JPS59166753A - Friction driving mechanism - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a drive mechanism, and more particularly to a friction drive mechanism.

Drive mechanisms of this type to which the present invention relates, which are applied at high speeds and with high precision, requiring, for example, start and stop stepping and reversing, are well known in the art. A typical application of this is a positioning and measuring system that controls servo motors to automatically position a tool and a workpiece relative to each other according to a desired operating program. A method for measuring positioning using an interferometric laser to provide a position feedback signal is disclosed in commonly assigned U.S. Pat. No. 3,884.
．． No. 580, No. 1; described and explained.

Such applications require output drive operation that accurately responds to input command signals without outputting error signals from the drive mechanism. Although the present invention is useful in anything requiring a drive mechanism, the drive mechanism is particularly disclosed in a high-resolution plotting system in which a tool is configured to plot graphical information of a workpiece. This is the optical head used.

Mechanically rigidly connected drive mechanisms using gears, pole lead screws, etc. are required to provide the necessary fast response times to provide the speed and accuracy required in high speed, high precision servo system applications. Invented on purpose. However, due to the inflexibility of the drive mechanism and low braking,
These servo systems are susceptible to device resonances that occur within the excitation frequency of the gear teeth, for example. This resonance in turn contaminates the feedback control information creating instability and the system moves erratically to damp the feedback signal to zero. The roots of this instability are well known to those skilled in the art, and although elaborate solutions have been proposed to minimize their effects, it is best to eliminate these root problems. It is.

Also, as the drive mechanism moves a load back and forth from one position to the next, gears or other mesh drive mechanisms are subject to backlash. Backlash directly introduces errors into the system because the position of the output gear relative to the input drive gear is not consistent at all times and load positions. If the output gear is driven in one direction and the input gear is in the opposite direction, the input gear must be rotated a small amount before the input gear teeth contact the opposite side of the output gear teeth. Must be. Furthermore, since torque is applied to the teeth of the input gear and the output gear, they act like a spring, causing backlash play at a constant drive speed.

Therefore, backlash is the main source of excitation that causes resonance in the device. The way to minimize and eliminate backlash is to create complete gears or use spring-loaded split gears or pre-loaded pole lead screws, so that the drive element follows the forward and reverse directions without any lag. Hold pressure on both sides.

Additionally, gear rattle generally creates an irritating and unwanted noise. Lubrication is required at periodic intervals to minimize the noise generated and extend the service life of the gear mechanism.

It is therefore a general object of the present invention to provide a friction drive mechanism in which the sources of resonance are minimized or eliminated and the dynamic operation of both the drive mechanism and the driven device is improved. be.

Another object of the present invention is to provide a friction drive mechanism that is particularly applicable at high speed and with high precision.

Yet another object of the invention is to provide a friction drive mechanism with improved reliability and minimized operational noise.

Other objects and advantages of the invention will be apparent from the drawings and the following description.

The present invention relates to a friction drive mechanism having a driven wheel connected to a drive motor and a driven wheel connected to an output shaft, the driving wheel and the driven wheel moving relative to each other. For this purpose, it is attached tangentially to the center of the wheel and a contact point located along a straight line extending through this center. A pressure wheel is mounted in contact engagement with one of the driving wheel and the driven wheel to apply a pressing force between the driving wheel and the driven wheel at the point of contact;
It is placed on one side of both wheels, facing from the other of the wheels. The pressing force generating means adjusts the amount of pressing force transmitted by the pressing wheel to one of the driving wheel and the driven wheel.

The present invention further relates to a closed loop servo system having a servo motor and a friction drive mechanism for moving an output element between multiple positions according to an input position command signal. The sensing means is arranged to produce a feedback signal appearing on the output element by the friction drive mechanism, and the summing means receives the feedback signal producing a position error signal for driving the servomotor. A high precision servo system is described to help familiarize the reader with this type of system in which the present invention is used.

FIG. 1 illustrates a photoplotter, designated by the numeral 10, which has a friction drive mechanism used in the present invention, designated by 21.29. The photoplotter automatically positions the optical photohead 11 and the film plate F relative to each other according to the desired work program and exposes the film with lines and symbols placed with an accuracy of about 0.005 cm (0.002 inches). However, the invention is not limited to photoplotter applications, but can be used in other devices requiring a drive mechanism.

The photoplotter shown in FIG. 1 has a stationary support frame 12 with legs 13, a support pedestal 14 and an overlying bridge 15. The photoplotter shown in FIG. This bridge 15 is rigidly connected to the frame 12 and rests at a raised height on the middle part of the support base 14.

The work table 16 has a work surface on which the film plate F is held stationary. The work table is mounted on a pillow block which is rigidly connected to the underside of the work table, and which has a pair of cylindrical passages 17 mounted on a support base 14.
．． 18 in the X coordinate direction.

The movement of the work table 16 in the X coordinate direction is controlled by the X drive motor 1.
9, a single lead screw 20 is rotated by the friction drive mechanism 21 of the present invention, and a pole nut (not shown) is connected to the underside of the central portion of the work table. The drive mechanism 21 is encased in a frame 40 attached to the stationary support frame 12.

Drive motor 19 is connected to plot controller 22 through command signal cable 23. The controller 22 derives plotting commands from the program tape 24 and transmits them to the drive motor 9 for positioning the worktable 16 and film F at various positions along the X-coordinate axis during plotting operations.

The optical photohead 11 is supported and moved over the film plate Ftil- by means of a tool carriage 25. The photohead has an optical axis 26 extending substantially perpendicular to the photosensitive surface of the film F and the X, Y coordinate axes, and the photohead exposes the film surface by emitting a beam of light along the optical axis. Exposure occurs as the film plate and photohead move relative to each other, so that a continuous line is exposed.

Still referring to FIG. 1, a tool carriage 25 is mounted on the bridge 15 for movement along the bridge 15 in the indicated y-coordinate direction by means of an Rotated by the friction drive mechanism 29 of the present invention, the pole nut 30 is mounted on the tool carriage. Command signals derived from the program tape 24 are also supplied by the controller 22 to the X drive motor 27 to position the photohead laterally along the bridge 15 with respect to the film plate F. It will be appreciated that the combined movement of the film plate 1-F and the photohead by the X and X drive motors 19.27 allows the photohead to expose any area of the photosensitive surface of the film F.

The operation of the photo head 11 and work table 16 is based on the film F.
In order to accurately expose the above plot, it is measured by means of a laser interferometer system.

This interferometer means is simply a dual axis system that measures motion in both the X and Y coordinates.

A helium-neon laser 31 is mounted on a support 14 to generate a laser beam, and the laser beam is connected to a laser X-axis tip detector and a The laser's y-fine photodetector is used to measure along the plane coordinate axis. The generated laser beam is transmitted to a beam splinter (not shown) mounted on the bridge 15. This beam splitter directs a portion of the beam to an X-axis interference needle 32 mounted on the tool carriage and another portion of the beam to a Y-axis interference needle 33 mounted on the bridge 15. The X-axis interference needle 32 is operated by a long mirror 34 mounted on the work table 16 at one end and has a measuring axis 35 extending between the interferometer 32 and the long mirror 34 in the X direction, labeled.

The reflective surface of the mirror 34 is perpendicular to the measuring axis 35 and extends in the {circle around (2)} direction, so that the measuring axis traverses the reflective surface at each position of the tool carriage 25 along the lead screw 28.

The Y-axis interferometer 33 is connected to this interferometer and the tool carriage 25.
It has a measurement axis extending between retroreflectors 37 mounted above. This tool carriage 25 is parallel to the axis 36
Because of the movement in the coordinate direction, retroreflector 37 is not elongated and is placed in intersecting relationship with axis 36 at each position of tool carriage 25 and work table 16.

The term ``measurement axis °°'' refers to the axis along which the interferometer emits a coherent beam of light to a separate reflector in order to measure the relative motion between the interferometer and the reflector. This axis is actually a midpoint line between two or more parallel beams of light, and since the beam is reflected at a point between the interferometer and the reflector, the measurement axis is The term "transverse" refers to a geometric condition in which a line, or an extension of a line, passes through a particular point, line, or plane.

Now, returning to FIGS. 2 to 4, the X-axis friction drive mechanism housed in the frame 40 as shown in FIG.
Illustrated by example. The Y-axis friction drive mechanism 29 is housed in a frame 57 attached to the bridge 15.
It will be appreciated that it is similar in appearance and operation to the X-axis friction drive mechanism.

Therefore, explanation and description of the Y@friction drive mechanism will be omitted.

The X drive motor 19 is mounted to a suspended support frame 41 as best illustrated in FIGS. 2 and 4. This suspended frame is connected to one end of a bending hinge 44. The term "one-turn hinge" is used herein to refer to an integral resilient hinge formed by directly weakening the sides of the member by forming grooves or indentations. A hinge made in this way pivots the nail material onto the pivot l, allowing it to act with sufficient precision as a support. The opposite end of the bending hinge is connected to a stem 45 that extends through the frame 40. This stem 45 is held in position by a retaining nut or collar 46. The frame 41 can rotate about the centerline 47 of the stem 45 and is easily aligned within the friction drive mechanism 21 as described in detail below.

The rotational movement of the bending hinge 44 causes the suspended frame 4
Limit the horizontal movement of the hanging type 1.

The friction drive mechanism 21 includes a friction drive wheel 4 mounted on a drive shaft 42 of the motor 19 shown in phantom lines in FIG.
3 and a friction driven wheel 38 connected to the output shaft or lead screw 20. Lead screw 20 is mounted to support frame 12 through ball bearings 39 in a conventional manner.

Such an arrangement allows the lead screw 20 to rotate, but prevents lateral movement on the lead screw 20.

The driving wheel 43 is supported by the motor 19 in tangential relation to one side of the driven wheel 38 and is moved toward and away from the driven wheel by lateral movement of the suspended frame 41.

Push wheel 49 is shown rotatably mounted to yoke 50 on the side of driving wheel 43 opposite driven wheel 38. The yoke 50 is rigidly connected to the upper end of the movable arm 5B with a hinge 51 bent near the opposite lower end. The hinged end of this arm is secured to the frame 40 by screws 52 to axially align the suppression and drive wheels to maximize surface contact area and uniform wear. The rotational movement of the bending hinge 51 is performed by the arm 58, the yoke 50, and the driving wheel 4.
3 and restricts the lateral movement of the hanging mold of the pressing wheel 49 toward and away from the press wheel 49.

As best shown in FIGS. 3 and 4, the suppression wheel 4
The shaft end of 9 has a flange with a rim 56 which provides a contact surface for the driven wheel 43 at a location on either side of the contact surface that contacts the driven wheel 38 . Both wheels are constructed from stainless steel with a hardness of 50-60 Rockwell C with minimal surface wear.
A favorable friction surface is obtained for the transmission of drive torque between the driving wheel and the driven wheel.

The spring-pressing plunger 54 attached to the frame 40 is
A force is applied to the movable arm 58 in a direction in which it contacts the circumferential surface of the wheel 43 that drives the suppression wheel 49 . The resilient support of the motor 19 by the suspended frame 41 brings the circumference of the driven wheel 38 into sequential contact with the driven wheel 43 for frictional torque transmission. Pressure adjustment screw 55 provides means for increasing or decreasing the pressure on spring-loaded plunger 54 to adjust the force applied between arm 58 and both wheels 38 and 43. Increasing the force on arm 58 is achieved by using two wheels 38 and 4.
At the point of contact between 3.

The purpose is to transmit a large force to the suppression wheel 49. The arrangement of the suppression wheel and spring-loaded plunger in the same plane of the driving and driven wheels also eliminates bending stresses on the motor shaft 42 of the motor 19.

The driving wheel 43 transmits the maximum torque to the driven wheel 38 when the axes of both wheels are aligned perfectly parallel, since the maximum friction occurs when the area of surface contact between both wheels is the largest. do.

This arrangement aligns the centerline 4 of the stem 45 so that the axis of the driving wheel is aligned parallel to the axis of the driven wheel.
This is accomplished by rotating the suspended frame 41 around 7. This arrangement is held by a set screw 48 of a collar 46 that tightens against the stem 45 and is secured by a screw 53.
It is held unchanged by fixing the stem to a frame 40 that has a handle. Some slippage occurs between the driven wheel and the driven wheel, but the amount is minute;
It is not critical for positioning feedback system applications.

In summary, friction drive mechanisms have been described that avoid traditional problems associated with excitation of gears in gear drive mechanisms used in high speed, high precision servo system applications. Resonances and noise sources are minimized or eliminated, and dynamic operation of both the driving wheel and the driven wheel apparatus is improved.

The foregoing description describes the preferred embodiments of the invention, and numerous substitutions and modifications may be made without departing from the spirit of the invention. For example, the suppression wheel 49 is arranged to direct the driven movable support wheel 38 towards and away from the fixed driving wheel 43. Similarly, the hinging motion of the suspended hinges 44,51 is performed with a pin-mounted pivot hinge. Accordingly, the invention has been described merely in an illustrative rather than limiting manner.

[Brief explanation of drawings]

1 is a perspective view of a photoplotter using the mechanism of the present invention, FIG. 2 is a front view of the preferred configuration of such a mechanism using the photoplotter, and FIG. 3 is a perspective view of the line 3-- 3 is a top view of the mechanism for producing the cross-sectional view of FIG. 3, and FIG. 4 is an elevational view of the mechanism for producing the cross-sectional view along line 4--4 of FIG. 10...Photoplotter, 11...Photohead, 12
...Support frame, 13...Legs, 14...Support stand, 15...Bridge, 16...Work table, 1
7.1'8... Cylindrical passage, 20... Lead screw, 21... Friction drive mechanism, 22... Plot controller, 23... Cable, 24... Program tape, 25...・Tool carriage, 26...optical axis,
27...Y drive motor, 28...Lead screw, 29
...Friction drive mechanism, 31...Helium neon laser-132...X-axis interference needle, 33...Y-axis interference needle, 3
4...Mirror. 35... Measurement axis, 36... Axis, 37... Retroreflector, 38... Driven wheel, 40... Frame, 41... Support frame, 42... Motor shaft, 43... Driving wheel, 44... Suspension hinge, 45... Stem, 46... Collar, 47... Center line, 49... Pressing wheel, 50... Yoke, 5
DESCRIPTION OF SYMBOLS 1... Suspension hinge, 52... Screw, 54... Spring pressing plunger, 56... Rim, 58... Movable arm. Inssu + V-kan 1-・〃nlζ21

Claims (6)

[Claims] (1) an input shaft and an output shaft; a driven wheel connected to the output shaft for transmitting rotational drive of the output shaft; and a driven wheel for transmitting rotational drive from the input shaft; a driving wheel connected to the driving wheel, wherein the driving wheel and the driven wheel are in a tangential relationship with the center of both wheels and a contact point provided along a straight line extending through the centers of both wheels. In a friction drive mechanism of a drive train mounted in a suppression wheel; a first support holding said pressure wheel for at least limited movement toward and away from one of the driving and driven wheels; and a driving wheel at said point of contact; and the driving wheel and the driving wheel for at least limited movement toward and away from the other of the driving wheel and the driven wheel so as to apply pressure between the driving wheel and the pressing wheel. a second support holding one of the wheels to be driven, and pressing the pressure wheel towards the one of the driving wheel and the driven wheel, thereby at the point of contact the driving wheel and the driven wheel; generates pressure between
A friction drive mechanism for a drive train, characterized in that a wheel driven by friction has a pressing force generator that transmits drive torque to the driven wheel. (2) The second support has a wheel that is driven in a stationary relationship, and a third support that holds the other of the driven wheels and rotates the other of the two wheels. A friction drive mechanism for the drive train according to scope 1. (3) The friction of the drive train according to claim 2, wherein the first support has a movable arm attached to the third support for holding the pressing wheel. Drive V & structure. (4) The friction drive mechanism according to claim 3, wherein the movable arm has a bendable hinge provided near one end of the arm. (5) The pressing wheel has a flange at each shaft end, and the flange has a rim for surface contact engagement with the one of the driving wheel and the driven wheel. The friction drive mechanism according to item 5. (6) A servo motor that moves an output element between multiple positions and moves the output element according to an input command signal, a sensor that outputs a feedback signal when the output element moves, and an error signal that generates an error signal to drive the servo motor. a summing device that receives and receives the feedback signal to perform a closed loop servo system, the system having a driven wheel connected to an output element and a driven wheel connected to the servo motor; and said driven wheels are mounted in tangential relation to each other with a contact point disposed along the center of said rainwater eel and a straight line extending through said centers of both wheels;
mounted for tangential engagement with one of the driving and driven wheels, opposite the other of the wheels, with a contact point located near a straight line extending through the center of both wheels; a suppression wheel provided on said one of both wheels, pressing said suppression wheel towards said one of said driving wheel and said driven wheel, and frictionally engaging said output element by means of said servo motor; A friction drive mechanism characterized in that it has a pressing force generator.