The present invention relates to a mechanical clock, and,
more particularly, to correcting the time displayed by a mechanical clock.
BACKGROUND OF THE INVENTION
The analog mechanical clock had been a staple in automobiles
for years prior to the advent and popularity of digital clocks. A problem with such
analog clocks is that they suffered from notoriously inaccurate time keeping. The
analog clock is typically driven by a stepper motor whose operation is governed
by a relatively low frequency crystal oscillator. The instability of such low frequency
oscillators may result in inaccuracy in time keeping of plus or minus four seconds
per day. Another problem with analog clocks that they constantly drew a relatively
large current from the vehicle's battery.
The digital clock, often included as a feature in the radio,
has better time keeping accuracy and lower current draw than an analog clock. The
microprocessor-based digital clock may use a higher frequency crystal oscillator
that is more stable than the lower frequency oscillators that must be used with
stepper motors. The higher stability of the oscillator results in more accurate
time keeping, with a level of inaccuracy of only about 0.25 second per day. A problem
with a digital clock, however, is that it may limit the styling options for the
design of the passenger compartment of the vehicle. Moreover, a digital clock does
not spatially indicate time of day, as does an analog clock. Thus, reading time
from a digital clock may require slightly more cognitive activity by the driver,
and may distract the driver from the task at hand, i.e., driving the vehicle.
Vehicle designers and consumers have expressed an interest
in reviving the use of analog clocks in modem day vehicles. However, today's consumers
will not tolerate the inaccurate time keeping associated with previous generations
of mechanical clocks.
What is needed in the art is a mechanical clock for use
in an automobile that has the same level of time keeping accuracy that is associated
with digital clocks.
SUMMARY OF THE INVENTION
The present invention provides a mechanical clock arrangement
that senses the time of day displayed by a mechanical clock and moves the hour hand
and/or minute hand to more correctly display an actual time of day. The actual time
of day may be received from a digital processor, as with a digital clock, or may
be received from some air-borne signal, such as a radio signal or a global positioning
system (GPS) signal.
The invention comprises, in one form thereof, a mechanical
clock arrangement including a linkage apparatus rotatingly driving an hour hand
and/or a minute hand of a mechanical clock. A sensing device senses a time of day
displayed by the mechanical clock. A control device is in communication with both
the sensing device and a source of an actual time of day. The control device actuates
the linkage apparatus to thereby cause the time of day displayed by the mechanical
clock to correspond to the actual time of day.
The invention comprises, in another form thereof, a method
of operating a mechanical clock, including sensing a time of day displayed by the
mechanical clock. The sensing is performed by a sensing device. An actual time of
day is received in electronic form. A linkage apparatus of the mechanical clock
is actuated to thereby cause the time of day displayed by the mechanical clock to
correspond to the actual time of day. The actuating is performed by a control device.
An advantage of the present invention is that the time
of day displayed by the mechanical clock is more accurate than with previous mechanical
clocks used in automotive applications.
Another advantage is that the standby current may be greatly
reduced by disabling the clock while the key is out of the ignition.
Yet another advantage is that there is no need for pin
hole controls as typically required with known mechanical clocks.
A further advantage is that the time of day displayed by
the mechanical clock may be automatically set based upon an actual time of day received
from an external source, such as a GPS signal or a radio signal.
BRIEF DESCRIPTION OF THE DRAWINGS
The above-mentioned and other features and objects of this
invention, and the manner of attaining them, will become more apparent and the invention
itself will be better understood by reference to the following description of embodiments
of the invention taken in conjunction with the accompanying drawings, wherein:
DESCRIPTION OF THE PREFERRED EMBODIMENTS
- Figure 1 is a schematic diagram of one embodiment of a mechanical clock arrangement
of the present invention.
- Figure 2a is an enlarged view of the hour gear and associated contacts of the
arrangement of Figure 1.
- Figure 2b is a schematic representation of the hour gear and associated contacts
of Figure 2a.
- Figure 3 a is another enlarged view of the hour gear and associated contacts
of the arrangement of Figure 1 wherein the hour gear is in a position approximately
six hours removed from the position of Figure 2a.
- Figure 3b is a schematic representation of the hour gear and associated contacts
of Figure 3a.
- Figure 4 is a flow chart of one embodiment of a method of operating a mechanical
clock of the present invention.
- Figure 5a is an enlarged view of another embodiment of an hour gear and associated
contacts that may be used in a mechanical clock arrangement of the present invention.
- Figure 5b is a schematic representation of the hour gear and associated contacts
of Figure 5a.
- Figure 6a is another enlarged view of the hour gear and associated contacts
of Figure 5a wherein the hour gear is in a position approximately six hours removed
from the position of Figure 5a.
- Figure 6b is a schematic representation of the hour gear and associated contacts
of Figure 6a.
- Corresponding reference characters indicate corresponding parts throughout the
several views. Although the drawings represent embodiments of the present invention,
the drawings are not necessarily to scale and certain features may be exaggerated
in order to better illustrate and explain the present invention. The exemplifications
set out herein illustrate embodiments of the invention in several forms and such
exemplification is not to be construed as limiting the scope of the invention in
The embodiments discussed below are not intended to be
exhaustive or limit the invention to the precise forms disclosed in the following
detailed description. Rather, the embodiments are chosen and described so that others
skilled in the art may utilize their teachings.
Referring now to the drawings, and particularly to FIG.
1, there is shown one embodiment of a mechanical clock arrangement 10 of the present
invention including a mechanical clock 12, a sensing device 14 for sensing a time
of day displayed by clock 12, a source 16 of an actual time of day, and a control
device 18. Clock 12 includes an hour hand 20, a minute hand 22, and a linkage 24
for rotatingly driving hands 20, 22. Linkage 24 includes an hour gear 26 that is
fixed to hour hand 20, and a minute gear 28 that is fixed to minute hand 22
Sensing device 14 includes potentiometers 27a, 27b electrically
connected to electronic circuitry 29 and respectively associated with hour gear
26 and minute gear 28. Potentiometer 27a includes an arcuate resistive element 30,
best shown in Figure 2A, having two opposite ends 32, 34 electrically connected
to respective annular terminals 36, 38 via respective connectors 40, 42, which may
be in the form of connecting traces. Element 30 and terminals 36, 38 may be affixed
to hour gear 26 such that terminal 36 is disposed radially outward of element 30,
and terminal 38 is disposed radially inward of element 30.
Terminals 36, 38 and connectors 40, 42 may be formed of
an electrically conductive material, such as copper, that has substantially no electrical
resistance. Element 30 may be formed of an electrically resistive substance such
that element 30 has a measurable resistance between ends 32, 34. In one embodiment,
the measurable resistance is approximately between 1000 and 20,000 ohms. Further,
the resistivity of element 30 may be substantially consistent throughout the arc
formed thereby such that there is an equal resistance across any two sections of
the same size within the arc. In one embodiment, element 30 is formed of a resistive
ink that may be screen printed on gear 26.
Potentiometer 27a also includes three contacts in the form
of wipers 44, 46 and 48 slidingly engaged with terminal 36, resistive element 30
and terminal 38, respectively. Wiper 44 may be electrically grounded via a ground
line 50. A constant DC voltage from circuitry 29 may be applied to wiper 48 via
a power line 52. In one embodiment, the constant DC voltage is approximately between
two volts and twenty volts. A microcontroller 54 may receive a scaled down voltage
that is representative of the voltage applied to wiper 48. More particularly, through
a voltage divider including resistors 56, 58, an input 60 of microcontroller 54
may receive a scaled down version of the voltage applied to wiper 48. Another input
62 of microcontroller 54 may receive, through a line 64 and a voltage divider including
resistors 66, 68, a scaled down version of the voltage at wiper 46.
Resistive element 30 is shown in the drawings as forming
an arc of approximately 350 degrees. Generally, the resistive element may form an
arc of greater than 330 degrees. The span of the arc may be limited such that a
gap 70 between ends 32, 34 is larger than a width 72 of wiper 46. Thus, wiper 46
is prevented from possibly providing a short circuit between ends 32, 34.
The structure of potentiometer 27b is substantially similar
to that of potentiometer 27a as described above. Thus, in order to avoid needless
repetition, the structure of potentiometer 27b is not described in detail herein.
Actual time of day source 16 includes a time keeper section
74 within microcontroller 54. Time keeper 74 may include a high frequency crystal
oscillator (not shown), and may be similar to time keeping units in conventional
digital clocks. Time keeper 74 may be connected to a set time user interface 76
through which a user may initially set a time of day that time keeper 74 may thereafter
increment and maintain. Interface 76 may be in the form of an hour button and a
minute button, or may be in the form of one or more dials, as is well known.
In an alternative embodiment, the source of the actual
time of day may be a radio frequency receiver 78 that is in communication with controller
54. Receiver 78 may receive a radio frequency signal that includes time of day information.
The radio frequency signal may be in the form of a GPS signal, Satellite Digital
Audio Receiver (SDAR) signal, Digital Audio Broadcast (DAB) signal, In Band On Channel
(IBOC) signal, Vehicle Information and Communication System (VICS) signal, Data
Audio Channel (DARC) signal, FM radio signal, AM radio signal, FM-RDS signal, FM-RDBS
signal, television signal, or cell phone signal, for example. In the case of a GPS
signal, microcontroller 54 may receive not only the time of day, but may also be
able to determine through the GPS capabilities what time zone the automobile is
Control device 18 is in communication with both sensing
device 14 and actual time of day source 16. Control device 18 includes microcontroller
54, a memory device 80 in communication with microcontroller 54, and control circuitry
82 for controlling a stepper motor driver 84, which, in turn, drives a stepper motor
86. Stepper motor 86 is coupled to linkage 24, as indicated by dashed line 88, such
that stepper motor 86 may rotate gears 26, 28 and thereby also cause hands 20, 22
to rotate. Stepper motor driver 84 includes a low frequency crystal oscillator 90
that enables motor 86 to drive clock 12 at a time rate of speed that is nearly accurate,
but, as discussed above, may be off by approximately 4 seconds per day.
In operation, an output resistance of potentiometer 27a
depends upon a rotational position of gear 26. Potentiometer 27a may have two output
resistances, i.e., a resistance between wipers 44, 46 being a first output resistance,
and a resistance between wipers 46, 48 being a second output resistance. A sum of
these two output resistances may be constant, i.e., the resistance of element 30
between ends 32, 34. The rotational position of gear 26 determines where along arcuate
element 30 that wiper 46 makes contact, and this position determines how the end-to-end
resistance of element 30 is divided between the first and second output resistances
of potentiometer 27a. Thus, both a first resistance between terminal 36 and wiper
46 and a second resistance between terminal 38 and wiper 46 are dependent upon a
rotational position of gear 26.
Given that a known DC voltage is applied to end 34 of element
30, and end 32 is grounded, the voltage at wiper 46 on line 64 is indicative of
the rotational position of gear 26 and hand 20. This voltage at wiper 46 and the
known resistance between ends 30, 32 indirectly indicate the resistance between
wipers 44, 46, as well as the resistance between wipers 46, 48. The relationship
between the rotational position of gear 26 and the ensuing voltage at wiper 46 may
be empirically predetermined and stored in memory 80. Alternatively, a desired predetermined
relationship between the rotational position of gear 26 and the ensuing voltage
at wiper 46 may be created by laser trimming element 30 or by some other resistance
adjustment technique. This desired and predetermined relationship between the rotational
position of gear 26 and the ensuing voltage at wiper 46 may also be stored in memory
Figure 2B illustrates schematically how element 30 is set
up as a potentiometer, with wipers 44, 46, 48 functioning as the three terminals
of the potentiometer. Figure 3A illustrates gear 26 in a second position approximately
six hours removed from the position depicted in Figure 2A. That is, in Figure 3A,
gear 26 and hour hand 20 are rotated approximately 180 degrees from their position
in Figure 2A. In Figure 2A, wiper 46 is closer to end 32 than to end 34, and thus
the voltage at wiper 46 may be closer to the ground voltage at end 32 than to the
DC voltage applied at end 34. In Figure 3A, in contrast, wiper 46 is closer to end
34 than to end 32, and thus the voltage at wiper 46 may be closer to the DC voltage
applied at end 34 than to the ground voltage at end 32. The movement of wiper 46
along element 30 between Figures 2A and 3A is represented in Figures 2B and 3B as
movement of wiper 46 along the schematically indicated resistor 30. More particularly,
wiper 46 is disposed at point 90 on element 30 in Figures 2A and 2B, and is disposed
at point 92 on element 30 in Figures 3A and 3B.
The resistive ink that forms element 30 may be laser trimmed
to improve the accuracy or consistency of the resistance of element 30. Whether
by laser trimming or by some other resistance adjustment technique, desired relationships
may be created between the output resistances of potentiometers 27 and the time
of day displayed by mechanical clock 12. Moreover, relationships between the resistances
between terminals 36, 38 and wiper 46 may be empirically predetermined, or predetermined
via some resistance adjustment technique.
Figure 4 illustrates a method 400 of the present invention
for operating a mechanical clock. In a first step S402, a time of day displayed
by mechanical clock 12 is sensed by sensing device 14. For example, by measuring
the voltage at wiper 46 with respect to the ground voltage at wiper 44, and by measuring
the voltage at the corresponding wiper in potentiometer 27b with respect to the
grounded wiper in potentiometer 27b, sensing device 14 may determine the time of
day displayed by clock 12. A predetermined relationship between the voltages at
the wipers and the time of day displayed on clock 12 may be retrieved from memory
80 in determining what displayed time of day corresponds to the voltages being read
at the wipers. In a next step S404, an actual time of day is received in electronic
form. More particularly, control device 18 may receive an actual time of day from
time keeper 74. Alternatively, control device 18 may receive an actual time of day
from receiver 78, wherein the actual time of day is carried in some radio frequency
signal received by receiver 78. In a final step S406, a linkage apparatus of the
mechanical clock is actuated by a control device to thereby cause the time of day
displayed by the mechanical clock to correspond to the actual time of day. For example,
control device 18 may actuate linkage 24 to thereby cause the time of day displayed
by clock 12 to correspond to the actual time of day.
Control device 18 may compare the displayed time of day
to the actual time of day to determine by how much hands 20, 22 need to be incremented
or decremented to display the actual time of day. Microcontroller 54 may then transmit
signals to stepper motor driver 84 via circuitry 82 to thereby cause stepper motor
86 to increment or decrement gears 26, 28 and respective hands 20, 22 to the actual
time of day.
In order to simplify the illustration, stepper motor 86
is shown in Figure 1 as being directly coupled to gears 26, 28. However, it is to
be understood that linkage 24 may include one or more intermediate gears between
stepper motor 86 and hour gear 26 and minute gear 28.
Another embodiment of a potentiometer 127 that may be used
in a mechanical clock arrangement of the present invention is illustrated in Figure
5A. Instead of having two terminals on opposite ends of a resistive element, as
with potentiometers 27a, 27b, potentiometer 127 has only a single terminal 138 electrically
connected to an end 134 of arcuate resistive element 130. An opposite end 132 of
element 130 is open circuited. Although potentiometer 127 is shown in Figure 5A
as being attached to an hour gear 126 fixed to an hour hand 120, potentiometer 127
is also suitable for attachment to a minute gear.
A wiper 146 is slidingly connected to element 130. A DC
voltage may be applied to wiper 146 via a power line 152. In one embodiment, the
voltage may be approximately between two volts and twenty volts. A second wiper
148 is slidingly connected to terminal 138. Wiper 148 may be connected to ground
potential through a resistor 149 and a ground line 150. In one embodiment, the resistance
of resistor 149 may be close to the resistance of element 130, e.g., approximately
between 1000 and 20,000 ohms. The voltage at wiper 148 may be measured by a microcontroller
(not shown) via line 164 and possibly via associated circuitry (not shown).
As hour gear 126 rotates, the arcuate span between end
134 and wiper contact 146 changes, thereby changing the resistance between wipers
146, 148. The combination of the resistance between wipers 146, 148 and resistor
149 forms a voltage divider for dividing the V+ voltage at power line 152. Thus,
the measured voltage at line 164 also varies with the rotation of gear 126, and
the rotational position of gear 126 may be ascertained by examining the voltage
at line 164.
Figure 5B illustrates schematically how element 130 is
set up as a potentiometer, with wipers 146, 148 functioning as two of the three
terminals of the potentiometer. Figure 6A illustrates gear 126 in a second position
approximately six hours removed from the position depicted in Figure 5A. That is,
in Figure 6A, gear 126 and hour hand 120 are rotated approximately 180 degrees from
their position in Figure 5A. In Figure 5A, wiper 146 is closer to end 132 than to
end 134, and thus the voltage at wiper 146 will be closer to the V+ voltage at end
132 than to the scaled voltage applied at end 134. In Figure 6A, in contrast, wiper
146 is closer to end 134 than to end 132, and thus the voltage at wiper 146 will
be closer to the DC voltage applied at end 134 than to the ground voltage at end
132. The movement of wiper 146 along element 130 between Figures 5A and 6A is represented
in Figures 5B and 6B as movement of wiper 146 along the schematically indicated
resistor 130. More particularly, wiper 146 is disposed at point 190 on element 130
in Figures 5A and 5B, and is disposed at point 192 on element 130 in Figures 6A
Resistive element 130 and resistor 149 conjointly form
a voltage divider, with element 130 being connected to V+ voltage and resistor 149
being connected to ground voltage. However, in another embodiment (not shown), a
voltage divider is formed by element 130 being connected to ground voltage and resistor
149 being connected to V+ voltage. Moreover, although potentiometer 127 is set up
such that wiper 146 is at a higher voltage than wiper 148, it is also possible to
set up the potentiometer such that wiper 148 is at a higher voltage than wiper 146.
Other details of the structure and function of potentiometer
127 are substantially similar to those of potentiometer 27a as disclosed above,
and thus are not described in detail herein.
While this invention has been described as having an exemplary
design, the present invention may be further modified within the spirit and scope
of this disclosure. This application is therefore intended to cover any variations,
uses, or adaptations of the invention using its general principles. Further, this
application is intended to cover such departures from the present disclosure as
come within known or customary practice in the art to which this invention pertains.