength of the collet. For example, collet 10 may have the number of jaws 16, or thickness of jaws 16, or material composition of jaws 16 optimized.

Table 3 below is a list of preferred embodiments of the present inventive collet designed according to the present analysis. For different collet configurations (i.e., TG50 and ER25) and capacity ranges, a preferred optimum number and thickness of jaw blades has been determined. The jaw blades are formed of 1070 high carbon steel. For ease of manufacture, the varying thicknesses of the jaw blades was limited to commercially available thicknesses. For example, 1070 high carbon steel is commercially available in thicknesses of 0.055, 0.075, and 0.100 inches, among others. Thus, for each of the configurations and capacities, the commercially available thicknesses of 1070 steel were analyzed to determine which thickness was optimum. Likewise, for each of the different thicknesses, the optimum number of jaw blades was determined until an optimum combination of blade number and blade thickness was determined.

It is desired in the industry to provide a collet which is effective over as wide a range as possible so as to limit the number of collets required. The present inventive method aids in this goal in that it allows for defining a collet which provides a high gripping strength over a wider range even though the combination of parameters may not be the best for a specific individual capacity within the range of the collet. For example, a preferred TG75 collet designed according to the invention with a capacity range of 17/32 to 9/16 inches comprises 8 jaw blades having a thickness of 0.130 inches. The combination of 8 blades and thickness of 0.130 inches is optimum in that it provides the highest overall gripping strength for a single collet within the given range even though for a collet having a capacity of only 9/16 inches, 7 jaw blades having a thickness of 0.130 inches produces a slightly greater total torque with toggle. However, the gripping strength provided by the collet having 8 blades at a capacity of 9/16 inches is only slightly less and is more than adequate for use in the industry. Thus, the parameters of number of blades and thickness of blades has been optimized over the range of 17/32 to 9/16 inches.

In this manner, the present method of design of machine tool collets according to the invention offers a significant advantage over the state of the art. For example, with conventional split steel collets of the TG75 configuration, 17 collets are necessary to cover the range of 5/32 to 5/8 inches, whereas only 8 Rubber-Flex collets designed according to the method of the present invention would be needed. Thus, the present inventive method for optimizing the gripping strength of a Rubber-Flex collet allows for precisely defining collets which are adequate over a wider range thereby significantly reducing the number of collets necessary arid manufacturing costs. Table 3 below includes the combinations which have been optimized to provide a greater overall torque at toggle condition for the collet over the stated ranges.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope of the claims. Thus, it is intended that the present invention cover such modifications and variations as come within the scope of the appended claims.


Anspruch[de]
  1. Verfahren zum Gestalten einer Spannpatrone (10) eines Maschinenwerkzeugs, welche dadurch betätigt wird, daß sich diese in Eingriff mit einer Eingriffsfläche einer Spannpatronenhalterung befindet, wobei
    • die Spannpatrone (10) eine gegebene Außendurchmesseranordnung und Innendurchmesseraufnahmefähigkeit aufweist, wobei
    • eine Vielzahl von Greifbacken (16) in einer erwünschten Beziehung in Längen- und Winkelabstand um eine Längs-Mittellinienachse (18) herum durch die Spannpatrone (10) gehalten wird, wobei
    • die Greifbacken (16) eine Innenfläche (20) aufweisen, welche zu der Mittellinienachse (18) parallel ist, wodurch die Vielzahl von Greifbacken (16) eine Öffnung durch die Spannpatrone (10) hindurch zum Aufnehmen eines Werkzeugschafts definiert, wobei die Öffnung die Aufnahmefähigkeit der Spannpatrone (10) definiert, wobei
    • die Greifbacken (16) eine Außenfläche (24) aufweisen, wodurch die Vielzahl von Greifbacken (16) eine Außenoberfläche (26) für den Eingriff der Spannpatronenhalterungs-Aufnahmefläche definieren, wobei die Außenfläche (24) eine Außendurchmesseranordnung der Spannpatrone (10) definiert, wobei
    • die Anzahl der Greifbacken (16) einen ersten veränderlichen Gestaltungsparameter der Spannpatrone (10) definiert, wobei
    • die Dicke der Greifbacken (16) einen zweiten veränderlichen Gestaltungsparameter der Spannpatrone (10) definiert;
    • wobei ein elastisches Material (12) zwischen den Greifbacken (16) zum Halten der Vielzahl von Greifbacken (16) in der erwünschten Beziehung in Abstand angeordnet ist,

      dadurch gekennzeichnet, daß
    • das Typenmaterial der Greifbacken (16) einen dritten veränderlichen Gestaltungsparameter der Spannpatrone (10) definiert;
    • wobei ferner für eine gegebene Anordnung und Aufnahmefähigkeit der Spannpatrone (10) mindestens einer der veränderlichen Gestaltungsparameter für gegebene Werte der anderen veränderlichen Gestaltungsparameter ausgewählt wird, wobei
    • mindestens einer der anderen Gestaltungsparameter geändert wird, bis ein maximales Gesamtdrehmoment (Mttotal) zusammen mit den gegebenen Werten des anderen veränderlichen Parameters (bzw. der Parameter) (Tabelle 3) erreicht wird, so daß die Spannpatrone (10) bezüglich des mindestens einen Gestaltungsparameters das maximal mögliche Gesamtdrehmoment (Mttotal) an einer dadurch hindurch verlaufenden Stange erzeugt, wobei das maximale Gesamtdrehmoment (Mttotal) aus dem Drehmoment an der Stange, welches durch die Greifbacken (16) unmittelbar vor einem Biegezustand erzeugt wird, welcher zwischen den Greifbacken (16) und der Stange besteht, und einer Gesamt-Drehmomentkraft durch die Greifbacken (16), welche bei einem Biegezustand erzeugt wird, besteht.
  2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß die Parameter einer Anzahl von Greifbacken (16) und einer Dicke von Greifbacken (16) zusammen mit einem gegebenen Material von Greifbacken (16) bezüglich des maximalen Gesamtdrehmoments (MTtotal) optimiert wurden, um einen breiten Aufnahmefähigkeitsbereich zu erhalten, wobei das Gesamtdrehmoment annehmbar ist.
  3. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß für einen gegebenen Typ eines elastischen Materials und einen gegebenen Typ eines Backenmaterials die Anzahl und die Dicke der Backen (16) bestimmt werden durch:
    • Bestimmen der Radialkraft der Greifbacken (16) auf eine Stange, welche durch die Spannpatrone (10) hindurch verlaufend angeordnet ist, wobei die Radialkraft von einer auf die Spannpatrone (10) ausgeübten Axialkraft abhängt;
    • Bestimmen des Drehmoments an der Stange, welches aus den Radialkräften der Greifbacken (16) unmittelbar vor einem Biegezustand zwischen den Greifbacken (16) und der Stange entwickelt wird;
    • Bestimmen der Gesamt-Drehmomentkraft, welche zwischen den Greifbacken (16) und der durch die Spannpatrone (10) verlaufenden Stange bei einem Biegezustand für einen gegebenen Biegewinkel erzeugt wird;
    • Ändern des Biegewinkels, bis die Gesamt-Drehmomentkraft zwischen den Greifbacken (16) und der Stange bei einem Biegezustand einen Maximalwert erreicht; und
    • Bestimmen des Gesamtdrehmoments an der Stange durch Summieren des Drehmoments vor einem Biegen und der maximalen Gesamt-Drehmomentkraft bei einer Biegebedingung;
    • wodurch eine optimale Anzahl und Dicke der Greifbacken (16) für eine gegebene Anordnung und Aufnahmefähigkeit einer Spannpatrone (10) dadurch bestimmt werden, daß die Anzahl und die Dicke der Greifbacken (16) geändert werden, bis das Gesamtdrehmoment für eine Anzahl oder eine Dicke der Greifbacken (16) maximiert ist.
  4. Verfahren nach einem oder mehreren der Ansprüche 1 bis 3, dadurch gekennzeichnet, daß die Dicke der Greifbacken (16) dadurch bestimmt wird, daß eine Dicke der Greifbacken (16) für eine gegebene Anordnung und Aufnahmefähigkeit einer Spannpatrone (10) und eine gegebene Anzahl der Greifbacken (16) geändert wird, bis eine Dicke bestimmt ist, welche ein maximales Gesamtdrehmoment (Mttotal) für die Spannpatrone (10) erzeugt.
  5. Verfahren nach einem oder mehreren der Ansprüche 1 bis 4, dadurch gekennzeichnet, daß die Anzahl der Greifbacken (16) dadurch bestimmt wird, daß die Anzahl der Greifbacken (16) für eine gegebene Anordnung und Aufnahmefähigkeit einer Spannpatrone (10) und eine gegebene Dicke der Greifbacken (16) geändert wird, bis eine Anzahl bestimmt ist, welche ein maximales Gesamtdrehmoment (Mttotal) für die Spannpatrone (10) erzeugt.
  6. Verfahren nach einem oder mehreren der Ansprüche 1 bis 5, dadurch gekennzeichnet, daß das Typenmaterial der Greifbacken (16) dadurch bestimmt wird, daß das Typenmaterial für eine gegebene Anordnung und Aufnahmefähigkeit einer Spannpatrone und eine gegebene Anzahl und Dicke der Greifbacken (16) geändert wird, bis ein Typenmaterial bestimmt ist, welches ein maximales Gesamtdrehmoment (Mttotal) für die Spannpatrone (10) erzeugt.
  7. Verfahren nach einem oder mehreren der Ansprüche 1 bis 6, dadurch gekennzeichnet, daß die Dicke, die Anzahl und das Typenmaterial der Greifbacken (16) dadurch bestimmt werden, daß Dicke, Anzahl und Typenmaterial geändert werden, bis eine Verbindung von Dicke, Anzahl und Typenmaterial bestimmt ist, welche ein maximales Gesamtdrehmoment für die Spannpatrone (10) erzeugt.
Anspruch[en]
  1. A method to design a machine tool collet (10) which is actuated by engagement with a mating surface of a collet holder,
    • said collet (10) being of a given outer diameter configuration and inner diameter capacity,
    • a plurality of gripping jaws (16) held in a desired longitudinally and angularly spaced relation about a longitudinal centerline axis (18) through said collet(10),
    • said gripping jaws (16) having an inner face (20) parallel to the centerline axis (18) whereby said plurality of gripping jaws (16) define an opening through said collet (10) for receiving a tool shank, said opening defining the capacity of said collet(10),
    • said gripping jaws (16) having an outer face (24) whereby said plurality of gripping jaws (16) defines an outer surface (26) for engaging the collet holder mating surface,
    • said outer face (24) defining an outer diameter configuration of said collet (10),
    • the number of said gripping jaws (16) defining a first variable design parameter of said collet (10),
    • the thickness of said gripping jaws (16) defining a second variable design parameter of said collet (10);
    • resilient material (12) disposed between said gripping jaws (16) for holding said plurality of gripping jaws (16) in said desired spaced relation,

      characterised in that
    • the type material of said gripping jaws (16) defining a third variable design parameter of said collet (10);
    • and wherein for a given configuration and capacity of said collet (10), at least one of said variable design parameters being selected for given values of said other variable design parameters,
    • at least one of the other parameters being varied until maximum total torque (Mttotal) is reached together with the given values of said other variable design parameter(s) (table 3), so that with respect to said at least one design parameter said collet (10) generates the maximum total torque (MTtotal) possible on a bar passing therethrough,
    • maximum total torque (Mttotal) being the torque generated by said gripping jaws (16) on said bar just prior to a toggle condition existing between said gripping jaws (16) and said bar, and total moment force generated by said gripping jaws (16) at a toggle condition.
  2. Method according to claim 1, characterised in that the parameters of number of gripping jaws (16) and thickness of gripping jaws (16) together with a given material of gripping jaws (16) were optimized in respect of the maximum total torque (MTtotal)to get a wide range of jaw capacity, where the total torque is acceptible.
  3. Method according to claim 1 or 2, characterised in that for a given type of resilient material and given type of jaw material the number and thickness of said jaws (16) being determined by:
    • determining the radial force of said gripping jaws (16) upon a bar disposed through said collet (10), the radial force being dependent upon an axial force applied to said collet (10);
    • determining the torque developed on the bar from the radial forces of said gripping jaws (16) just prior to a toggle condition between said gripping jaws (16) and the bar;
    • determining the total moment force generated between said gripping jaws (16) and the bar through said collet (10) at toggle condition for a given toggle angle;
    • varying the toggle angle until the total moment force between said gripping jaws (16) and the bar at toggle condition reaches a maximum; and
    • determining the total torque on the bar by summing the torque prior to toggle and the maximum total moment force at toggle condition;
    • whereby an optimum number and thickness of said gripping jaws (16) for a given collet (10) configuration and capacity is determined by varying the number and thickness of said gripping jaws (16) until the total torque is maximized for number or thickness of said gripping jaws (16).
  4. Method according to one or more of claims 1 to 3, characterised in that the thickness of said gripping jaws (16) is determined by varying thickness of said gripping jaws (16) for a given collet (10) configuration and capacity and given number of said gripping jaws (16) until a thickness generating maximum total torque (Mttotal) for said collet (10) is determined.
  5. Method according to one or more of claims 1 to 4, characterised in that the number of said gripping jaws (16) is determined by varying the number of said gripping jaws (16) for a given collet configuration and capacity and given thickness of said gripping jaws (16) until a number generating maximum total torque (Mttotal) for said collet(10) is determined.
  6. Method according to one or more of claims 1 to 5, characterised in that the type material of said gripping jaws (16) is determined by varying the type material for a given collet configuration and capacity and given number and thickness of said gripping jaws (16) until a type material generating maximum total torque (Mttotal) for said collet (10) is determined.
  7. Method according to one or more of claims 1 to 6, characterised in that the thickness, number, and type material of said gripping jaws (16) is determined by varying the combination of thickness, number, and type material until a combination of thickness, number, and type material generating maximum total torque (Mttotal) for said collet (10) is determined.
Anspruch[fr]
  1. Procédé pour concevoir une pince de serrage (10) de machine outil qui est actionnée par coopération avec une surface s'adaptant d'un support de pince de serrage,
    • la pince de serrage (10) étant d'une configuration de diamètre extérieur donnée et d'une capacité de diamètre intérieur donnée,
    • une pluralité de mâchoires (16) de serrage étant maintenues à distance souhaitée longitudinalement et angulairement les unes des autres par rapport à un axe (18) longitudinal de ligne centrale passant par la pince de serrage (10),
    • les mâchoires (16) de serrage ayant une face (20) intérieure parallèle à l'axe (18) de ligne centrale, la pluralité de mâchoires (16) de serrage définissant une ouverture dans la pince de serrage (10) pour recevoir une tige d'outil, l'ouverture définissant la capacité de la pince de serrage (10),
    • les mâchoires (16) de serrage ayant une face (24) extérieure, la pluralité de mâchoires (16) de serrage définissant ainsi une surface (26) extérieure pour coopérer avec la surface s'adaptant du support de pince de serrage, la face (24) extérieure définissant une configuration à diamètre extérieur de la pince de serrage (10),
    • le nombre de mâchoires (16) de serrage définissant un premier paramètre de conception variable de la pince de serrage (10),
    • l'épaisseur des mâchoires (16) de serrage définissant un second paramètre de conception variable de la pince de serrage (10),
    • du matériau (12) élastique étant disposé entre les mâchoires (16) de serrage pour maintenir la pluralité de mâchoires (16) de serrage à distance souhaitée les unes des autres,

      caractérisé en ce que le type de matériau des mâchoires (16) de serrage définit un troisième paramètre de conception variable de la pince de serrage (10) ; et pour une configuration donnée et une capacité donnée de la pince de serrage (10), au moins l'un des paramètres de conception variables est sélectionné pour des valeurs données des autres paramètres de conception variables,
    • au moins l'un des autres paramètres est modifié jusqu'à ce que le couple maximum total (Mttotal) soit atteint ainsi que les valeurs données de l'autre ou des autres paramètre(s) de conception variable(s) de sorte que en ce qui concerne ledit au moins un paramètre de conception, la pince de serrage (10) produit le couple (MTtotal) maximum total possible sur une barre passant à travers elle, le couple (Mttotal) maximum étant le couple produit par les mâchoires (16) de serrage sur la barre juste avant un état de garrot existant entre les mâchoires (16) de serrage et la barre, et la force de moment total produite par les mâchoires (16) de serrage à un état de garrot.
  2. Procédé suivant la revendication 1, caractérisé en ce que les paramètres que sont le nombre de mâchoires (16) de serrage et l'épaisseur de mâchoires (16) de serrage, en même temps qu'un matériau donné pour les mâchoires (16) de serrage, sont optimisés en ce qui concerne le couple (MTtotal) maximum pour obtenir un grand domaine de capacité de mâchoires, dans lequel le couple total est acceptable.
  3. Procédé suivant la revendication 1 ou 2, caractérisé en ce que pour un type donné de matériau élastique et un type donné de matériau de mâchoires, le nombre et l'épaisseur des mâchoires (16) sont déterminés par :
    • la détermination de la force radiale des mâchoires (16) de serrage sur une barre disposée à travers la pince (10) de serrage, la force radiale étant fonction d'une force axiale appliquée à la pince de serrage (10) ;
    • la détermination du couple développé sur la barre à partir des forces radiales des mâchoires (16) de serrage juste avant un état de garrot entre les mâchoires (16) de serrage et la barre ;
    • la détermination de la force de moment total produite entre les mâchoires (16) de serrage et la barre passant dans la pince de serrage (10) à l'état de garrot pour un angle de garrot donné ;
    • la modification de l'angle de garrot jusqu'à ce que la force de moment total entre les mâchoires (16) de serrage et la barre à l'état de garrot atteigne un maximum ; et
    • la détermination du couple total sur la barre en additionnant le couple avant le garrot et la force de moment total maximum à l'état de garrot ;
    • grâce à quoi un nombre et une épaisseur optimisés des mâchoires (16) de serrage pour une capacité et une configuration données de pince de serrage (10) sont déterminés en modifiant le nombre et l'épaisseur des mâchoires (16) de serrage jusqu'à ce que le couple total soit rendu maximum pour le nombre ou l'épaisseur des mâchoires (16) de serrage.
  4. Procédé suivant l'une ou plusieurs des revendications 1 à 3, caractérisé en ce que l'épaisseur des mâchoires (16) de serrage est déterminée en modifiant l'épaisseur des mâchoires (16) de serrage pour une capacité et une configuration données d'une pince de serrage (10) et pour un nombre donné des mâchoires (16) de serrage jusqu'à ce qu'une épaisseur produisant le couple (Mttotal) total maximum pour la pince du serrage (10) soit déterminée.
  5. Procédé suivant l'une ou plusieurs des revendications 1 à 4, caractérisé en ce que le nombre des mâchoires (16) de serrage est déterminé en modifiant le nombre des mâchoires (16) de serrage pour une capacité et une configuration données de pince de serrage et une épaisseur donnée des mâchoires (16) de serrage jusqu'à ce que l'on détermine un nombre produisant le couple (Mttotal) total maximum pour la pince de serrage (10).
  6. Procédé suivant l'une ou plusieurs des revendications 1 à 5, caractérisé en ce que le type de matériau des mâchoires (16) de serrage est déterminé en faisant varier le type de matériau pour une configuration et une capacité données de pince de serrage et une épaisseur et un nombre donnés des mâchoires (16) de serrage, jusqu'à ce que l'on détermine un type de matériau produisant le couple (MTtotal) total maximum pour la pince de serrage (10).
  7. Procédé suivant l'une ou plusieurs des revendications 1 à 6, caractérisé en ce que l'épaisseur, le nombre et le type de matériau des mâchoires (16) de serrage sont déterminés en modifiant la combinaison de l'épaisseur, du nombre et du type de matériau jusqu'à ce que l'on détermine une combinaison d'épaisseur, de nombre et de type de matériau produisant le couple (Mttotal) total maximum pour la pince de serrage (10).






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