US3060360A

US3060360A - Power assist servosystem

Info

Publication number: US3060360A
Application number: US860248A
Authority: US
Inventors: Reinhold E Tomek
Original assignee: International Business Machines Corp
Current assignee: International Business Machines Corp
Priority date: 1959-12-17
Filing date: 1959-12-17
Publication date: 1962-10-23
Anticipated expiration: 1979-10-23

Description

Oct. 23, 1962 R. E. TOMEK 3,069,360

POWER ASSIST SERVOSYSTEM Filed Dec. 1'7, 1959 2 Sheets-Sheet 1 INVENTOR Reinhold E. Tome/r m, Kim, 1% M [w ATTORNEYS Unite States This invention relates to improvements in follow-up devices or automatic control systems of the torqueless and frictionless type. More particularly, this invention relates to a control system utilized as a shaft coupling for positioning an output member in response to the position of an input member without using any of the torque of the input member, the control system characterized by the absence of any false stable null position.

In many fields of present day endeavor it is necessary to follow-up the position of an input member because the input member has very little torque applied to it to directly drive an output member. For example, in airborne and other data-handling systems, emphasis is being placed on source digitizing, i.e., converting a transducer output directly to a digital number by means of a digital converter. Since some types of transducers inherently possess very little output torque, special considerations must be made for coupling the transducer to a digital converter. That is, with practically no input torque a coupling must be devised which will provide output shaft positioning and suitable output torque.

One solution to this problem is an automatic follow-up system used as a coupling. Some of these systems, using optical means, can operate to follow the movement of an input rotary member with no torque being taken from the input member.

Various systems are known in the prior art wherein light-sensing photocells are utilized in a follow-up system. However, one of the difiiculties of the prior known systerns is the fact that they possess a stable false null. in other words, at a position 180 from the true null position the device will stabilize at a false null. This of course will produce a false output causing the follow-up device to stabilize the output position diametrically opposite the input position. Accordingly, it is the principal object of this invention to provide a torqueless coupling device for causing an output member to follow an input member by means of a follow-up system which is responsive to a radiation source and which will possess no stable false nulls.

It is an additional object of thi invention to provide a coupling for following the movement of an input member when the input member possesses little torque and none of this torque is utilized in the follow-up system, the coupling also being brushless and extremely compact.

These objects are accomplished in a torqueless coupling having no stable false nulls, by providing the coupling with a radiation source and a pair of oppositely monitored radiation-responsive devices connected in circuit to a reversible electric motor which positions an output member. An input member drives a pair of partial radiation blocking disks for metering the radiation from the radiation source to the radiation-sensitive devices and the output member also drives a pair of partial radiation blocking members such that movement of the input member will cause a greater radiation reception at one or the other of the oppositely monitored radiation-responsive devices in accordance with directional movement of the input member, and the motor in responding to the radiation reception will drive the output member toward the stable null position.

Other objects and advantages of the invention will be pointed out in the following description and claims and v illustrated in the accompanying drawings which disclose,

"ice

by way of example, the principle of the invention and the best mode which has been contemplated of applying that principle.

In the drawings:

FIG. 1 is an exploded view of the mechanical components of the torqueless coupling of this invention;

FIG. 2 is a schematic illustration of the coupling of this invention in a balanced or null position;

FIG. 3 i a schematic illustration of the coupling of this invention after the input shaft starts to rotate clockwise;

FIG. 4- is a schematic illustration of the coupling of this invention after the input shaft starts to rotate counterclockwise;

FIG. 5 is a schematic illustration of the coupling of this invention showing the position at a false null and how such position is unstable.

In general, the torqueless coupling of this invention contemplates at least one radiation source such as balanced light for directing light equally toward a pair of oppositely mounted photocells or other radiation-responsive devices. An input shaft and an output shaft are axially aligned and the input shaft drives a pair of partially opaque sectored disks attached thereto. One of these disks is on one side of the central light source and the other disk is on the other side. Each disk serve to partially block the light radiated toward each of the photocells. The output member likewise drives a pair of partially opaque sectored disks and each one of these disks is similarly positioned on opposite sides of the light source to partially block the response of the photocells. The arrangement is such that by rotating the input shaft in one direction, one of the photocells produces an output greater than the other and this net output is fed to a DC. amplifier and then to a reversible servomotor to rotate the output shaft and thereby move the pair of sectored disks connected thereto to a position angularly coinciding with the input shaft position to again balance the response on the photocells. At a stable null position a very small amount of light reaches each photocell and the small voltage generated is the same for each photocell, thus the system is balanced. When the input is rotated from its stable null position, full light will reach each of the photocells and the system will be momentarily balanced at a false null position. However, by moving the input or output shaft only slightly from this false null one of the photocells receives more light than the other. This net output from the oppositely monitored photocells will cause the reversible motor to drive the output shaft in a direction opposite to the input shaft rotation causing the balanced stable null position to be again obtained.

Referring now to the drawings, FIG. 1 is an exploded perspective view of the torquelesscoupling of this inven tion. As shown in FIG. 1, a balanced light source 10, which may consist of a plurality of electric lamps 12 and a pair of frosted glass covers 14 and 16 within a cylindrical upport housing 18, is provided. The balanced light source 10 is adapted to provide approximately the same amount of'light from each side thereof. A pair of split covers 20 and 22 are attached to the light source housing 18. The attachment may be by

suitable screws

24 and 26 or the like.

A radiation-responsive device such as a

voltage generating photocell

28 and 30 is positioned within each split cover. An input shaft 32 is journalled in a bearing 34 in cover 20, and a pair of partially opaque sectored

disks

36 and 38 are rigidly secured to the shaft 32. Disk 36 is positioned between balanced light source 10 and photocell 28, while disk 38 is positioned between balanced light source 10 and photocell 30. Disk 36 has a quarter sector 37 which is transparent and a three quarter sector 39 3 which is opaque. Disk 38 is half transparent at 35 and half opaque at 41.

An output shaft 42 is journalled in a bearing 71 in cover 22, and is rigidly connected to a disk 44. The disk has an opaque area 43 and a transparent area 45 similar to disk 36. A transparent coupler member 46 is rotatably journalled on input shaft 32 by suitable bearings 48 and has a collar extension 50 extending from one side thereof through the light source housing 18 and journalled therein by bearing 70. A pair of lugs 52 extend longitudinally of the axis of the coupler to co-operate with notches 54 in disk 44 to establish a driving connection between the coupler 46 and the disk 44. The collar 50 of coupler 46 is likewise rigidly connected to a disk 56 by means of a key 63. Disk 56 is also half opaque 55 and half transparent 57 similar to disk 38. it can be seen with this arrangement that the input shaft 32 drives

disks

36 and 38 directly to partially block the light from light source directed toward both

photocells

28 and 30. In a similar manner output shaft 42 directly drives

disks

44 and 56 to also partially block the light transmitted from light source 10 to both photocells 28 and 3t Thus, the disks are, in effect, light shutters. By the arrangement of one disk of each connected set being on opposite sides of the light source the angular movements of the disks control a bi-directional independent response, e.g., if disk 36 is moved to allow more light to photocell 28 disk 38 is moved in a direction which will not affect the response of photocell 30.

As shown in FIGS. 1 and 2, the opaque and transparent areas of the sectors are arranged such that at the true null position, shown in FIG. 2, the small amount of light transmitted to each photocell balances the system. The photocells are oppositely monitored or oppositely connected in the circuit, for example, photocell 28 may produce a positive output voltage to a DC. amplifier 60 while photocell 30 may produce a negative voltage to the amplifier. A reversible servomotor 70 is driven by the output of DC. amplifier 60 and motor 70' is mechanically coupled to the output shaft 42 by a suitable connection 72. As can be seen from FIG. 2, at the true stable null position the

sectors

56 and 36 meter the radiation from light source 10 to photocell 28 and similarly

sectors

38 and 44 meter the radiation from light source 10 to photocell 30. With equal reception of a small amount of light the net output of these cells will be zero, i.e., the response will be balanced, and the output shaft will then be positioned according to the angular position of the input shaft.

FIG. 3 illustrates the condition of the device when a clockwise movement is applied to the input shaft. When this happens, the sectored

disks

36 and 38 rotate clockwise and the transparent area 37 of disk 36 combined with the transparent area 57 of disk 56 allows increased radiation from light source 10 to energize photocell 28 while the light to photocell 30 remains blocked producing a net positive voltage to the DC. amplifier 60 causing the motor 70 through its mechanical connection 72 to rotate the output 42 clockwise. Rotation of the output shaft clockwise drives

disks

44 and 56 clockwise, the opaque area 55 of disk 56 gradually cutting off the light transmitted from light source 10 to photocell 28 until a balanced stable null condition is again obtained. At this position the output shaft 42 has moved clockwise to an angular position coincident with the angular position of the input shaft 32.

FIGURE 4 illustrates the device when a counterclockwise movement has been applied to the input shaft 32. This counterclockwise movement causes the transparent area 35 of disk 38 to allow increased light to pass from light source 10 through transparent area 45 of disk 44 onto photocell 30, thus producing a net negative voltage to DC. amplifier 60, causing reversible servomotor 70 to rotate the output shaft 42 through connection 72 in a counterclockwise direction. This counterclockwise movement causes the opaque area 43 of sector disk 44 to move into the path of light falling on photocell 3t) and gradually cut it off, approaching a balanced stable null condition. Should the inertia of the system carry the output shaft beyond this point, the light response of the positively monitored photocell 28 will increase, driving the output shaft in a clockwise direction until the stable null is reached.

FIGURE 5 illustrates the input shaft 32 at a false unstable null position 1 opposite the stable null position. At the false null position, it can be seen that maximum light is transmitted from light source 10 to both

photocells

28 and 30 and the net output to the amplifier 60* is zero. However, the quarter sector transparent area of

disks

36 and 44 does not allow the light to saturate the photocells 28 and 30'. That is, the exposure of both photocells to maximum light will still allow reductions in the light shutter openings to effect the voltage output of the photocell. If maximum light were to saturate the photocells the unstable null condition could exist for small rotational deviations from this condition since no net output voltage variation would exist. A saturation condition can be prevented by changing maximum allowable shutter opening or by a diminishing light source, preferably the latter.

With the coupling at a false null position wherein maximum light will not saturate the photocells, slight movement of the input shaft 32 in either a clockwise or counterclockwise direction will diminish the output of one or the other of the photocells producing a net output to amplifier 60. For example, from the unstable false null position any movement of the input shaft 32 in a clockwise direction will cause the light transmission from source 10 to the photocell 28 to decrease, while maximum light is still reaching photocell 30. This provides a net negative output fromthe combined photocells to the DC. amplifier 60, driving the output shaft 42 from the motor 70 in a counterclockwise direction which in turn further increases the net negative output, causing shaft 42 to continue to be driven with increased rapidity in a counterclockwise direction for until the balanced stable null is reached. In other words, when moving from an unstable false null to a stable null position one photocell continues to see maximum light through a transparent quarter sector and the light to the other photocell is diminishing. Therefore the motor 70 will drive the output shaft 42 with increased rapidity toward the stable null position.

Applicants invention thus essentially includes the oppositely monitored photocells for causing a reversible motor to rotate in opposite directions to position an output shaft in combination with partially opaque and partially transparent inline rotatable disks connected in pairs to the input and output shafts. By having one disk of each connected pair on each side of the light source as control shutters for oppositely monitored photocells, each disk pair effectively rotates in opposite angular photocell response directions such that one disk of each connected pair is affecting light reception at one photocell more than at the other photocell. This situation is accomplished only by having one disk of each pair between the light source and each oppositely monitored photocell and having a pair of disks connected to both the output and input shafts.

As can be seen from the foregoing, applicant has disclosed a compact torqueless coupling possessing no stable false nulls and utilizing in-line partially opaque sector disks. It should be pointed out that the opaque and transparent areas of the disks are arbitrary and other configurations of opaque and transparent areas could be utilized to produce the same results. Also, although an electric light and current-generating photocells have been utilized as the source and sensing means, other sources and sensing means known in the art are contemplated. For example, any source of radiation and any pair of oppositely monitored radiation-responsive devices with means for blocking the radiation similar to the disks illustrated in the preferred embodiment could be utilized.

While there have been shown and described and pointed out fundamental novel features of the invention as applied to the preferred embodiment it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is:

l. A torqueless coupling comprising; at least one radiation source, a pair of radiation responsive devices, a reversible motor, means connecting the radiation responsive devices to the reversible motor such that when one of the radiation responsive devices receives more radiation than the other one the motor will rotate in one direction and when the other radiation responsive device receives more radiation than the first one the motor will rotate in the opposite direction, a rotary input shaft, a separate rotary output shaft, a driving connection between the output shaft and the reversible motor, a pair of members partially opaque and partially transparent to transmitted radiation connected to the input shaft and another pair of similar members connected to the output shaft, one of each pair of the members being positioned between the radiation source and one radiation responsive device to partially block the response of each radiation responsive device from the radiation source such that the movement of the input shaft in either angular direction will thereby vary the response of the radiation responsive device due to movement of the opaque andtransparent areas on the partially opaque and partially transparent members and this variation in response will cause the reversible motor to drive the output shaft in a direction to cause the response of the radiation responsive devices to balance at a stable null position when the output shaft is angularly referenced to the input shaft.

2. A torqueless follow-up control system comprising; a light source, a pair of oppositely monitored light sensitive devices, a pair of separate rotary systems, each of said rotary systems connected to a pair of partially opaque, partially transparent members, a member of each rotary system being interposed between said light source and one of said light sensitive devices, whereby a pair of partially opaque, partially transparent members, one connected to each separate rotary system will be interposed between said light source and each light sensitive device, the opaque and transparent areas on each mem ber being arranged to allow only a small amount of light from the light source to reach said light sensitive devices when the separate rotary systems are angularly aligned, and when the separate rotary systems are angularly offset allowing light to reach separate light sensitive devices depending upon the direction of angular offset, and a reversible motor operatively connected to one of the separate rotary systems for rotating the system and bring it back to a condition of angular alignment, the motor being controlled by the response of the light sensitive devices.

3. A torqueless coupling connecting an input shaft to an output shaft to cause said output shaft to move the same amount and in the same direction as the input shaft, said coupling comprising; a reversible electric motor connected to drive the output shaft, a source of light, a pair of oppositely monitored photocells, electrical connections between said photocells and motor for driving said motor in a direction depending upon the output of the photocells, a pair of disks between the light source and each photocell, one of said disks of each pair connected to the input shaft and the other being connected to the output shaft, means defining opaque and transparent areas on said disks such that when the input shaft position and output shaft correspond at a stable null position each photocell has an equal response and when the input shaft is moved in either direction the movement of the connected disks allows the net output of said photocells to increase to drive the motor selectively in either direction, the parameters of the light source and the opaque and transparent areas on the disks being such that at maximum light reception the photocells will not be saturated, the false null position diametrically opposite the stable null position being unstable due to any slight movement of the input or output shaft producing an unbalance in the reception of the photocells producing a net output and causing the motor to drive the output shaft back to the balance stable null position.

4. A torqueless coupling as defined in claim 3 wherein the source of light, the photocells, the input and output shafts, and the disks carried by the input and output shafts are axially aligned.

5. A torqueless coupling as defined in claim 4 wherein the axially aligned components are enclosed in a. compact cover member totally enclosing said components with the exception of extensions of the input and output shafts, and bearings being carried by said cover member for journalling the input and output shafts.

6. A torqueless coupling as defined in claim 5 wherein the pair of disks connected to said output shaft are connected together by means of a transparent mechanical coupling member, the coupling member being rotatable on the input shaft and having axial extensions rigidly connected to each of the disks on the output member.

7. A torqueless coupling as defined in claim 5 wherein the opaque and transparent areas on the disks are sectors of a circle, one disk of each pair being a half sector opaque and a half sector transparent while the other disk of each connected pair being one quarter transparent and three quarters opaque in sectors.

8. A torqueless coupling comprising; an input shaft and an axially aligned separate output shaft, a split housing, each half of said split housing containing a bearing for journalling each of said shafts, a balanced light source positioned substantially in the center of the housing to direct light in opposite directions of equal intensity, a pair of oppositely monitored photocells positioned in each end of said split housing on opposite sides of said balanced light source, a reversible electric motor operatively connected to drive the output shaft, electrical connections between said oppositely monitored photocells and said motor for driving said motor in the direction depending upon the response of the photocells and the net output therefrom, a pair of disks rigidly connected to said input shaft, one of said disks being on each side of said balanced light source, a disk rigidly connected to said output shaft and positioned thereon between the balanced light source and the photocells, a coupler unit journalled in a bearing in said balanced light source housing and rigidly connected to saiddisk on the output shaft, another disk rigidly connected to said coupler and positioned between said balanced source and the other photocell, means defining opaque and transparent areas on said disks such that when the input shaft position and output shaft position correspond a balanced stable null position is reached with each photocell receiving equal response from the light source, and when the input shaft is moved in either direction relative to the output disk, the connected disks allow the response of the photocells to the transmitted radiation from the balanced light source to vary in a direction which will cause the reversible motor to drive the output shaft back to the stable balanced null position, the parameters of the light source and the opaque and transparent areas on the disks being such that at maximum light reception the photocells will not be saturated, whereby a false null position diametrically opposite the stable null position will be unstable due to any slight movement of the input or output shaft causing the motor to drive the output shaft with increased rapidity back to the balanced stable null.

9. A power assist servosystem comprising; at least one radiation source, a pair of radiation responsive devices, a drive means having a reversible output and the drive means being operatively connected to the radiation responsive devices such that when one of the radiation responsive devices receives more radiation than the other one the reversible output of the drive means will move in one direction and when the other radiation responsive device receives more radiation than the first one the reversible output of the drive means Will move in the opposite direction, a rotary input system, a separate rotary output system, an operative connection between the out put system and the reversible output of the drive means, a pair of members partially opaque and'partially transparent to transmitted radiation connected to the input system and another pair of similar members connected to the output system, one of each pair of the members radiation responsive device to partially block the response of each radiation responsive device from the radiation source such that the movement of the input system in either angular direction will thereby vary the response of the radiation responsive device due to movement of the opaque and transparent areas of the partially opaque and partially transparent members and this variation in response will cause the reversible output of the drive means to drive the output system in a direction to cause the response of the radiation responsive devices to balance at a stable null position when the output system is angularly referenced to the input system.

References Cited in the file of this patent UNITED STATES PATENTS