There is a class of powered mobile machines, such as floor scrubbers
and sweepers, in which the machine is operated by an attendant walking behind it.
Machines of this type are used to clean large floor areas such as factories, and
for such indoor service a battery powered machine is usually preferred. In the
case of a scrubber, the large areas to be scrubbed necessitate sizeable water
tanks on the machine which, along with the heavy batteries, cause the machine to
be so heavy that a powered traction drive is essential and power assisted steering
is desirable. Some walk-behind scrubbers use one traction motor driving two drive
wheels through a differential gear. On such scrubbers individual clutches or brakes
on the drive wheels have been used to assist steering, but some of these have been
less durable than desired. Other scrubbers have been fitted with two traction
motors, one to power each drive wheel, with means being provided for the operator
to control the speeds of these motors in unison for speed control and differentially
for power steering. This is an improvement over the single motor approach, and
is coming to be the common method, at least in the heavier machines. However, the
control means which have been used still do not provide optimum ease of handling.
They tend to respond slower than smaller scrubbers which are light enough to be
steered manually. A faster steering response can be obtained if the operator can
help steer the machine by manually pushing on the controls to supplement the power
steering, but pushing on the controls of some models may increase the machine travel
speed to maximum before any manual steering occurs, which could be hazardous.
Some machines provide a programmed rate of change in the differential speed of
the two motors, which turns the machine at a pre-established rate even though the
operator might want to make a quicker turn under some circumstances.
Therefore in this class of machines there is a need for a control
system that will make a machine more responsive and maneuverable than previously
available models. It should provide full power steering while at the same time
permitting the operator to apply manual force to the machine to assist the steering
without affecting the speed control or power steering. It should cause steering
and travel speed to respond in proportion to the degree of movement given to the
controls rather than at a preprogrammed rate. Also, it should be capable of making
a turn as sharp as turning about the centerline of the machine, and without forward
or reverse travel if desired, for maximum maneuverability in tight spaces. The
present invention provides these improvements.
Summary of the Invention
A machine, which may be a floor maintenance machine such as a sweeper,
scrubber or the like, is operated by an attendant walking behind it. A floor scrubber
will be used for illustration. The scrubber has two drive wheels that support a
substantial portion of its weight. Each drive wheel is powered by an individual
electric motor which is capable of forward or reverse rotation.
In the preferred embodiment of the invention each of these motors
is controlled by a commercially available solid state electronic motor controller,
and each of these in turn is controlled by a potentiometer. The potentiometers
are made to signal neutral or no motor rotation to the controllers at an intermediate
voltage. Moving the potentiometers from this intermediate voltage to a higher voltage
produces one direction of motor rotation, while moving them from the intermediate
voltage to a lower voltage produces the opposite direction of motor rotation.
Thus external switches are not needed for reversing the motors.
The two potentiometers are mechanically linked to a straight transverse
handlebar which is located at the rear of the machine where it is convenient to
the operator. The handlebar is attached to the frame of the machine by a central
pivot bracket in such a way that the handlebar may be rotated or twisted about
its own long centerline, and also tilted or pivoted about a central axis. This
axis is chosen for the comfort of the operator, and seems best when the ends of
the handlebar tilt down and forward or up and back at about 30 degrees from vertical
because this is substantially in line with the arms of an average height operator.
The linkages which connect the potentiometers to the handlebar cause
both potentiometers to move equally and in the same direction when the handlebar
is rotated about its long centerline, but equally and in opposite directions when
the handlebar is tilted. Since the two potentiometers control the two drive motors,
this arrangement results in a control system whereby the operator rotates the handlebar
forward to go forward, and the farther he or she rotates it the faster the travel
speed becomes. The operator rotates the handlebar backward for reverse travel,
and again the farther it is rotated the faster the machine moves in reverse. Maximum
speeds in both directions are restricted to safe limits and between forward and
reverse is a stable neutral band where there is no travel speed. Steering is accomplished
simply by tilting down the appropriate end of the handlebar. If the handlebar is
not rotated, so there is no travel speed, but one end of the handlebar is tilted
down, one potentiometer will be moved forwardly and the other one in reverse, which
will cause one drive wheel to turn forward and the other one backward. The machine
can thus be turned on its own center if desired without any forward or reverse
travel. This gives a more responsive maneuverability than many previous machines
of this class have had.
Simultaneously rotating and tilting the handlebar will result in
differential movements of the potentiometers that will cause both drive motors
to turn in the same direction, but one will turn faster than the other. This combination
of travel speed and steering will produce a gradual turn in either forward or
reverse travel direction as selected by the operator.
The handlebar is secured to the machine frame through its central
pivot bracket so the operator may, if he or she wishes, apply a manual force in
any direction to the machine by pushing equally on both ends of the handlebar in
the selected direction. This will not affect the rotation or the tilt that the
operator has set into the handlebar, so will have no effect on the controlled speed
and steering. However, it will supplement the power steering and add substantially
to the natural feel of handling the machine.
Other objects will appear from time to time in the ensuing drawings
Brief Description of the Drawings
Description of the Preferred Embodiment
- Fig. 1 is a side view showing a person operating a floor scrubber which utilizes
the present invention.
- Fig. 2 is a schematic perspective assembly drawing of the system for controlling
speed and steering of the scrubber of Fig. 1 showing the preferred embodiment of
- Fig. 3 is a schematic diagram of the electrical circuit and the traction drive
of the scrubber.
- Fig. 4 illustrates a control technique for making a left turn during forward
- Fig. 5 illustrates an alternative control technique for making a left turn
during forward travel.
- Fig. 6 is a side view, partly in section, of Fig. 2.
The present invention will be described as applied to a floor scrubber,
although it is also applicable to other types of machines such as, for example,
floor sweepers. The scrubber may be similar to conventional scrubbers now available
except for the improved control system which is the subject of this invention.
As seen in Fig. 1, the operator walks behind the scrubber, which is identified
by the number 10, and controls its speed and steering by placing one or both hands
on the hand grips 12 of a straight transverse handlebar which is situated at the
rear of the machine and at a convenient height.
The mechanical construction of this control system is shown in Fig.
2. The handlebar 14 is made of one continuous piece of round steel tubing and is
fitted at its ends with hand grips 12. The handlebar has a long centerline 16.
Two bushings 18 (only one shown) rotatably support the handlebar in steering yoke
20. There is a mounting bracket 22 which is bolted or otherwise secured to the
structure of the scrubber. Steering yoke 20 is pivotally attached to bracket 22
by pivot pin 24, which is held in place by cotter pins through cross holes drilled
through it near its ends. By this construction handlebar 14 is thus allowed to
rotate about its long centerline 16 and also pivot about an axis established by
pivot pin 24.
Two handlebar arms 26 and 28 are secured to handlebar 14 by set screws
(not shown). These arms have integral hubs which surround the handlebar and prevent
it from sliding endwise through steering yoke 20. A dual throw coil spring 30,
similar to those used in door knobs, is mounted about handlebar 14 and is arranged
to always return it to a predetermined stationary position. This action effectively
places the machine speed control in neutral.
Handlebar 14 and steering yoke 20 can be pivoted about pivot pin
24 by applying a force on one of the hand grips 12 in a direction perpendicular
to pivot pin 24. If no such force is applied, the handlebar and steering yoke will
be held in a centered, horizontal position by neutral centering arm 32. This component
is a plastic bar attached to centering arm support 34, which in turn is pivotally
attached to mounting bracket 22 by pin 36.
In Fig. 2, for clarity of illustration, there is some space shown
between neutral centering arm 32 and steering yoke 20. In normal service, however,
the neutral centering arm is resiliently pressed against the under side of the
steering yoke by compression spring 38, acting through push rod 40. This rod has
a reduced diameter 42 which fits loosely in a hole in centering arm support 34.
The diameter of the opposite end of rod 40 is also reduced enough so that a nut
44 can be run onto a threaded portion 46 of the push rod. Push rod 40 slides freely
through a hole in a bulkhead in the scrubber frame, shown fragmentally at 48.
Spring 38 is compressed between the bulkhead and nut 44, which can be set to compress
the spring as desired.
When the operator wishes to pivot the handlebar about pivot pin 24
he or she may exert a force on one of the hand grips 12 in a direction perpendicular
to the pivot pin. This will move down one end of the steering yoke 20, which will
in turn push down the centering arm 32 and further compress spring 38. When the
operator releases the force on the hand grip the spring pushing up on neutral centering
arm 32 will push steering yoke 20 back to level and restore the handlebar to its
neutral position. This effectively places the steering control in neutral.
There are two potentiometers 50 and 52 mounted in two mounting brackets
54. These brackets are attached to the structure of the scrubber. The potentiometers
have control arms 56 and 58 associated with them. These arms pass through slots
59 in the mounting brackets, the ends of the slots serving to define the amount
of rotation available to the handlebar and potentiometers. There are two links 60
and 62 which have conventional ball joints on their ends. These links connect the
handlebar arms 26 and 28 with the potentiometer control arms 56 and 58.
Fig. 3 shows a schematic diagram of the electrical circuit and the
traction drive of the scrubber. The machine is powered by a battery pack indicated
at 64. The drive wheels 66 and 68 are driven by two electric motors 70 and 72 through
two chain and sprocket drives indicated generally at 74. The drive wheels are
mounted on two independent coaxial drive axles 76 and 77, each of which is rotatably
supported by two sealed ball bearings 78 mounted on the structure of the scrubber.
The two motors 70 and 72 are controlled by two motor controllers 80 and 82. These
may be commercially available units such as, for example, those offered by Curtis
PMC of Dublin, California. The two motor controllers in turn are controlled by
the two potentiometers 50 and 52. The motor controllers are so designed that a
mid-range voltage from a potentiometer causes zero rotation of the controlled motor,
while voltages below the mid-range will cause motor rotation in one direction and
voltages above the mid-range will cause motor rotation in the other direction. The
farther the voltage values move from mid-range, the faster the controlled motor
will turn. Thus this control system will provide the machine with variable speed
forward travel, neutral, and variable speed reverse travel simply by moving the
two potentiometers through their range. There is no need for external switches
to provide neutral or reverse.
Fig. 3 shows the left potentiometer 52 controlling the right motor
controller 80 and drive wheel 66, and the right potentiometer 50 controlling the
left motor controller 82 and drive wheel 68. This arrangement will result in a
steering response as shown in Fig. 4, where a downward push on the left hand grip
during forward travel will produce a left turn. An alternative arrangement is possible,
by not crossing the wires shown crossed in Fig. 3, but instead connecting the right
potentiometer 50 to the right motor controller 80 and the left potentiometer 52
to the left motor controller 82. This will give a steering response as shown in
Fig. 5, where a downward push on the right hand grip during forward travel produces
a left turn. Both arrangements are possible, and either one can be used without
affecting the novel aspects of the invention. It should be pointed out that for
either arrangement, if a left turn is to be made when the machine is traveling
in reverse, it will be necessary to push down the opposite hand grip that the one
that is pushed down for a left turn when traveling forward. Also, it should be
apparent that right turns can be made in either arrangement and in either forward
or reverse travel by pushing down the opposite hand grip than is pushed down for
a left turn.
It has been found that the steering is most comfortable when angle
"A" in Fig. 1 is between 30 and 45 degrees. However, any angle between 0° and 90°
can be used. As shown in Fig. 6, pivot pin 24 will lie at right angles to the selected
angle. Handlebar arms 26, 28 in their neutral positions should be set parallel
to pivot pin 24. The potentiometer brackets 54 should be located so that in neutral
the ball jointed links 60, 62 will form right angles with both the handlebar arms
26, 28 and the potentiometer arms 56, 58 and the potentiometer arms are in the
middle of the slots 59 in the brackets 54.