US3654408A - Differential-motion timer - Google Patents

Abstract

A differential-motion timer. Reciprocating motion of a predetermined frequency and angular displacement is converted into unidirectional rotary motion by means of at least two ratchet wheels coaxially aligned and independently free-wheeling and each having a different number of notches. Each of the ratchet wheels is driven by a ratchet drive which is connected to the reciprocating element. Accordingly, each ratchet wheel can convert reciprocating motion to unidirectional rotary motion, the speed of the rotary motion being, on the average, proportional to the driver frequency. Since each of the ratchet wheels has a different number of notches, it follows that each of the wheels will be driven at a slightly different speed by the single ratchet driver. This difference speed is the timing motion and the relative angular positions of the wheels correspond to the elapsed time. A switch is actuated whenever certain preselected corresponding points on each of the ratchet wheels arrive at predetermined positions.

Description

United States Patent Meek [54] DIFFERENTIAL-MOTION TIMER [72] Inventor: James M. Meek, 1600 Atwood Road, Silver Spring, Md. 20906 [22] Filed: Apr. 30, 1970 [21] App1.No.: 33,457

[52] U.S. Cl ..200/33 R, 200/35 R, 200/43, 335/123 [51] Int. Cl. ..H0lh 43/18 [58] Field of Search ..200/38 B, 38 F, 153 LB, 33,

[56] References Cited UNITED STATES PATENTS 2,010,570 8/1935 Stein ..200/43 X 2,452,747 11/1948 Gomez ..200/43 2,578,347 12/1951 Gagnaire ..200/35 R 2,614,181 10/1952 Consalvi et a1. .200/153 P X 2,978,552 4/1961 Russell ..200/33 R 3,090,843 5/1963 Hall 200/38 F 3,239,614 3/1966 Simmons... 200/38 B 3,015,003 12/1961 Simmons ..200/38 B [451 Apr. 4, 1972 [57] ABSTRACT A differential-motion timer. Reciprocating motion of a predetermined frequency and angular displacement is converted into unidirectional rotary motion by means of at least two ratchet wheels coaxially aligned and independently freewheeling and each having a different number of notches. Each of the ratchet wheels is driven by a ratchet drive which is connected to the reciprocating element. Accordingly, each ratchet wheel can convert reciprocating motion to unidirectional rotary motion, the speed of the rotary motion being, on the average, proportional to the driver frequency. Since each of the ratchet wheels has a different number of notches, it follows that each of the wheels will be driven at a slightly different speed by the single ratchet driver. This difference speed is the timing motion and the relative angular positions of the wheels correspond to the elapsed time. A switch is actuated whenever certain preselected corresponding points on each of the ratchet wheels arrive at predetermined positions.

1 1 Claims, 1 Drawing Figure DIFFERENTIAL-MOTION TIMER THE RIGHTS OF THE GOVERNMENT governmental purposes without the payment to me of any royalty thereon.

BACKGROUND OF THE INVENTION This invention relates to timers in general, and more particularly to an electromechanical timer having a high degree of resolution and capable of withstanding high acceleration forces.

Timers for use in high acceleration environments are often subjected to strict and demanding specification requirements. Such timers must, for example, be capable of operating in projectiles spinning at up to 360 rps, consume only a few milliwatts of low frequency (100 Hz) power and must be accurate to one part in l or better. Prior art electrically driven clocks having their own mechanical time base in the form of a torsion pendulum do not meet the stringent requirements outlined above. Many prior art timers require the use of a motion rectifier such as a ratchet plus a gear train in order to convert the oscillating motion produced in the torsion resonator to rotary motion of the desired speed. The use of a separate motion rectifier in conjunction with a complex gear train to provide the desired output speeds renders such timers highly inaccurate and inefficient particularly under the high acceleration conditions referred to above.

It is, therefore, the primary object of this invention to provide an electromechanical timer which does not require a separate motion rectifier and speed reducer.

Another object of the invention is to provide an electromechanical timer which does not require the use of gears or a gear train in order to achieve the desired timing speed.

Another object is to provide a timer using solid figures of revolutions for its moving components.

Still another object of the invention is to providea timer which is accurate and rugged under high acceleration conditions. 1

SUMMARY OF THE INVENTION Briefly, in accordance with this invention, reciprocating motion of a predetermined frequency and angular displacement is converted into unidirectional rotary motion by means of at least two ratchet wheels coaxially aligned and independently free-wheeling and each having a different number of notches. Each of the ratchet wheels is driven by a ratchet drive which is connected to the reciprocating element. Accordingly, each ratchet wheel can convert reciprocating motion to unidirectional rotary motion, the speed of the rotary motion being, on the average, proportional to the driver frequency. Since each of the ratchet wheels has a different number of notches, it follows that each of the wheels will be driven at a slightly different speed by the single ratchet driver. This difference speed is the timing motion and the relative angular positions of the wheels correspond to the elapsed time. A switch is actuated whenever certain preselected corresponding points on each of the ratchet wheels arrive at predetermined positions.

BRIEF DESCRIPTION OF THE DRAWING The FIGURE is an exploded perspective view of one embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the FIGURE, oscillator provides AC power to drive-coil 11 which in turn sets up a magnetic filed within core'piece l2 and across core gap 13. A permanent magnet 14 is secured within torsion wheel 15 and is located within core gap 13. Leaf spring 17 is positioned on shaft 16 such that the initial angular wheel position of wheel 15 results in a small lateral displacement between the poles of the permanent magnet and the electromagnet. This offset provides for self-starting. When the electromagnet is momentarily energized by means of source 10, either attraction or repulsion will occur depending upon the relative polarity of the magnets. As the magnetic filed alternates, attraction and repulsion of permanent magnet 14 causes torsion wheel 15 to oscillate in increasing amplitude until it stabilizes at an amplitude where in put energy per cycle equals losses per cycle. With normal amplitude the magnet swings over the center of the gap once for each cycle of AC current. Accordingly this results in one mechanical stroke or one half mechanical cycle per electrical oscillation. Thus, for a Hz input the wheel frequency will be 50 Hz. In order to provide small adjustments in the natural frequency of torsion wheel 15, leaf spring 17 is held within the yoke 19 of frequency adjust lever 18. Accordingly, the resonator may be tuned to match the frequency of the electrical oscillator. Maximum amplitude of wheel 15 will occur when the frequencies are matched and resonance is achieved.

The amplitude of displacement of torsion wheel 15 is a function of the magnitude of the voltage at source 10 and tends to increase with increasing voltage. Additionally, under high acceleration conditions the pivot friction at shaft 16 tends to increase considerably thereby tending to reduce the amplitude of angular displacement. These variables on the amplitude of displacement of torsion wheel 15 are undesirable. Accordingly, in order to provide a reciprocating motion having a constant amplitude of displacement and constant frequency, a second reciprocating element, amplitude limiting wheel 21, is provided. Amplitude limiting wheel 21 is driven at a constant angular displacement and constant frequency whenever the first reciprocating element, torsion wheel 15, exceeds a predetermined minimum displacement. Amplitude limiting wheel 21 is driven by torsion wheel 15 by means of a rod 20 which is secured to torsion wheel 15 at a predetermined distance from its axis and extends into an open groove 23 located at the perimeter of the amplitude limiting wheel 21. The amplitude limiting wheel has a predetermined limited angular displacement or as shown in the Figure. This is provided by means of amplitude limiting shaft locks (not shown) which are placed at opposite ends of the desired angular stroke. Torsion wheel 15, on the other hand, is not limited in its angular rotation. Accordingly, as torsion wheel 15 oscillates beyond a predetermined minimum amplitude, amplitude limiting wheel 21 traverses the predetermined angle until the appropriate shaft locks prevent further rotation. At that point rod 20 disengages from groove 23 permitting torsion wheel 15 to continue to rotate with rod 20 outside of groove 23. When torsion wheel 15 reverses its direction rod 20 re-engages groove 23, thereby driving amplitude limiting wheel 21 in the reverse direction. This process is repeated at the other end of the stroke. Thus, it can be seen that reciprocating element 21 is limited to a predetermined angular displacement whenever reciprocating element 15 exceeds a certain predetermined angular displacement. Accordingly, element 2] reciprocates at a substantially constant frequency and angular displacement.

The reciprocating motion of amplitude limiting wheel 21 is converted to unidirectional rotary motion by means of a plurality of ratchet wheels. Referring again to the Figure, ratchet wheels 28 and 29 are coaxially aligned on shaft 24 and are independently free wheeling. Each of the ratchet wheels has a slightly different number of notches. Although only two ratchet wheels are shown, a plurality of ratchet wheels may be employed. Ratchet drive-pawl 25 is secured to reciprocating wheel 21 by means of screw 26. A pin 27, also secured to wheel 21, causes drive pawl 25 to press against the notches of wheels 28 and 29. As reciprocating wheel 21 rotates in a forward direction drive pawl 25 engages a notch in each of ratchet wheels 28 and 29, thereby driving each of the ratchet wheels a distance of one notch in a forward direction (as shown in the Figure). When reciprocating wheel 21 rotates in its reverse direction, ratchet wheels 28 and 29 remain stationary being secured by a stationary securing ratchet 30 which is held in place by suitable pins 31 and 32. Accordingly, it will be appreciated that the reciprocal motion of wheel 21 is converted to continuous rotary motion in ratchet wheels 28 and 29.

The angular speed of the two ratchet wheels will differ slightly due to the different number of notches in each wheel. Assuming, for example, that ratchet wheel 28 has 100 teeth and ratchet wheel 29 has 101 teeth, it follows that wheel 28 will complete a full revolution prior to wheel 29, although both ratchet wheels will remain proportional to the drivefrequency of reciprocating element 21. The difference speed of these two ratchet wheels is the timing motion and the relative angular positions of the ratchet wheels at any given time will correspond to the elapsed time. It will be noted that drive pawl 25 is shown as a bifur-cated element. This is a preferred arrangement, not a requirement.

The elapsed time referred to above may be measured in any number of ways depending upon particular requirements. One way would involve the use of an electro-optical switch as shown in the Figure. Slits or holes 35 and 36 are provided in each of ratchet wheels 28 and 29, respectively, and a light beam produced at light source 33 is directed through both slits and detected by photodetector 34 whenever the two slits align. Photodetector 34 may be any conventional detector whose output voltage or resistance changes in response to light. This change can in turn cause the operation of a relay switch (not shown). The time required for alignment of the slits will depend upon the relative angular speed of the two ratchet wheels and this in turn will depend upon the relative number of notches in each of the ratchet wheels as well as the input frequency at source 10. With the use of more than two ratchet wheels the total time required for alignment of all slots and therefore actuation of the photoelectric switch can be considerably extended. Thus, with an input frequency of 100 Hz the described arrangement would achieve alignment in 202 seconds at increments of milliseconds. This could be achieved with a timing accuracy of one part per thousand. With the use of additional ratchet wheels having different numbers of teeth the time period for full alignment is the produce of the total number of teeth and time per stroke. Additionally, each ratchet wheel may be provided with a plurality of slots, the slots being scattered along the radium of each of the ratchet wheels, and a plurality of photoelectric sources and detectors aligned with the slots for actuating various functions at predetermined times. These variations would be within the skill of the ordinary worker in the art.

While an optical switch has been illustrated, it is but one of a number of different switching systems which may be used to sense the alignment of two or more predetermined points on each of the ratchet wheels. An alternative switch may comprise an insulated conducting rivot located on each ratchet wheel and a plurality of leaf-spring electrical contacts. As the two wheels rotate, each rivot would make electrical contact with a pair of leaf springs for each revolution. The switch would be actuated when both rivots align at predetermined positions, thereby causing the leaf-springs to make a single continuous electrical contact. Still another switching arrangement may comprise the use of electrical rivets on each of the ratchet wheels with the use of commutator leafs connected to each of the ratchet wheels for completing an electrical circuit when the two rivets align.

It should be noted that the above-described arrangement of ratchet wheels has the effective output gear ratio of 100 to l and 101 to 1 without using gears. in conventional prior art designs such a gearing ratio would have required at least a two or three-pass gear train consisting of four or six additional gears in addition to a motion rectifier to achieve the same result.

In order to avoid the effects of increased pivotal friction as a result of high acceleration forces it has been found advantageous to utilize homogeneous solid figures of revolution such as cylinders and spheres as the components of the system. The utilization of solid figures of revolution significantly reduces the effects of coriolis, centripetal and linear acceleration torques. In this connection it will be noted that the reciprocating elements 15 and 22 as well as ratchet wheels 28 and 29 are in the form of solid figures of revolution. Permanent magnet 14 can be made of material whose density matches that of wheel 15 in order to maintain homogeneity.

Deformation of the elements under the effects of high acceleration can also be reduced by scaling down proportionally all dimensions of the system. Thus, the effects of stress and deflection be significantly reduced by micro-miniaturization. Proportional scaling down can also reduce both the pivot friction torque and the friction caused by inertial reaction forces. It has been found, for example, that a decrease in the scale factor by n results in a decrease in pivot friction by n. In addition to these techniques it may be desirable to employ such well known techniques as surface polishing and the use of solid lubricants in order to reduce the coefficient of friction at high load conditions. These latter techniques are all within the skill of the art.

The timing resolution or minimum time increment corresponds to one stroke of the drive pawl or twice the period of the drive oscillator. The accuracy will depend on the stability of the electronic oscillator when the resonator is connected to follow the oscillator. However, the resonator can be driven electrically by conventional feedback means (not shown) so that the resonator acts as a mechanical time base and the accuracy is essentially that of the resonator.

Setting the predetermined time interval may be accomplished by cycling the mechanism forward an amount which is the difference between the desired time interval setting and the total possible running time. This is necessary since the clock cannot conveniently be run backward to this setting. To set, it is necessary first to run the clock until slots 35 and 36, for example, coincide and then count forward from this initial condition. Other obvious setting means may be provided by those skilled in the art.

I wish it to be understood that I do not desire to be limited to the exact details of construction shown and described for obvious modifications will occur to a person skilled in the art.

I claim as my invention:

1. A differential motion timer comprising:

a. means for providing reciprocating motion having a predetermined frequency and angular displacement;

b. at least two ratchet wheels coaxially aligned and independently free wheeling, each of said ratchet wheels having a different number of notches;

c. ratchet drive means connected to said means for providing reciprocating motion to drive each of said ratchet wheels in a forward direction; and

d. means for actuating a switch whenever selected corresponding points on each of said ratchet wheels arrive at predetermined positions.

2. The timer of claim 1 wherein said means for providing reciprocating motion comprises:

a. a first reciprocating element;

b. means for driving said first reciprocating element to exceed a predetermined minimum angular displacement;

c. a second reciprocating element; and

d. means for driving said second reciprocating element at a constant angular displacement whenever said first reciprocating element exceeds its predetermined minimum displacement.

3. The timer of claim 2 wherein each of said first and second reciprocating elements comprises a solid figure of revolution.

4. The timer of claim 2 wherein said means for driving said first reciprocating element comprises:

a. means for establishing an alternating magnetic field;

b. a permanent magnet for driving said first reciprocating element in response to the force created by said magnetic field.

5.'The timer of claim 4 further comprising means for adjusting the angular displacement of said first reciprocating element.

6 The timer of claim 3 wherein said means for driving said second reciprocating element comprises a rod secured to said first reciprocating element at a predetermined distance from its axis and extending into a groove located within said second reciprocating element.

7. The timer of claim 1 switch comprises:

a. at least one transparent portion in each of said ratchet wheels;

b. at least one source of light directed so as to transmit a light path through said transparent portions; and

c. means or detecting said light and actuating a switch whenever corresponding transparent portions align within said light path.

wherein said means for actuating a 8. The timer of claim 1 wherein said ratchet drive means comprises a bifurcated pawl having a number of prongs equal to the number of ratchet wheels.

9. The timer of claim 1 further comprising ratchet holding means to prevent each of said ratchet wheels from rotating in the reverse direction.

10. The timer of claim 1 wherein the time required for actuating said switch is determined by the produce of the total number of teeth on each of said ratchet wheels and the time period for each stroke of said ratchet drive.

11. The timer of claim 6 wherein said rod is secured perpendicular to the plane defined by said first reciprocating element.

Claims (11)

1. A differential motion timer comprising: a. means for providing reciprocating motion having a predetermined frequency and angular displacement; b. at least two ratchet wheels coaxially aligned and independently free wheeling, each of said ratchet wheels having a different number of notches; c. ratchet drive means connected to said means for providing reciprocating motion to drive each of said ratchet wheels in a forward direction; and d. means for actuating a switch whenever selected corresponding points on each of said ratchet wheels arrive at predetermined positions.

2. The timer of claim 1 wherein said means for providing reciprocating motion comprises: a. a first reciprocating element; b. means for driving said first reciprocating element to exceed a predetermined minimum angular displacement; c. a second reciprocating element; and d. means for driving said second reciprocating element at a constant angular displacement whenever said first reciprocating element exceeds its predetermined minimum displacement.

3. The timer of claim 2 wherein each of said first and second reciprocating elements comprises a solid figure of revolution.

4. The timer of claim 2 wherein said means for driving said first reciprocating element comprises: a. means for establishing an alternating magnetic field; b. a permanent magnet for driving said first reciprocating element in response to the force created by said magnetic field.

5. The timer of claim 4 further comprising means for adjusting the angular displacement of said first reciprocating element.

6. The timer of claim 3 wherein said means for driving said second reciprocating element comprises a rod secured to said first reciprocating element at a predetermined distance from its axis and extending into a groove located within said second reciprocating element.

7. The timer of claim 1 wherein said means for actuating a switch comprises: a. at least one transparent portion in each of said ratchet wheels; b. at least one source of light directed so as to transmit a light path through said transparent portions; and c. means or detecting said light and actuating a switch whenever corresponding transparent portions align within said light path.

8. The timer of claim 1 wherein said ratchet drive means comprises a bifurcated pawl having a number of prongs equal to the number of ratchet wheels.

9. The timer of claim 1 further comprising ratchet holding means to prevent each of said ratchet wheels from rotating in the reverse direction.

10. The timer of claim 1 wherein the time required for actuating said switch is determined by the produce of the total number of teeth on each of said ratchet wheels and the time period for each stroke of said ratchet drive.

11. The timer of claim 6 wherein said rod is secured perpendicular to the plane defined by said first reciprocating element.

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