CA1297429C - Clutch/damper - Google Patents

Abstract

ABSTRACT
A clutch/damper for isolating and absorbing vibration induced reactive torques from adversely affecting a motor drive system. A friction plate variably engages a gear coupled to the drive motor and to a load mass to permit normal drive in the absence of excessive reactive torque forces and to allow the motor to continue to drive against a slipping load in the presence of excessive reactive torque forces. Feedback is employed in the drive system to compensate for the small errors induced by the slippage. A position sensor responsive to an angular position of the load provides an error signal to an amplifier, which drives the motor in a direction to align the angular orientation of the drive motor and load mass, thereby reducing the error signal to a null value. When applied to drive a moveable platform of a radar apparatus housing a receiver/transmitter and antenna, the invention substantially decouples the platform from the drive motor when reactive forces exceed an allowable level.

Description

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CLUTCH/DAMPER :~
BACKGROI~Q~VENTIQN ~ ~ :
l. Field of the,~lnvention .
The in~ntion relates generally to shock and ::
vibration isolators, and:more particularly to a .
~ clutch/damper~for isolating the oscillatory reactive : forces of a driven mass from the driving motor.

2. Description of the Prior Art There are many applications in which energy from a drive motor i8 applied through a gear train to drive a load mass and wherein, when subjected to environmental vibrations, the mass exhibits reactive forces which are coupled through the gear train and adversely affect the driving motor. When the system resonates, r~eactive:~
torques are induced in the driving motor which may cause the motor ~to stall or actually be driven backwards.
igh reliabil1ty stepper motors have been commonly applied for drive systems because they are relatively inexpensive and the drive system electronics are less :20 complex than for alternating current or DC current variable speed~motors. It has been found, however,,that for a given motor~siz~e, less drive torque is available : ; than with correspvn,ding~alternating current~or direct ~ 24 current motcrsr and the speed-torque characteristics of :: ~ : ~ : : ; : :

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the stepper motors are not as advantageous. In order to over~ome the presence of the reactive tor~ues, the prior art applied a frictional damper in parallel with ~he drive system or simply utilized a grossly increased in size drive motor to over-power the feedback torque. These solutions have the disadvantage tha~ the use of larger motors, which are ln themselves a component of the suspended mass, increases the driven mass, thereby aggravating the problem, and a parallel friction damper requires additional motor torque to overcome the friction.
The present invention overcomes the disadvantages of the prior art by decoupling the load mass from the drlving motors when the reaction torques axceed a predetermlned level, and by allowing the load mass to be driven by the drive motors when the reaction torques are less than the predetermined level.
SUMMARY OF THE INVENTION
In accordance with the present invention there is provided an apparatus for control of angular reaction torques applied by a motor-driven mass to a drive motor, comprising: input means coupled to said motor and adapted for rotary motion about a first axis, drive means having first and second substantially coplanar radially disposed frickion faces and adapted for rotary motion about a second axis, output means adapted for rotary motion ; about said second axis and coupled to energize said driven mass, wherein said output means comprises an axial shaft having a plate affixed laterally thereto, said plate having a substantially planar radially disposed face, rotatably engaging said first ~ace of said drive means, energy absorbing means for coupling said . , ~æ974Z9 drlve m~ans to said output means, said energy absorbing means allowing free transfer to gaid outpu~ means of rotary energy applied to said drive means by said input means so long as a predetermined sllp torque is not exceeded, and for absorbing : transfer of energy stored in said driven mass to sald input means ~hen said predetermined slip torque is exceeded, and positional feedback means including a sensor coupled to said driven mass for providing a control signal representative of an angular position of said driven mass to said drive motor and motive power means responæive to said control signal for incr~mentally positioning ~aid drive motor so as to re~tore the relative angular posltions of said output means with respect to ~ald input means when said driven maæs ls angularly displaced by said rea~tive tor~ue, said energy absorbing means cooperating in series relationship with said feedback means and with said drive means and said output means to provide clutch means for damping excurslons of said drive motor and coupling of rea~tive torgues ~etween said drive motor and said drlven mass in excess of a predetermined value.
In accordance wlth the present invention there ls also provlded an apparatus for control of angular reaction torques applled by a motor-driven mass to a drive motor, compxlsing, lnput means coupled to said motor and adapted for rotary motion about a first axls, drive means adapted for rotary motion about a s~cond axls, output means adapted for rotary motion about said second axls and coupled to energize said driven massr wherein said output means comprises an axial shaft having a pla~e affixed laterally thereto, said plate having a substantially planar radlally ,~

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disposed face, energy absorbing means for couplin~ said drive means to said output means, said energy absorbing means allo~ing free transfer to said output means of rotary ~nergy applied to said drive means by said input means so long as a predetermined slip torque i5 not exceeded and for absorbing ~ransfer of energy stored in said driven mass to said input means when said predetermined slip torque is exceeded, said energy absorbing means further comprising reslllent means for providing a substantially sinusoidal restoring torque for maintaining the relative angular positions of said output means with respect to ~aid input mean~, said input means ~urther aomprisiny first gear means, ~aid drive means further comprising second ~ear means meshed with sald fir~t gear means and having first and second radially extending substantially planar faaes, said energy absorbing means comprising first and second diskoidal bodies of elastomeric material, said first body disposed between said planar face of said plate and said first planar face of said second gear means, further comprising backing plate means, comprising a substantially rigid planar plate distally mounted on said axial shaft from said plate and said driven mass, said second body of elastomeric material disposed between said backing plate means and said second planar face of said second gear means, means for affixing said first body of elastomeric material to said planar face of said plate of sald axial shaft and to said first planar face of said drive means, and means for affixlng said second body of elastomeric material to said backing plate means and said second planar face of said drive means, so that sald input means resiliently engages said driven ~297429 mass, and said drive means is rotatably displaced with respect ~o said output means whan subjected to a reactive torque from said driven ma~s, wherehy said input means is substantlally dlsengaged from said driven mass when said reaction tor~ue exceeds a predetermined value, and said input mean~ is sub~tantially engaged to said drlve mas~ when said reaction torque is less than said predetermined value, whereby said ~irst and second bodies o~
~lasto~er material urge said output means to rotate at the same angular velocity and relative angular displacement as said drive means when said reactive torgue ls disslpated.
In acaordance wlth the pre#ent iuven~lon there is further provided an apparatus for control o~ angulax reaction torques applied by a motor-driven mass to a drlve motor, comprisingt input means coupled to said motor and adapted for ::
rotary motion about a first axis, drive means having first and second substantially coplanar radlally disposed friction faces and adapted for rotary motion about a second axis, output means adapted for rotary motlon about said second axis and coupled to energize said driven mass, ~herein said output means comprlses an axial shaft havlng a fric~ion plate afflxed laterally thereto, said plate having a substantially planar radially disposed ~ace, ; rotatably engaging said first face of said drive means, energy absorbing means for coupling said drive means to said output means, said energy absorbing means allowing free transfer to said output means of rotary energy applied to said drlve means by said input means ~o long as a predetermined slip torque is not exceeded, and for absorbing transfer of energy stored in sald ':

' ' ~2~4~g driven mass to said inpu~ means when said predetermined torque is exceeded, said input means fur~her comprising first gear means, said drive means ~urther comprising second gear means meshed with said first gear means and having a flrst substantially planar face and a second face having an inclined surface with respect to said planar face, said surface having a contour varying in spiral fashion from a predetermined minimum dimension at the circumference of said second gear means ~o a predetermined maximum dimension at said second axis, ramp disk means haviny a first face with an inclined sur~aae having a contour subs~antially coincident with said inclined surface of said second cJear means, the conkour of sald ramp disk means varying in spiral fashion from a predetermined maximum dimension at said circumference to a predetermined minimum dimension at said second axis, said ramp disk means transversely slidable upon said axial sha~t and fixed for angular rotation coincident with said shaft, and spring : compression means ~or applying a predetermined compressive force to said ramp disk means for urging said inclined surface of said ramp disk means in frictional contact with said inclined surface of said second gear means, so that said ramp disk is axially displaced on said axial shaft when said reactive torque exceeds a predetermined value, thereby allowing substantially free rotation : of said driven mass with respect to said input means~ and said ramp disk is frictionally engaged w1th said second gear means when said reaction tor~ue is less than said predetermined value, thereby tending to urge said output means to substantlally identlcal angular velocity and displacement with respect ~o said A

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The present invention in~erposes a clutch/damper element to absorb momentary reaction torques exceeding a predefined motor torque limit and thereby permits the utilization o~ low cost, high reliability, conventional stepper motor drive systems~ It is adapted for use between the gear reduction train of the drive and the driven mass. In a preferred configurationr the vibration energy is dissipated by the generation of frictional energy. In a iurther preferred embodiment, a torsional member in the clutch/damper provides absorption o~ at leas~ a portion of the vibration energy, whlle restoring the relative positions of the drive shaft and driven mass when the reaction torque subsldes.
The present invention comprises a first member coupled to a motor and adapted for rotary motion. A drive member is coupled to the first member and rotates about an axis. An energy absorbing member is coupled between the drlving member and an output shaft forwardly transferring the driving force to the driven mass so long as a predetermined slip torque is not exceeded. At a predetermined value of slip torque, the energy absorbing member, resiliently coupled to the driving member and the output member, permits rotation of the driving member between friction surfaces, thereby limiting the torque back-driven to the motor to the predetermined slip torque.
In a further preferred embodiment, the energy absorbing member comprises a pair of elastomeric bodies bonded to the driven member and the output shaft to permit resilient coupling of the first member to the driven ~ass when the allowable reaction torque A

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6b 72519-16 is exceeded. Upon dissipation of the react$on torque, the resilient body causes the drive member in the ou~put sha~t to be aligned to corresponding angular posi~ions.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a pictorial repre~entation in plan view of a radar sy~tem employing a gear train to angularly displace a receiver/transmitter platform.
Figure ~ ls a schematic representation in block form of a mechaniaal drive æyste~ including a clutch~damper of the present inventlon.
Figure 3 is a view ln cross-section o~ a prqierred embodiment o~ the pre~ent lnvention employing a iriction disk.
; Figure 4 is a view ln cros~-section o~ a ~urther preferred embodiment employing an elastomer toxque energy absorbing disk.
Figure 5 i5 a view in cross-section of a still further preferred embodiment employing a spring/ramp configuration as the I
energy absorbing member.
Eigure 6 is a view of the assembled clutch damper according to the present invention.
Figure l exemplifies th^ problem as applied to a radar apparatus. A ba~e 10 houæes the electronic~ for driving an a~imuth ~motor and gear traln 18 an~ elevation motor and gear train 22, and other electronics. The base 10 ~s supported against a vertical wall 14 by vibration and shock lsolators 12. An azimuth support s~ructure 16 has mounted thereon the azimuth motor and gear train 18 and i8 provided with a pivot 20 for supporting an R.F. section , A!~

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6c 72519-16 26 of a radar receiver/transmitter. The R.F. section 26 pivots in elevation on elevation pivot 24 about an axis x-x so as to permit scanning of the receiver/trans~itter platform 28 in a vertical direction with simultaneous pivotlng in the azimuth direction about azimuth pivot 20.
Antenna 27 i8 also supported by the platform 28. While the combination of the antenna and receiver/transmitter, into one assembly eliminates the need to run waveguides from the antenna to the receiver/transmitter, diffiault vibration problems result in the antenna drive system. It may be seen that the R.F. generating and receiving components are located on the elevation glmbal of ~he plat~ornl 28. This creates an adclitional mass whlah must be energized by the drive system and, in practical applications, these components are very sensitive ~o vibration and therefore must be isolated from the vibration environment. Since it is not feasible to isoIate just the R.F. components in this design, ;~
isolation has been provided by the mounts 12 between the base and electronics 10 and the aircraft mounting interface 14. However, since the center of ~ass of the system lies at a point 30 which is not co-planar with the vibration isolators, the unit tends to oscillate about a point below the isolator mounting plane under vibration. This oscillation generates substantial accelerations in the R.F. section 26, which are then transmitted as reaction torques through the drlve systems to the respective azimuth and elevation motors.

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DDSCRIPrION OF THE PREFERRED EMBODIMENT
Referring now to Figure 3, a clutah/damper for control of angular reaction torques applied by a motor-driven mass to a drive motor includes a shaft 40 coupled to a drive motor, not shown, and a gear, which may be a spur gear 42, for applyin~
; : rotary motion to a drive gear 44 which meshes with spur gear 42.
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: 7 shaft 46 rotates about an axis y-y and has a member 48 ;~ having a slip surface 50 for frictionally engaging the drive gear 44. Opposing the member 48 is a friction plate 52 slideably engaged with a second surface 54~ of drive gear 44. Friction plate 52 is translatably .
: ~ slideable across a shaft 56:also rotatable about axis y-y~ Friction plate:52 is keyed to shaft 56 to permit sliding along the axis y-y while maintaining the same angular velocity as the output shaPt 46. A sprlng 58 is compressed by locknut 60 to apply a predetermined force to friction plate 52 thereby engaging the drive gear 44 with the diskoidal member 48. Thus, the spur gear 42 : :
; ~ engaged:with drive gear 50 will also d~ive shaft 46. A:
third gear 62 on vutput shaft 46 engages the driven load 15 mass. When the load mass, not show~, is sub~ect to oscillatory vibration and exhibits a reaction torque in ;~ excess of a predetermined value determined by the '~ compressive force applied by locknut 60, shaft 46 will rotate with respect to gear 44. The reactive energy : ~ ~ 20~ transfe~rred to shaft 46 will be dissipated AS frictional : energy:at friction surfaces 50 and 54. ~ ~;
~ Since, when the reaction torque value exceeds the .~ 23 clutch setting, shaft 46 will rotate wi~h respect to ' : ~
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gear 44, there will be an angular displacement between the relative positlons of shaft 42, coupled to the drive motor, and gear 62, coupled to the load. Since accurate pointing of the radar antenna requires maintaining precise alignment of the input drive and - output load, it is desirable to interpose a feedback loop by pro-viding a control slgnal that is responsive to the angular position of the load. The control signal may be generated by any of the well known sensors, such as a tachometer, optical disk, or similar devices which are well known by one skilled in the art. This positional signal is then applied to energize an amplifier coupled to the drive motor in a closed servo loop as shown in Figure 2, so as to urge the drive motor and the load inko angular a:lignment.
It will be seen that the slipping action oE the clutch limits the level of back drive torque to the drive motor to a level that it is capable of driving and absorbs or damps the energy of the back drive torque above that level. Because the vibration induced loads will act in an essentially sinusoidal fashion, the clutch damper will slip first clockwise and then counterclockwise approximately maintaining the relative position of the driven mass.
The feedback circuit then maintains the precise relative positions.
In this way, the clutch/damper allows the use of a smaller motor to drive a given mass, thereby reducing the cost and 9~ :

: complexity of the drive system as well as the size.
Further embod1ments, shown in Figures 4 and 5, offer the advantage of incorporating resilient elements , which urge the driven mass back to its original anguLar location when the reaction torque subsideg, thereby ~ reducing or eliminating the need for position feedback.
:~ ~ Referring now to Figure 4, in which like reference numbers refer to like elements in Figure 3, the drive gear 44 i8 sandwiched between elastomeric bodies 70 and 72. Elastomerlc bodies 70 and 72 are adhe~ively a~ixed to opposite face~ of gear 44. In a like manner, the ; : opposing faces of elastomeric bodies 70 and 72 are adheslvely afflxed to the proximal faces of pl~ate S2 and~:
output member 48. It may be seen that~drive gear 44 is free to:rotate on shaft 56, while plate 52 is free to ,: :
translate along axis y-y but constrained from rotary motion re1ative to shaft 56 by keyway 64. When gear 62 is subjected to a backdrive torque from the load mass, ear 62 and:shaft 46 rotate with respect to gear 44 : 20 However, du:e to the torsional compliance of th~e elastomeric bodies 70 and 72, a portion of the:reactive : : energy is;absorbed in:deforming the elastomeric 23 material. When the reaction torque subsides, bodies 70 , ~ ~
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~ 3L29~9 and 72 urge gear 44 and shaft 46 back into alignment, so that gears 42 and 62 are angularly aligned without the requirement for posi-tional feedback.
- In a third preferred embodiment, shown in Figure 5, a drive gear 80 has a planar surface 82 engaged for rotation with member 48 of output shaft 46. An opposing face 84 of drive gear 80 has an inclined surface with respect to the planar surface 82.

Face 84 extends along a contour varying axially in a spiral fashion , :
from a mlnimum depth at the circumference of gear 80 to a maximum depth at the axis of rotation thereof. A ramp disk 86 has a corresponding inclined surface 88 for engaging the surface 84 of drive gear 80. Surface 88 has a contour varying axially in a spiral fashion from a predetermined maximum depth at th~ circum-ference to a predetermined minimum depth at the axis of rotation, so that the inclined surfaces 84 and 88 are substantially coin-cident. When ramp disk 86 is rotated with respect to drive gear 80, the inclined mating surfaces will tend to drive ramp disk 86 to ~ ~ compress spring 58~against locknut 60. It may be seen, therefore,;
;~ ~ that reaction torques applied to gear 62 and shaft 46 will be expended in the rotational friction between~surfaces 84 and 88 and in compressing spring 58 while gear 80 rotates on shaft 46, dis-placing ramp disk 86. When the reaction force is dissipated, spring 50 will tend to urge disk 86 and gear 80 back into alignment.

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Therefore, as in the case of Figure 4, the need for positional feedback is minimized.
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~; Referring again to Figure 2, it will be appreciated that the present invention lncorporates a simple ' ~:
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i297~29 , mechanism, compsred to the prior art measures previously : discussed, for absorbing reactive energy from an oscillatory load mas~. The clutch/damper may be installed in a series arrangement between the drive :
~ : 5 gears and the driven mass, therefore there is no lost ~
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: ~ energy required for overdri~:ing the stepper motor and :: alternate embodiments may reduce the need for position ; feed~ck.
While the lnvention has been described in its preferred embodlments, it is to be understood that the wordR which have been used are words of description rather than limitation and that~changes may be made within the purview of the appended claims without departlng from the true scope and spirit~of the ~ 15 invention in its broader aspects.
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Claims (4)

1. Apparatus for control of angular reaction torques applied by a motor-driven mass to a drive motor, comprising:
input means coupled to said motor and adapted for rotary motion about a first axis, drive means having first and second substantially coplanar radially disposed friction faces and adapted for rotary motion about a second axis, output means adapted for rotary motion about said second axis and coupled to energize said driven mass, wherein said output means comprises an axial shaft having a plate affixed laterally thereto, said plate having a substantially planar radially disposed face, rotatably engaging said first face of said drive means, energy absorbing means for coupling said drive means to said output means, said energy absorbing means allowing free transfer to said output means of rotary energy applied to said drive means by said input means so long as a predetermined slip torque is not exceeded, and for absorbing transfer of energy stored in said driven mass to said input means when said predetermined slip torque is exceeded, and positional feedback means including a sensor coupled to said driven mass for providing a control signal representative of an angular position of said driven mass to said drive motor and motive power means responsive to said control signal for incrementally positioning said drive motor so as to restore the relative angular positions of said output means with respect to said input means when said driven mass is angularly displaced by said reactive torque, said energy absorbing means cooperating in series relationship with said feedback means and with said drive means and said output means to provide clutch means for damping excursions of said drive motor and coupling of reactive torques between said drive motor and said driven mass in excess of a predetermined value.

2. The apparatus as set forth in claim 1, further comprising:
gear reduction means for providing rotary motion from said motor means, first gear means coupled to said gear reduction means for providing further rotary motion to said motor-driven mass and having first and second coplanar friction surfaces radially disposed for free rotation with respect to an axial shaft, output shaft means engaging further gear means for driving said mass in oscillatory motion and a further planar friction surface disposed radially upon said shaft means, friction disk means for engaging one of said friction sur-faces of said first gear means, and spring means cooperating with said friction disk means and including adjusting means for compressing said spring means so that said friction disk is further urged to engage said friction surface of said output means, said adjusting means adapted for applying a predetermined compression force to said friction disk so that said output shaft is rotatably disengaged from said first gear means when said portion exhibits at least a predetermined reactive force upon said output shaft and said output shaft is rotatably engaged with said first gear means when said portion exhibits a reactive force less than said predetermined reactive force, said reactive force when exceeding said predetermined reactive force substantially absorbed by frictional dissipation within said clutch damper means.

3. Apparatus for control of angular reaction torques applied by a motor-driven mass to a drive motor, comprising:
input means coupled to said motor and adapted for rotary motion about a first axis, drive means adapted for rotary motion about a second axis, output means adapted for rotary motion about said second axis and coupled to energize said driven mass, wherein said output means comprises an axial shaft having a plate affixed laterally thereto, said plate having a substantially planar radially dis-posed face, energy absorbing means for coupling said drive means to said output means, said energy absorbing means allowing free transfer to said output means of rotary energy applied to said drive means by said input means so long as a predetermined slip torque is not exceeded and for absorbing transfer of energy stored in said driven mass to said input means when said predetermined slip torque is exceeded, said energy absorbing means further comprising resilient means for providing a substantially sinusoidal restoring torque for maintaining the relative angular positions of said output means with respect to said input means, said input means further comprising first gear means, said drive means further comprising second gear means meshed with said first gear means and having first and second radially extending substantially planar faces, said energy absorbing means comprising first and second diskoidal bodies of elastomeric material, said first body dis-posed between said planar face of said plate and said first planar face of said second gear means, further comprising backing plate means, comprising a sub-stantially rigid planar plate distally mounted on said axial shaft from said plate and said driven mass, said second body of elastomeric material disposed between said backing plate means and said second planar face of said second gear means, means for affixing said first body of elastomeric material to said planar face of said plate of said axial shaft and to said first planar face of said drive means, and means for affixing said second body of elastomeric material to said backing plate means and said second planar face of said drive means, so that said input means resiliently engages said driven mass, and said drive means is rotatably displaced with respect to said output means when subjected to a reactive torque from said driven mass, whereby said input means is substantially disengaged from said driven mass when said reaction torque exceeds a predetermined value, and said input means is substantially engaged to said drive mass when said reaction torque is less than said predetermined value, whereby said first and second bodies of elastomer material urge said output means to rotate at the same angular velocity and relative angular displacement as said drive means when said reactive torque is dissipated.

4. Apparatus for control of angular reaction torques applied by a motor-driven mass to a drive motor, comprising:
input means coupled to said motor and adapted for rotary motion about a first axis, drive means having first and second substantially coplanar radially disposed friction faces and adapted for rotary motion about a second axis, output means adapted for rotary motion about said second axis and coupled to energize said driven mass, wherein said output means comprises an axial shaft having a friction plate affixed laterally thereto, said plate having a substantially planar radially disposed face, rotatably engaging said first face of said drive means, energy absorbing means for coupling said drive means to said output means, said energy absorbing means allowing free transfer to said output means of rotary energy applied to said drive means by said input means so long as a predetermined slip torque is not exceeded, and for absorbing transfer of energy stored in said driven mass to said input means when said predetermined torque is exceeded, said input means further comprising first gear means, said drive means further comprising second gear means meshed with said first gear means and having a first substantially planar face and a second face having an inclined surface with respect to said planar face, said surface having a contour varying in spiral fashion from a predetermined minimum dimension at the circum-ference of said second gear means to a predetermined maximum dimension at said second axis, ramp disk means having a first face with an inclined surface having a contour substantially coincident with said inclined sur-face of said second gear means, the contour of said ramp disk means varying in spiral fashion from a predetermined maximum dimension at said circumference to a predetermined minimum dimension at said second axis, said ramp disk means transversely slideable upon said axial shaft and fixed for angular rotation coincident with said shaft, and spring compression means for applying a predetermined com-pressive force to said ramp disk means for urging said inclined surface of said ramp disk means in frictional contact with said inclined surface of said second gear means, so that said ramp disk is axially displaced on said axial shaft when said reactive torque exceeds a predetermined value, thereby allowing substantially free rotation of said driven mass with respect to said input means, and said ramp disk is friction-ally engaged with said second gear means when said reaction torque is less than said predetermined value, thereby tending to urge said output means to substantially identical angular velocity and displacement with respect to said drive means.