US3747326A

US3747326A - Clock drive with piezoelectric tuning fork

Info

Publication number: US3747326A
Application number: US00162227A
Authority: US
Inventors: W Heywang; M Guntersdorfer
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1970-07-17
Filing date: 1971-07-13
Publication date: 1973-07-24
Anticipated expiration: 1990-07-24
Also published as: CH987271A4; DE2035587A1; GB1353176A; AT315082B; NL7109410A; FR2099428A5; IT997021B

Abstract

A clock drive in which a piezoelectric tuning fork actuates the driving wheel of a clockwork includes a second tuning fork serving as a narrow-band, frequency-determined time standard coupled with the wheel-actuating tuning fork.

Description

United States Patent [1 1 Heywang et al.

[ July 24, 1973 ;1i.s.- Cl.....

CLOCK DRIVE WITH PIEZOELECTRIC TUNING FORK inventors: WalterHeywang, Neuke ferloh; Max

Guntersdorier, Munich, both of Germany Siemens Aktiengesellscliait, Berlin and Munich, Germany. 7

Filed: July 13, 1971 Appl. No.: 162,227

Assignee:

Foreign Application Priority Data July 17, 1970 Germany P 20 35 587.7

58/23 TF Int. Cl G040: 3/00 Field of Search 58/23 R, 23 TF, 23 A;

1 References Cited UNITED STATES PATENTS 1/1912 Reefman 58/23 TF x 1,849,271 3/1932 Bower 58/23 TF UX 2,015,410 9/1935 Prescott 58/23 TF UX 3,207,965 9/1965 Lavet 58/23 TF'X 3,579,974 5/1971 Schmidt 58/23 TF FOREIGN PATENTS OR APPLICATIONS 1,539,922 8/1968 France 58/23 TF 1,523,958 7/1969 Germany... 58/23 TF 1,809,223 6/1970 Germany 58/23 A 5/1965 Great Britain 58/23 TF Primary.Examiner-Richard B. Wilkinson Assistant Examiner.lolm F. Gonzales Attorney-Carlton Hill et a1.

[57] ABSTRACT A clock drive in which a piezoelectric tuning fork actuates the driving wheel of a clockwork includes a second tuning fork serving as a narrow-band, frequencydetermined time standard coupled with the wheelactuating tuning fork.

23 Claims, 2 Drawing Figures PATENTEL 3.747. 326

I SHEEI 1 OF 2 av ATTYS.

. CLOCK DRIVE WITH PIEZOELECTRIC TUNIN FORK This invention relates to a frequency-stabilized clock drive, and is more particularly concerned with driving force as generated by a piezoelectric tuning fork operating as an oscillator.

A principal purpose of the present invention is to improve clock driving means especially in battery-driven smallclocks in which a piezoelectrically excitable tuning fork has a part of the resonance oscillation energy transferred by means of a transmission pawl or the like to a drive wheel by which the hands of the clock are driven through a suitable gearwork. While it is known that the deflection of a piezoelectric bending element can be increased by constructing it of a plurality of individual laminations which are polarized in opposite directions so that upon electrical excitation at a predetermined voltage level the deflection is greater than with a simple bent strip, the adaptation of such a plural lamination element device in a clockwork has presented certain difficulties and problems in the attainment of satisfactory frequency control in respect to the resonance oscillations of the clock drive fork.

An important object of the present invention is to overcome the foregoing and other disadvantages, defects, inefficiencies, shortcomings and problems in prior clock drives of this type and to attain important advantages and improvements in the operation of piezoelectric tuning fork clock drives. 7

Another object of the invention is to provide a new and improved piezoelectric tuning fork clock driving system. g

A further object of the invention is to provide new and improved means 'for controlling the frequency constancy of a piezoelectric tuning fork oscillator in a clock drive.

Still another object of the invention is' to provide a new and advantageous electrical clock drive attaining unusual driving ability with low battery voltage.

, Yet another object of the invention is to .provide a clock drive of the character-indicated which is unusually stable under variable temperature conditions.

A still further object of the invention is to provide a new andimproved clock drive embodying a plurality of cooperative piezoelectric devices.

A yetfurther object of the invention is to provide a simplified transmission of oscillatory to rotary driving movement in piezoelectric tuning fork clock drives.

Other objects,featuresand advantages of the invention willbe readily apparent from the following description of a preferred embodiment thereof, taken in conjunction with the accompanying drawings, although variations and modifications may be effected without departing from the spirit and scope of the novel concepts embodied in the disclosure, and in which:

FIG. 1 is a schematic illustration representing one practical embodiment of the invention; and

FIG. 2 is a performance curve diagram.

In FIG. 1 is shown a representative clock drive with means for maintaining frequency and oscillation amplitude constant according to the present invention. For this purpose a tuning fork Aserving as the principal driving means has its prongs coupled vibrationally and mounted on a mounting block -I. Advantageously, the

prongs of the fork A comprise respective pairs of ceramic laminations 2 and 3 having opposite piezoelectric effect of different or opposite polarization. Thereby, with the electrodes in a suitable identical arrangement, the individual laminations are switched electrically parallel, but in respect to their mechanical effect one behind the other, so that, in spite of low voltage, a great deflection results. Although the laminations may be adhesively connected, where they are superficially metallized they may be welded to each other. I

In order to attain a frequency-stabilized clock drive with the piezoelectric tuning fork A and to attain frequency constancy and oscillation of the fork A only on its basic frequency, a second, smaller tuning fork Z is provided and coupled mechanically and/or acoustically to the fork A and serves as a narrow-band, frequencydetermined time standard. The fork Z is desirably made of a material relatively unaffected by temperature, and more particularly made of metal, so that its resonance frequency is unaffected by temperature in contrast to the fork A which may be affected in its resonance frequency by temperature variations.

Optimum frequency-selective properties of the tuning forks in the oscillator circuit are utilized by a preferred electrical coupling, wherein the right-hand prong of the tuning fork A, as visualized in FIG. 1, is connected in the collector circuit of a transistor Tr, while the left-hand prongof the fork A and the frequencyand amplitude-determined fork member Z and a coil S are in the base circuit of the transistor Tr and thus in the reverse-coupling branch of the oscillator. By means of an inductor coil L the collector circuit of the transistor Tr is completed via the battery B in a directcurrent manner, while the working point of the transistor is adapted to be adjusted with the assistance of aresistor R. Coupling between the tuning fork A and the tuning fork Z is effected by means of a coupling resistance R I In order to attain desirable corresponding basic frequency in the two tuning forks, disregarding their upper frequencies, and prevent any harmful reverse effect of the tuning fork A onto the oscillation of the tuning fork Z, with substantial freedom from damping of oscillations of the freely-oscillating ends of the fork Z, the fork Z comprising a metallic oscillator 4, carries on the oscillating ends of its prongs respective loading weights 5 and piezoelectric transducers 6. The weights 5 may serve as respective electrical connections, as shown.

Simple and efficient means are provided for translating the driving oscillations of the fork A into rotary motion for the clockwork mechanism, i.e. the usual'hour and minute hands and the gearing for coordinating movement of thosehands. To this end, oscillation en- -ergy of the tuning fork A is transferred from the right prong thereof by means herein comprising a mechanical transmission mechanism coupled directly therewith, i.e. a pawl 7 extending therefrom to and engaging the perimeter of a drive wheel 8. Advantageously, instead of gear teeth on the wheel with which the pawl must mesh, the wheel perimeter is made of a suitable wear-resistant plastic material of sufficient softness and resilience such that the driving tip of the pawl digs into the wheel perimeter when the pawl is thrust toward the wheel in the fork oscillations to thus cause the wheel to rotate a predetermined increment. As the pawl is retracted its tip slides over the surface of the wheel which is held against reverse rotation during such retraction movement of the pawl. This is a substantially more economical driving coupling between the pawl and the drive wheel than a toothed arrangement of the wheel requiring a costly attachment of formation of teeth to the wheel.

According to the present invention there are, further, provided means for generating electrical signals in the rotation of the drive wheel 8 fed into the oscillator in such a manner that the amplitude of the driving tuning fork A and thus the speed of rotation of the drive wheel 8 are maintained constant. Measurement of the speed of the drive wheel 8 applied for regulation of the oscillation amplitude is adapted to be effected without physical contact between relatively moving parts. To this end, the drive wheel 8 and the coil S are desirably cooperative as an alternating current generator. For this purpose, the wheel 8 is provided with electric signal producing areas 9 located equidistantly spaced along or adjacent to its circumference, equal in number with the desired oscillation frequency of the oscillator A. In one form, the areas 9 may be, as shown, narrow spaced radially elongated, comprising, respective magnetic layers of alternating polarity. Thereby, as each of the areas 9 moves in the field of the coil S, the coil detects the respective area and a respective electrical impulse is effected, resulting in the induction of an electrical alternating current voltage in the coil S as the wheel 8 rotates. At the desired speed, the frequency of this voltage corresponds exactly to the frequency of the time standard oscillator Z. In order to couple back, the sum of the voltages which are supplied by the time standard fork Z and by the coil S is applied. The result is a simple regulator circuit involving switching the coil electrically in line with'the frequency-determining tuning fork Z whereby a phase-correct addition of the voltages produced in both switching elements is enabled in a simple manner.

Instead of a coil such as S, a field plate or similar magnetic-field responsive component may be utilized. Other structuresin the signal producing areas 9 may be employed, such as piezoelectric layers of alternating polarization to produce a corresponding signal in a suitable receiver which reacts to changing electrical fields. Further, due to the electrical areas 9, a non-magnetic behavior of the clock is assured.

Operation of the regulated clock drive is as follows. When the battery B is connected in the circuit, the right-hand prong of the driving oscillator fork A is deflected, and due to its elastic properties starts to oscillate. These oscillations are transferred vibrationally to the left-hand prong of the fork A by way of the mounting block 1 and produce a voltage which is transferred by means of the coupling resistor R onto the righthand prong of the time standard fork Z. By means of the vibrational coupling of the tuning fork prongs of the fork Z, a voltage is produced in the left piezoelectric transformer 6 which is checked against the voltage formed in the coil S, and serves the purpose of switching on and off the transistor Tr. The voltages are conducted in such a manner that the transistor Tr is switched on and off at the correct moment.

' The effect of the amplitude stabilization with the aid of the coil 8 and the signal areas 9 is as follows. One may proceed most simple from a state in which the amplitudes and frequencies of the voltage is formed in the coil S and in the time standard fork Z are equal. HOW, ever, a phase difference of 180 may exist. Thus, the

two voltages neutralize each other, the transistor Tr is not switched, and no voltage affects the drive oscillator fork A. Oscillation amplitude of the fork A and thus the speed of the wheel 8 will diminish until the phase difference has changed to the extent that the resulting reverse-coupling voltage is just sufficient to maintain the correct speed of rotation of the wheel 8. It is important that the wheel 8 have enough operational mass to bridge the delays in reaction due to the oscillator quality of the fork A. Further, it is advantageous not to provide too great resonance quality for the tuning fork A.

It is helpful to refer to FIG. 2 which assists in explaining a further advantage arising from a low oscillator quality of the fork A. Thus, there is represented by D the oscillation amplitude of the two tuning forks A and Z, in dependence on the frequency f. F is the narrowband excitation function of the time standard fork Z, and F is the broad-band excitation function of the tuning fork A. At a certain temperature, the resonance frequenciesf, of the two tuning forks coincide. If the resonance frequency of the ceramic tuning fork A (the tuning fork Z being temperature compensated) shifts as is shown by, the curve F' only a small amplitude difference occurs, represented by AD with a broadband resonance curve of the driving oscillator A, whereby this amplitude difference, depending on the temperature, is the smaller the more broad-banded the resonance curve of the driving oscillator A becomes.

If a common toothed wheel is provided instead of the tooth-less plastic perimeter wheel 8 illustrated in FIG. 1, the coil S can, of course, be omitted. The voltage which is formed in the left-hand prong of the time standard fork Z is then directly coupled to the basic circuit of the transistor Tr.

Other amplifying elements may be employed instead of the bipolar transistor Tr, such as field-effect transistors, bipolar transistors in a Darlington switch, or the like, without departing from the present invention. The individual voltages which are generated in the coil S or in the left prong of the time-standard fork Z may also be amplified first, if necessary. To avoid too high a cur rent consumption, skillful selection of the individual component parts should be practiced.

It will be understood that variations and modifications may' be effected without departing from the spirit and scope of the novel concepts of this invention.

We claim as our invention:

1. In a frequency-stabilized clock drive including a piezoelectric tuning fork which transfers oscillation energy by means of a mechanical transmission mechanism directly coupled therein to a drive wheel and is connected in an oscillator circuit including an electrical energy supplying battery, the improvement comprising:

a narrow-band, frequency-determined time standard oscillator tuned to thebasic oscillation frequency of said tuning fork; and

means operatively coupling said oscillator with the tuning fork.

2. A clock drive according to claim 1, wherein said v oscillator comprises a second, smaller tuning fork made 4. A clock drive according to claim 1, wherein the prongs of said tuning fork comprise laminations made of ceramic material with opposite piezoelectric effect.

5. A clock drive according to claim 1, wherein the prongs of said tuningfork co'mpris e laminations with opposite polarization.

6. A clock drive according to claim 1, wherein the prongs of said tuning fork comprise laminations which are secured to one another in each of the prongs.

7. A clock drive according to claim 1, wherein one prong of the tuning fork is connected to said transmission mechanism, said oscillator comprises a smaller tuning fork, a second prong of 'said driving tuning fork being electrically coupled with one prong of said smaller tuning fork, and the remaining prong of said smaller tuning fork being coupled in the electrical circuit with said battery.

8. A clock drive according to claim 1, wherein one prong of the tuning fork is connected to said transmission, said oscillator comprises a smaller tuning form, a second prong of said driving tuning fork being electrically coupled with one prong of said smaller tuning fork, an alternating current generator including said wheel and a coil, and said coil being connected at one end in said electrical circuit with said battery and at its opposite end connected with the remaining prong of said smaller tuning fork.

9. A clock drive according to claim 1, including an alternating current generator comprising said wheel and a coil, and means electrically connecting said coil with said oscillator.

10. A clock drive according to claim 9, said wheel having circumferentially spaced signal producingareas numerically correlated to the driving oscillations of said tuning fork.

11. A clock drive according to claim 10, wherein said areas comprise magnetic layers of alternating polarity.

12. A clock drive according to claim 10, wherein said areas comprise piezoelectric layers of alternating polarization. v g 13. A clock drive according to claiml, including an alternating current generator including a coilswitched electrically in series'with said oscillator, and electrical signalling means carried by said wheel and cooperatively related to said coil in the rotation of the wheel. 5 14. A. clock drive according to claim '1, wherein said wheel has a resiliently yieldable plastic perimeter, and said transmission comprises a pawl attached to said tuning fork and having a driving tip which bites into the wheelperimeter for driving the wheel rotatably in each driving oscillatorymovement and slides over the wheel piezoelectric tuning fork which transfers oscillationena narrow-band, frequency-determined time standard oscillator tuned to the basic oscillation frequency v of said tuning fork; and means operatively coupling said oscillator with the tuning fork;

said oscillator comprising a second, smaller tuning fork made of metal and carrying piezoelectric transducers and additional weights at its free oscillating. ends. 17. In a frequency-stabilized clock drive including a piezoelectric tuning fork which transfers oscillation en ergy by means of a transmission mechanism to a drive wheel and is connected in an oscillator circuit including coupled in the electrical circuit with said battery.

18. In a frequency-stabilized clock drive including a piezoelectric tuning fork which transfers oscillation en-. ergy by means of a transmission mechanism to a drive wheel and is connected in an oscillator circuit including an electrical energy supplying battery, the improvement comprising:

a narrow-band, frequency-determined time standard oscillator tuned to the basic oscillation frequency of said tuning fork; 1 means operatively coupling said oscillator with the tuning fork; one prong of said tuning fork being connected to said transmission; a said oscillator comprising a smaller tuning fork; a second prong of said driving tuningfork being electrically coupled with one prong of said smaller tuning fork; an alternating current generator including said wheel and a coil; and 1 i said coil being connected at one end in said electrical circuit with said battery and at its opposite end connected with the remaining prong of said smaller tuning fork. 19. In a frequency-stabilized clock drive including a piezoelectric tuning fork which transfers oscillation energy by means of a transmission mechanism to a drive wheel and is connected in an oscillator circuit including an electrical energy supplying battery, the improvement comprising:

a narrow-band, frequency-determined time standard oscillator tuned to the basic oscillation frequency of said tuning fork;

means operatively coupling said oscillator with the tuning fork;

an alternating current generator comprising said wheel and a coil; and

means electrically connecting said coil with said oscillator.

20. In a frequency-stabilized clock drive including a piezoelectric tuning fork which transfers oscillation energy by means of a transmission mechanism to a drive wheel and is connected in an oscillator circuit including an electrical energy supplying battery, the improvement comprising:

means operatively coupling said oscillator with the tuning fork;

an alternating current generator including a coil switched electrically in series with said oscillator; and

electrical signalling means carried by said wheel and cooperatively related to said coil in the rotation of the wheel.

21. In a frequency-stabilized clock drive including a piezoelectric tuning fork which transfers oscillation energy by means of a transmission mechanism to a drive wheel and is connected in an oscillator circuit including an electrical energy supplying battery, the improvement comprising:

means operatively coupling said oscillator with the tuning fork;

said wheel having a resiliently yieldable plastic perimeter; and

said transmission comprising a pawl attached to said tuning fork and having a driving tip which bites into the wheel perimeter for driving the wheel rotatably in each driving oscillatory movement and slides over the wheel perimeter during retraction oscillatory movement.

22. In a frequency-stabilized clock drive including a piezoelectric tuning fork which transfers oscillation energy by means of a mechanical transmission mechanism to a drive wheel and is connected in an oscillator circuit including an electrical energy supplying battery, the improvement comprising:

said wheel having a resiliently yieldable plastic perimeter; and

23. A clock drive according to claim 22, wherein said oscillator circuit includes an oscillator operatively coupled with said tuning fork, electric signal producing area's regularly spaced circumferentially on said wheel by means of which the speed of rotation of the wheel can be measured, and a device stimulated by said areas in the rotation of the wheel to generate an electrical signal transmitted to said oscillator whereby the amplitude of the tuning fork and the speed of the drive wheel are maintained constant.

Claims

1. In a frequency-stabilized clock drive including a piezoelectric tuning fork which transfers oscillation energy by means of a mechanical transmission mechanism directly coupled therein to a drive wheel and is connected in an oscillator circuit including an electrical energy supplying battery, the improvement comprising: a narrow-band, frequency-determined time standard oscillator tuned to the basic oscillation frequency of said tuning fork; and means operatively coupling said oscillator with the tuning fork.

2. A clock drive according to claim 1, wherein said oscillator comprises a second, smaller tuning fork made of metal and carrying piezoelectric transducers and additional weights at its free oscillating ends.

3. A clock drive according to claim 1, wherein said tuning fork and said oscillator are electrically coupled together.

4. A clock drive according to claim 1, wherein the prongs of said tuning fork comprise laminations made of ceramic material with opposite piezoelectric effect.

5. A clock drive according to claim 1, wherein the prongs of said tuning fork comprise laminations with opposite polarization.

7. A clock drive according to claim 1, wherein one prong of the tuning fork is connected to said transmission mechanism, said oscillator comprises a smaller tuning fork, a second prong of said driving tuning fork being electrically coupled with one prong of said smaller tuning fork, and the remaining prong of said smaller tuning fork being coupled in the electrical circuit with said battery.

10. A clock drive according to claim 9, said wheel having circumferentially spaced signal producing areas numerically correlated to the driving oscillations of said tuning fork.

12. A clock drive according to claim 10, wherein said areas comprise piezoelectric layers of alternating polarization.

13. A clock drive according to claim 1, including an alternating current generator including a coil switched electrically in series with said oscillator, and electrical signalling means carried by said wheel and cooperatively related to said coil in the rotation of the wheel.

14. A clock drive according to claim 1, wherein said wheel has a resiliently yieldable plastic perimeter, and said transmission comprises a pawl attached to said tuning fork and having a driving tip which bites into the wheel perimeter for driving the wheel rotatably in each driving oscillatory movement and slides over the wheel perimeter during retraction oscillatory movement.

15. A clock drive acording to claim 14, including electric signal producing areas regularly spaced circumferentially on said wheel by means of which the speed of rotation of the wheel can be measured, and a device stimulated by said areas in the rotation of the wheel to generate an electrical signal transmitted to said oscillator whereby the amplitude of the tuning fork and the speed of the drive wheel are maintained constant.

16. In a frequency-stabilized clock drive including a piezoelectric tuning fork which transfers oscillation energy by means of a transmission mechanism to a drive wheel and is connected in an oscillator circuit including an electrical energy supplying battery, the improvement comprising: a narrow-band, frequency-determined time standard oscillator tuned to the basic oscillation frequency of said tuning fork; and means operatively coupling said oscillator with the tuning fork; said oscillator comprising a second, smaller tuning fork made of metal and carrying piezoelectric transducers and additional weights at its free oscillating ends.

17. In a frequency-stabilized clock drive including a piezoelectric tuning fork which transfers oscillation energy by means of a transmission mechanism to a drive wheel and is connected in an oscillator circuit including an electrical energy supplying battery, the improvement comprising: a narrow-band, frequency-determined time standard oscillator tuned to the basic oscillation frequency of said tuning fork; means operatively coupling said oscillator with the tuning fork; one prong of said tuning fork being connected to said transmission mechanism; said oscillator comprising a smaller tuning fork; a second prong of said driving tuning fork being electrically coupled with one prong of said smaller tuning fork; and the remaining prong of said smaller tuning fork being coupled in the electrical circuit with said battery.

18. In a frequency-stabilized clock drive including a piezoelectric tuning fork which transfers oscillation energy by means of a transmission mechanism to a drive wheel and is connected in an oscillator circuit including an electrical energy supplying battery, the improvement comprising: a narrow-band, frequency-determined time standard oscillator tuned to the basic oscillation frequency of said tuning fork; means operatively coupling said oscillator with the tuning fork; one prong of said tuning fork being connected to said transmission; said oscillator comprising A smaller tuning fork; a second prong of said driving tuning fork being electrically coupled with one prong of said smaller tuning fork; an alternating current generator including said wheel and a coil; and said coil being connected at one end in said electrical circuit with said battery and at its opposite end connected with the remaining prong of said smaller tuning fork.

19. In a frequency-stabilized clock drive including a piezoelectric tuning fork which transfers oscillation energy by means of a transmission mechanism to a drive wheel and is connected in an oscillator circuit including an electrical energy supplying battery, the improvement comprising: a narrow-band, frequency-determined time standard oscillator tuned to the basic oscillation frequency of said tuning fork; means operatively coupling said oscillator with the tuning fork; an alternating current generator comprising said wheel and a coil; and means electrically connecting said coil with said oscillator.

20. In a frequency-stabilized clock drive including a piezoelectric tuning fork which transfers oscillation energy by means of a transmission mechanism to a drive wheel and is connected in an oscillator circuit including an electrical energy supplying battery, the improvement comprising: a narrow-band, frequency-determined time standard oscillator tuned to the basic oscillation frequency of said tuning fork; means operatively coupling said oscillator with the tuning fork; an alternating current generator including a coil switched electrically in series with said oscillator; and electrical signalling means carried by said wheel and cooperatively related to said coil in the rotation of the wheel.

21. In a frequency-stabilized clock drive including a piezoelectric tuning fork which transfers oscillation energy by means of a transmission mechanism to a drive wheel and is connected in an oscillator circuit including an electrical energy supplying battery, the improvement comprising: a narrow-band, frequency-determined time standard oscillator tuned to the basic oscillation frequency of said tuning fork; means operatively coupling said oscillator with the tuning fork; said wheel having a resiliently yieldable plastic perimeter; and said transmission comprising a pawl attached to said tuning fork and having a driving tip which bites into the wheel perimeter for driving the wheel rotatably in each driving oscillatory movement and slides over the wheel perimeter during retraction oscillatory movement.

22. In a frequency-stabilized clock drive including a piezoelectric tuning fork which transfers oscillation energy by means of a mechanical transmission mechanism to a drive wheel and is connected in an oscillator circuit including an electrical energy supplying battery, the improvement comprising: said wheel having a resiliently yieldable plastic perimeter; and said transmission comprising a pawl attached to said tuning fork and having a driving tip which bites into the wheel perimeter for driving the wheel rotatably in each driving oscillatory movement and slides over the wheel perimeter during retraction oscillatory movement.

23. A clock drive according to claim 22, wherein said oscillator circuit includes an oscillator operatively coupled with said tuning fork, electric signal producing areas regularly spaced circumferentially on said wheel by means of which the speed of rotation of the wheel can be measured, and a device stimulated by said areas in the rotation of the wheel to generate an electrical signal transmitted to said oscillator whereby the amplitude of the tuning fork and the speed of the drive wheel are maintained constant.