ARTICLE HANDLING ARRANGEMENT

Abstract: An article handling structure includes an arrangement for monitoring the orientation of the second end (58) of a link arm (50) with respect to the first end (42) of the link arm. A light beam source (45) is mounted on the first link end and is adapted to direct at least one light beam along said link arm to a predetermined position on said second end and a light beam detector (55) mounted on said second end is adapted to produce a signal representative of orientation of the second end with respect to the first end responsive to said light beam.

Description: ARTICLE HANDLING ARRANGEMENT Background of the Invention The invention relates to article handling and, more particularly, to robotic structure positioning arrangements. Automatic handling of articles in manufacturing and transporting operations generally requires monitoring the precise location of an article being manipulated. In robotic type apparatus, the control arrangements incorporate position sensors and circuitry to keep track of the current position of the article in relation to the desired article location. A robot arm may, as is well known in the art, comprise one or more links interconnected by joints and terminating in a manipulator adapted to support the article being operated upon. The motion of the arm is directed by a control device, generally computer operated, that applies signals to the joints and to the manipulator. Precise signals indicative of arm location are generated at the joints and the manipulator so that the control device may automatically adjust the robot arm motion signals in accordance with a programmed design. Techniques for measuring the positions and angles of robot arms are well known. Position monitoring is usually based on the assumption that robotic elements are rigid and not subject to deformation. The rigidity assumption is valid only when the robotic elements are sufficiently massive in relation to the article being handled. Consequently, robotic elements are generally made of stiff massive materials. The use of such materials, however, makes the design of the joints and the apparatus needed to move the joints more difficult and more expensive. If a robotic element is subjected to deformation owing to the weight and inertial properties of the handled article or the rigidity of the link, the resulting changes in element end position are not incorporated into the motion control and the required operation may not be successful. Thus, it is desirable to devise an arrangement that permits robot structures which are limited in mass, size, or rigidity to handle other than small and light articles. U. S. Patent 4,119,212 discloses a system adapted to monitor the location of a robot hand that takes into account deformation of robot arm elements. This technique utilizes a pair of linking elements of known lengths that are interconnected by a free floating pivotal joint. The linking elements are pivotally coupled to different robot arm elements and sensing devices are incorporated at the free-floating pivotal joint and at the pivotal coupling points on the arm elements. The sensing devices measure the angle between the linking elements and the attitude of the linking elements so that the position of the robot arm article holding end may be calculated independent of any deformation. This prior art system, however, is subject to errors in position determination due to mechanical inaccuracies in the sensing devices especially where the angular movement is small. Further, the free-floating pivotally joined linking elements as depicted in U. S. Patent 4,119,212 are adapted to single plane operation. Deformations, however, may occur in any direction as a result of article mass, or inertial or other effects and may be the result of external torsional forces or lack of link element rigidity. It is an object of the invention to provide an improved article handling arrangement that results in accurate orientation monitoring independent of the magnitude or type of deformation in the article handling structure. Brief Summary of the Invention The invention is directed to an article handling structure having a link arm with first and second ends in which the positions of the ends are monitored. A light beam source is mounted on said first link end and is adapted to direct at least one light beam along said link arm to a predetermined position on said second end. A light beam detector mounted on said second end is adapted to produce a signal representative of orientation of the second end with respect to the first end responsive to said light beam. According to one aspect of the invention, a control arrangement is responsive to the orientation representative signal to reposition said link arm to compensate for said link arm loading. According to another aspect of the invention, the light beam source directs alternate light beams along said link and the light beam detector provides a pair of signals responsive to the alternate light beams so that the orientation representative signal is indicative of torsional and bending deformation of the link arm. Brief Description of. the Drawing FIG. 1 depicts a robotic arm structure illustrative of the invention; FIG. 2 shows details of one link of the robotic arm structure of FIG. 1 in an undeformed condition; FIG. 3 shows details of the link of FIG. 2 in a deformed condition; FIG. 4 shows a schematic diagram of a light beam .source and detection circuit useful in the arrangements of FIGS. 1, 2, and 3; FIG. 5 shows another type of photodetector structure that may be used in the arrangement of FIG. 4; FIG. 6 shows a schematic diagram of another light beam source and detection circuit useful in determining torsional as well as bending deformation of a link arm structure; FIG. 7 shows waveforms illustrative of the operation of the circuit of FIG. 6; and FIG. 8 illustrates the phase sensitive detector circuit of FIGs. 4 and 6. Detailed Description FIG. 1 shows a robot arm device 10 offset at an angle froi ϋ:3 vertical orientation that is adapted to handle article 70. Arm 10 includes an articulatory joint 20 which connects stationary member 15 to hollow robotic link element 30 at end 22. End 42 of hollow link element 50 is connected to end 32 of link 30 by articulatory joint 40 and manipulator elements 65 are attached to end 58 of link 50 through manipulator joint 60. Article 70 is held in a prescribed position by manipulator elements 65. Each joint of robot arm device 10 is separately controlled by a control device 90 which may comprise one of the many computer arrangements for robotic control well known in the art. Control device 90 is adapted to coordinate the operations of joints 20, 40 and 60 and manipulator elements 65 so that the arm movement accomplishes a desired task with respect to article 70. Link elements 30 and 50 may be of the telescoping type as indicated in FIG. 1 or may be straight link elements- well known in the art. Signals representative of the current locations of the link elements and the manipulator of robot arm device 10 are required by controller 90 in order to transport article 70 through a prescribed trajectory. Where link elements 30 and 50 are not sufficiently stiff in relation to the load of article 70, either or both of the link elements may be deformed to some degree. The location signals generated at the joints and the manipulator are not responsive to such deformation. Consequently, the robot arm movement may deviate from the prescribed trajectory. Deformation can be avoided by making link elements 30 and 50 nontelescoping and sufficiently massive but this technique reduces versatility and renders the robot device more costly and more difficult to control. FIG. 2 shows in detail link element 50 arranged to detect deviations from expected locations due to deformation under load in accordance with the invention. Referring to FIG. 2, link element 50 includes directed energy light beam source 45 at end 42 and a position 5 - sensitive detector 55 at end 58. Source 45 may be an electromagnetic energy source such as a light beam source and detector 55 may be a position sensitive photodetector. Light beam source 45 may comprise a laser device or a light emitting diode and a suitable lens system for focusing light emitted therefrom. Alternatively, the light beam source may comprise a plurality of spaced independently controlled light emitting diodes and a lens system. Photodetector 55 may comprise the type S1300 nondiscrete, silicon position sensitive detector available from Hamamatsu Corporation, Middlesex, New Jersey, and described in Hamamatsu Technical Notes TN-102, January 1982. Where a light emitting diode source is used, a lens system that focuses the source light at a point on detector 55 is mounted between the source and detector. The light beam source is rigidly held in the center of end 42 by bars 227 and the position sensitive detector is centered at end 58 and rigidly held by means of bars 237. The link element is shown in FIG. 2 in its undeformed condition in which the light beam from source 45 is directed at the center of detector 55. FIG. 3 is identical to FIG. 2 except that the link element therein is shown in a deformed condition. Such deformation may be caused by the telescope construction of element 50, the weight of article 70, inertial effects during motion, or forces externally applied to article 70 by other objects.- The deformation may be the result of a force applied from any direction. As is readily seen in FIG. 1, deformation effect of the weight of article 70 may be applied out of the plane formed by links 30 and 50 and deformation can occur in element 30 or 50 or both. The bending of link element 50 ' in FIG. 3 changes the centerpoint of detector 55 with respect to the light beam from source 45 by an amount Δy and shifts the detector centerpoint by an amount ΔX.. These deviations in the position of end 58 are not reflected in the signals sent to control 90 from position sensitive apparatus normally incorporated in the articulatory joints. The circuit of FIG. 4 is adapted to generate signals Δx and Δy which are representative of the deviation of the light beam from source 45 from the centerpoint of detector 55. In FIG. 4, light source 45 comprises a light emitting diode 425 whose light output is directed through lens 470, along a line in the interior of link element 50, and through lens 475 to impinge on photodetector 55. The light beam position sensor 55 illustrated in FIG. 4 is a solid state photo detector with resistive electrodes and orthogonal pairs of low resistance contact strips. The position .information is obtained by measuring how the charge liberated by the light divides in the resistive layers. The _ position is determined by the signal currents. ( i. and i - ) flowing from contacts 437 and 439 in response to the light as: Similarly, The total photo currents ( i - + i 1 ) and (i - + i . ) are of equal magnitude and a measure of the light spot intensity. Either measure may be used to servo stabilize the light source for constant photo current, I(const.). In this way the need for division by a variable is eliminated. To obtain the position measurements, the following relationships are used: The light emitting diode (LED) is driven by a 50 percent duty cycle by the lamp current steering circuit comprising transistors 410 and 415 so that ac measurement techniques may be used to determine the light beam spot position. Oscillator 401 drives flip-flop 405 which produces a predetermined, e.g. 100 KHz, output frequency with a 50 percent duty cycle. The outputs of flip-flop 405 are used to drive the current- steering circuit and the phase sensitive detectors. The " fO output from flip- flop 405 is applied to base 412 of npn transistor 410. The fO output of flip-flop 405 is supplied to base 417 of npn transistor 415. Consequently, the current available at the emitters 418 and 413 flows through LED 425 for the half cycle daring which signal fO is positive with respect to emitter 418. The ac current signal i 1 on lead 485 is amplified in circuit 435 to produce voltage signal x1. Similarly, i _*•___ -_ * on lead 487 is amplified in circuit 445 to produce signal x2 and i -is amplified in circuit 440 to produce signal y1. The sum of the signals x1 and x2 at the outputs of amplifiers 435 and 445 correspond to the total photo current in detector 55. These signals are combined at the input of amplifier 420 via resistors 421 and 423. The output of amplifier 420 is applied to the negative input of amplifier 430 through phase sensitive detector 425 and resistor 427. The output of amplifier 430 drives the emitters 413 and 413 of the lamp steering transistors via resistor 433. In this way, a negative feedback loop is for.'._v, _._ t a the light beam intensity is maintained at the level determined by intensity control voltage VL. FIG. 8 illustrates a circuit well known in the art that may be used as a phase sensitive detector. Amplifiers 825 and 880 may be National type LF347. Switching circuit 349 may be Harris type H1-307. Referring to FIG. 8, input B receiv-_-_ ]_.r; • _>_ _i__r-nined frequency clock signal fO from flip-flop 405 and input B receives clock signal TO. During the first half of each clock cycle, signal fO is high and signal O is low so that switches 855 and 870 are open and switches 860 and 865 are closed as shown in FIG. 8. During the second half cycle, switches 855 and 870 are closed and switches 860 and 865 are closed. Assume for purposes of illustration that a signal derived from photodetector 55 in FIG. 4, e.g., a sinewave of the predetermined frequency is applied to input A with its positive half occurring when signal fO . is high. The positive going input signal is inverted in unity gain amplifier 825, passes through resistor 830 and switch 865 and is applied to the negative input of amplifier 880. Amplifier 880 reinverts the signal applied thereto so that the output signal at C is positive. In the second half cycle of the predetermined clock frequency, amplifier 825 inverts the negative half sinewave and applies its output to ground via closed switch 855. The negative half sinewave, however, is supplied to the negative input of amplifier 880 via closed switch 870. The resulting output at C is a positive half sinewave. Consequently, the circuit of FIG. 8 operates as a phase sensitive full wave rectifier whose output may be filtered to provide a dc signal corresponding to the r s value of the signal at A. Since the phase sensitive detector has a relatively narrow bandwidth, low frequency interference and high frequency noise are rejected. In the circuit of FIG. 4, the outputs of the phase sensitive detectors are dc signals corresponding to _ and y_ locations of the light beam impinging on photodetector' 55. The x1 signal from amplifier 435 is converted into a dc signal in phase sensitive detector 450 which dc signal is representative of the position of the light beam on the -- axis of detector 55. Voltage V1 from voltage source 407 is adjusted as is known in the art to provide a centering bias to amplifier 455 so that the output signal of the amplifier, ΔX, corresponds to the deviation of the light beam from the centerpoint of detector 55 along the x. axis thereof. In similar manner, signal y1 from amplifier 440 is converted into a dc signal in phase detector 460. Signal y1 is representative of the position of the light beam on the _- axis of detector 55. Voltage V2 from voltage source 407 is adjusted as is well known in the art to provide a centering bias to amplifier 465. Consequently, the output signal of amplifier 465, signal Δy, corresponds to the deviation of the light beam from the centerpoint of the photodetector along the _y_ axis thereof. Signals Δx and Δy which provide precise information on deformation of link element 50 are applied to control 90. In this way, link elements 30 and 50 may be constructed of relatively light weight materials and the loads on articulatory joints are significantly reduced without affecting article handling capability or accuracy. Detector 55 in FIG. 4 comprises an anode resistive layer 480 and a cathode resistive layer 486. The portion of the photocurrent generated in response to the beam from light source 425 appearing at the inputs of amplifiers 455 and 465 depends on the uniformity of the resistive layers. Nonuniformities in the resistive layers limit the accuracy of the beam position output signals ΔX and Δy. Greater accuracy can be obtained from the detector arrangement shown in FIG. 5 where a set of high conductivity parallel strips 505-1 through 505-7 is placed on the anode surface of the photodetector 535 and an orthogonal set of high conductivity parallel strips 507-1 through 507-7 is placed on the cathode surface of the detector. External resistors 510-1 through 510-6 are used to interconnect the anode strips and resistors 520-1 through 520-6 interconnect the cathode strips. ' For a gaussian beam of width σ, a pitch of 1.4 σ is sufficient to assure linearity of the position output signals. FIG. 6 shows another link arm light beam arrangement in which a pair of light beams are used so that the orientation of one link end with respect to the other may be determined. The light beams are turned on alternately with a 25 percent duty cycle for each, and the point at which each beam impinges on the photodetector is separately detected so that the signals from the detector apparatus are indicative of the orientation of the detector end in space with respect to the light source end. One or more of the light beam sources may be located at intermediate positions along the link to detect higher mode link motion. Referring to FIG. 6, timing generator 640 supplies signal f1 to driver 612 of semiconductor switch 610 and also supplies signal f2 to driver 617 of switch 615. Signals f1 and f2 are illustrated in waveforms 703 and 705 of FIG. 7. Responsive to signal f1 , switch element 613 is closed and switch element 614 is opened. Current of a controlled magnitude is supplied to LED 601 from intensity control amplifier 622 and a light beam of prescribed intensity is directed from LED 601 through lenses 642 and 644 to photodetector 650. In the interval during which signal f2 is on, LED 605 is enabled and current is supplied by intensity control amplifier 620 via switch element 618 so that a light beam of controlled intensity from LED 605 is directed through lenses 642 and 644 to photodetector 650. The light beam intensity is determined by voltage VD from voltage source 646. A feedback arrangement including amplifier 620 maintains the light beam intensity from LED 605 at the determined level. Similarly, a feedback arrangement including amplifier 622 maintains the light beam intensity from LED 601 at a predetermined level. Bias voltage +VB is applied to the lower edge of photodetector 650 while bias voltage -VB is applied to the left edge of photodetector 650 via resistor 658. Since the light level of each source is servo stabilized, photodetector 650 provides a signal on its left edge that is proportional to the location of an incident light beam along its horizontal or _x axis and a signal on its upper edge* is provided that is proportional to the location of an impinging light beam along its vertical or y_ axis. In the interval between t1 and -t2 in FIG. 1 , signal f1 (waveform 703) is high. LED 601 is on and the light beam therefrom impinges on detector 650. A signal representative of the x, axis location of the light beam appears on lead 654. In like manner, a signal representative of the _ axis location of the light beam appears on lead 656. The jt axis location signal from lead 654 is applied to phase sensitive detector 662 via amplifier 660, and is passed therethrough responsive to clock pulse f0. Timing signal f3 (waveform 707) is high between times t1 and t3 so that switch element 669 of semiconductor switch 665 is closed and switch element 668 is open. The phase detected signal due to _x location of the LED 601 beam is supplied to the filter formed by amplifier 670 with feedback elements 671 and 673. Consequently, signal x1 corresponding to the x_ axis location of the light beam generated by LED 601 appears at the output of amplifier 670. The signal appearing on lead 652 connected to the right edge of detector 650 in the t1-t3 interval is representative of the portion of the light beam from LED 601 not sent to the left edge. This signal is amplified by circuit 688, summed with the output of amplifier 660 and passed through phase sensitive detector 690 and semiconductor switch 692 to amplifier 694. The signal R1 from amplifier 694 corresponds to the intensity of the light beam from LED 601. The output of amplifier 694 is fed back to intensity control amplifier 622 to maintain the light beam intensity as set by voltage VD. Since the light beam intensity remains constant, the x1 signal is representative of the _x axis location of the impinging light beam and the y1 signal is representative of the y; axis location of the impinging light beam from 601. Between times t1 and t3 in FIG. 7, signal f3 is high. Consequently, the output of phase sensitive detector 676 is connected via closed switch 682 to the input of filter circuit 684 whose output y1 represents the y_ location of the light beam spot due to LED 601. During the time period between t3 and t4, LED activating signal f2 (waveform 705) is on and signal f1 (waveform 703) is off. LED 605 is activated through semiconductor switch 615 and the light beam therefrom is directed toward photodetector 650. Signal f3 (waveform 707) is low so that the left edge signal on lead 654 passes through phase sensitive detector 662, semiconductor switch element 668 and amplifier 672. The output of amplifier 672, signal x2, is representative of the axis location of the light beam from LED 605. The right edge signal from photodetector 650 between times t3 and t5 passes through phase sensitive detector 690, switch element 691, and amplifier 696. The R2 signal from amplifier 696 is used to maintain the intensity of the light beam from LED 605 constant. Between times t3 and t5, signal f3 is off whereby the upper edge signal from photodetector 650 appearing on lead 656 passes through phase sensitive detector 676, switch element 681, and amplifier 686. The y2 output of amplifier 686 is therefore representative of the _y_ axis location of the light beam from LED 605. The operations of the circuit of FIG. 6 are repeated responsive to the timing control signals of FIG. 7 so that signals x1 , y1 , x2 and y2 corresponding to the locations of the alternating light beams from LEDs 601 and 605 are supplied to control arrangement of the robotic structure. These beam location signals are indicative of the relative orientations of the link arm ends and reflect link arm deformations due to bending and torsional deformation. The invention has been shown and described with reference to particular embodiments thereof. It should be understood that the embodiments disclosed herein are merely exemplary of the invention and that various modifications and changes may be made by those skilled in the art without departing from the spirit and scope of the invention. For example, the positions of the light beam source and the light beam position detector could be reversed so that the source is at the second end of the link while the detector is at the first link end. The source need not be located at the end but at some intermediate point along the link and the detector may be located at a more convenient point along the link other than at an end. Alternatively, both the light beam source and detector may be located at the same point along the link and a mirror arrangement may be operative to reflect the light beam at one end of the link,

Claims: - 14 - Claims 1. An article handling structure comprising: a link arm having first and second ends; CHARACTERIZED BY means for determining the orientation of said second end relative to said first end; said orientation determining means including, a light beam source mounted on the first link end for directing at least one light beam to said second end; and a light beam detector mounted on said second end responsive to said light beam for producing at least one signal representative of the orientation of the second end with respect to said light beam source. 2. An article handling structure according to claim 1 , FURTHER CHARACTERIZED BY control means responsive to the orientation representative signal for altering the orientation of said second end. 3. An article handling structure according to claim 1 , CHARACTERIZED IN THAT the light beam source comprises means for directing a plurality of light beams along the link arm to the second end; and the light beam detecting means comprises means responsive to each light beam for generating a signal representative of the position the light beam impinges on the second end. 4. An article handling structure according to claim 3, CHARACTERIZED IN THAT the light beam source further comprises means for directing one of the plurality of light beams at a time along the link arm to the second end; and the light beam . detecting means further comprises means responsive to each directed light beam for generating a signal representative of the position the directed light beam impinges on the second end. 5. An article handling structure according to claim 4, CHARACTERIZED IN THAT the means for directing a plurality of light beams comprises means for directing a pair of light beams along the link arm to the second end. 6. An article handling structure according to claim 1 , CHARACTERIZED IN THAT the light beam detector on the second link end comprises a sheet of photosensitive material; means responsive to the light beam impinging on the photosensitive sheet for generating a first signal representative of the impinging position of the light beam along a first predetermined axis; and means responsive to the light beam from the source impinging on the photosensitive sheet for generating a second signal representative of the impinging position along a second predetermined axis. 7. An article handling structure according to claim 6, CHARACTERIZED IN THAT the first and second signal generating means comprises means for producing a signal representative of the position of the centroid of the impinging light beam. 8. An article handling structure according to claim 7, CHARACTERIZED IN THAT the photosensitive sheet comprises a set of spaced photosensitive strips substantially parallel to the first axis and a set of spaced photosensitive strips substantially parallel to the second axis. 9. An article handling structure according to claim 1 , CHARACTERIZED IN THAT the link arm comprises a hollow link element; that the light beam source is adapted to direct a light beam along the interior of the hollow link element; and that the light beam detector is adapted to detect the position of the light beam in the interior of the hollow link element. 10. An article handling structure according to any of the preceding claims 1-9, CHARACTERIZED IN THAT the link arm comprises a plurality of elements in telescoping relationship. 11. A robotic type structure comprising: a link arm having first and second ends; means for determining the relative positions of the first and second ends; the relative position determining means including, an electromagnetic beam source mounted on the first link end for directing at least one light beam to a predetermined position on the second end when the second end is in its unloaded condition; an electromagnetic beam detector mounted on the second end adapted to produce a signal representative of deviation of the second end from its unloaded condition responsive to the electromagnetic beam; and control means responsive to the deviation representative signal for repositioning the link arm to compensate for the link arm loading. 12. A robotic type structure according to claim 11 , CHARACTERIZED IN THAT the electromagnetic beam is a light beam and the electromagnetic beam source is a light beam source. 13. A robotic type structure according to claim 12, - 1 7 - CHARACTERIZED IN THAT the light beam detector on the second link end comprises a sheet of photosensitive material; means responsive to the light beam impinging on the photosensitive sheet for generating a first signal representative of the impinging position of the light beam along a first predetermined axis; and means responsive to the light beam from the source impinging on the photosensitive sheet for generating a second signal representative of the impinging position along a second predetermined axis. 14. A robotic type structure according to claim 13, CHARACTERIZED IN THAT the first and second signal generating means comprises means for producing a signal representative of the position of the centroid of the impinging light beam. 15. A robotic type structure according to claim 14, CHARACTERIZED IN THAT the photosensitive sheet comprises a set of spaced photosensitive strips substantially parallel to the first axis and a set of spaced photosensitive strips substantially parallel to the second axis. 16. A robotic type structure according to claim 12, CHARACTERIZED IN THAT the link arm comprises a hollow link element; the light beam source is adapted to direct a light beam along the interior of the hollow link element; and the light beam detector is adapted to detect the position of the light beam in the interior of the hollow link element. 17. A robotic type structure according to any of claims 11-16, CHARACTERIZED IN THAT the link arm comprises a plurality of elements in telescoping relationship. 18. A robotic type structure comprising: a linking element having first and second ends; means for determining the orientation of the second end relative to the first end; at least one directed energy beam source mounted along the linking element for transmitting a directed energy beam to the second end; and a position sensitive energy beam detector mounted along the linking element responsive to the directed energy beam for producing a signal representative of the orientation of the second end with respect to the directed energy beam source. 19. A robotic type structure according to claim 1, CHARACTERIZED IN THAT .the directed energy beam is an electromagnetic energy beam and the directed energy beam source is an electromagnetic energy beam source. 20. A robotic type structure according to claim 19, CHARACTERIZED IN THAT the electromagnetic beam is a light beam and the electromagnetic beam source is a light beam source.

Inventors: BOIE ROBERT ALBERT, BOIE, ROBERT, ALBERT
Applicants: AMERICAN TELEPHONE & TELEGRAPH, AMERICAN TELEPHONE & TELEGRAPH COMPANY
Application year: 1985
Main classification: B25J13
IPC codes: B25J9, B25J13, B25J18, B25J19