WO1992005016A1 - Procedes et appareil de compensation passive des effets de la gravite sur des structures articulees - Google Patents

Procedes et appareil de compensation passive des effets de la gravite sur des structures articulees Download PDF

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Publication number
WO1992005016A1
WO1992005016A1 PCT/US1991/006679 US9106679W WO9205016A1 WO 1992005016 A1 WO1992005016 A1 WO 1992005016A1 US 9106679 W US9106679 W US 9106679W WO 9205016 A1 WO9205016 A1 WO 9205016A1
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WO
WIPO (PCT)
Prior art keywords
pulley
tendon
force
link
joint
Prior art date
Application number
PCT/US1991/006679
Other languages
English (en)
Inventor
Nathan T. Ulrich
Vijay Kumar
Original Assignee
The Trustees Of The University Of Pennsylvania
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by The Trustees Of The University Of Pennsylvania filed Critical The Trustees Of The University Of Pennsylvania
Publication of WO1992005016A1 publication Critical patent/WO1992005016A1/fr

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23Q—DETAILS, COMPONENTS, OR ACCESSORIES FOR MACHINE TOOLS, e.g. ARRANGEMENTS FOR COPYING OR CONTROLLING; MACHINE TOOLS IN GENERAL CHARACTERISED BY THE CONSTRUCTION OF PARTICULAR DETAILS OR COMPONENTS; COMBINATIONS OR ASSOCIATIONS OF METAL-WORKING MACHINES, NOT DIRECTED TO A PARTICULAR RESULT
    • B23Q11/00—Accessories fitted to machine tools for keeping tools or parts of the machine in good working condition or for cooling work; Safety devices specially combined with or arranged in, or specially adapted for use in connection with, machine tools
    • B23Q11/001—Arrangements compensating weight or flexion on parts of the machine
    • B23Q11/0017—Arrangements compensating weight or flexion on parts of the machine compensating the weight of vertically moving elements, e.g. by balancing liftable machine parts
    • B23Q11/0021—Arrangements compensating weight or flexion on parts of the machine compensating the weight of vertically moving elements, e.g. by balancing liftable machine parts the elements being rotating or pivoting
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
    • B25J—MANIPULATORS; CHAMBERS PROVIDED WITH MANIPULATION DEVICES
    • B25J19/00—Accessories fitted to manipulators, e.g. for monitoring, for viewing; Safety devices combined with or specially adapted for use in connection with manipulators
    • B25J19/0008—Balancing devices
    • B25J19/0016—Balancing devices using springs

Definitions

  • the present invention relates to articulated structures comprised of one or more links serially connected by rotatable joints. More specifically, the present invention relates to methods and apparatus for compensating for the effects of gravity acting upon an articulated structure undergoing manipulation.
  • Articulated structures including robotic manipulators, often comprise distinct members or "links" which are serially connected and manipulated by the activation of one or more rotatable joints which connect the links to a base, foundation or “platform.”
  • the rotatable joints actuated by a cable or tendon.
  • the human finger itself is a collection of serial links, connected at rotatable joints and activated by the force of tendons.
  • a finger within this class is disclosed in U.S. Patent 4,957,320 which is assigned to the assignee of the present invention and is incorporated herein by reference.
  • Other examples include the operative booms of cranes and other construction equipment and the structures which support X-ray equipment, television cameras, lamps, dental drills and a variety of other objects which must be moved through space.
  • the gravity-induced joint loads referred to herein describe the loads placed upon a joint due to the weight of the manipulating apparatus itself, i.e., the mass of the links under the acceleration due to gravity. Because serial linkages tend to propagate increasing forces back through the mechanism, gravity loading can, in many cases, account for more than 50% of the available actuator torque at the base links. Even in static configurations, large amounts of power can be consumed simply in resisting gravitational forces, with attendant decreases in available payload and efficiency.
  • the actuator power required to resist joint torques caused by the weight of links can be a significant problem. It would be desireable to provide a mechanical method to counteract gravity-induced joint torques, a technique which is passive, energy-conservative, and easily adapted to many kinematic configurations.
  • Another common method of gravity compensation involves inclusion of the gravity-induced joint torque in the solution of the equations of motion, the subsequent provision of control compensation using the joint actuators.
  • this solution results in degraded manipulator performance or necessitates larger actuators, transmissions, and structure.
  • the power requirement is also concomitantly increased, since motor current is required to resist gravity, even in static configurations.
  • Another object of the present invention is to present a system whereby multiple serial linkages which lie in more than one plane within an articulated member may be gravity compensated.
  • an articulated structure comprising a first link, a platform and a first rotatable joint connecting the proximal end of the first link and the platform, and comprising an eccentric pulley means and a compliant tendon means for resisting the rotation of the eccentric pulley.
  • the compliant tendon is connected to the eccentric pulley to compensate for the force created by the weight of the link, thereby reducing the force required to move the distal end of the link through space.
  • the compliant tendon creates a force directly proportional to the change in its length and the pulley converts the force created by the tendon into a non-linear compensation torque which varies with the relative position of the link to effectively compensate for the force due to gravity.
  • the magnitude of the non-linear compensation torque is the mathematical product of the payload, the length of the link and the cosine of the angle between the link and the vertical .
  • the radius of the pulley varies as a function of angular displacement about the rotational axis of the pulley and the function which describes the radius of the pulley, r p ( ⁇ ), is:
  • the present invention provides apparatus in which one or more links are connected in series by one or more joints; the axes of rotation of the joints are perpendicular to the direction of gravitational acceleration and pulleys and tendons are connected to at least one of the joints.
  • the tendons are connected to the joint in tension and thus the force created by the pulley and tendon compensates for the force created by gravitational acceleration acting upon the links.
  • the multiplicity of joints and the planes in which such joints lie results in apparatus comprising a plurality links connected in series by one or more rotational joints, wherein the torque produced at each joint is created by the relative position of the links and is described by the product of two or more joint angles by providing one or more pulley means and tendon means for actuating at least one of the joints.
  • the pulley and tendon again compensate for the force created by gravitational acceleration acting upon the links.
  • the torque produced at one or more of the joints can be expressed as a function of the sum of two or more joint angles and the tendon and pulley provide a resistive force to compensate for the torque produced, the compensating force varying as a function of angular displacement of one or more of the joints. In any event, however, the compensating force created at each joint varies only with the angular displacement of the joint.
  • FIG. 1 is a side elevational view of a simplified single link, single joint gravity compensated manipulator made in accordance with the present invention.
  • FIG. 2 illustrates the relationship between the effective radius of a pulley and the actual radius of a pulley.
  • FIG. 3 provides a comparison between an ideal gravity compensation eccentric pulley and a circular pulley.
  • FIG. 4 is a partially diagrammatic side view of a single link manipulator which can be gravity compensated in accordance with the present invention.
  • manipulators or other articulated members which utilize cables or "tendons" to actuate one or more of the joints between serially connected links.
  • manipulators generally operate and the details of active and passive control of one or more joints by adjusting the tension of one or more tendons or otherwise causing the tendons to impart rotation upon pulleys.
  • the present invention is applied to manipulators which utilize tendon actuation as the source of manipulation for at least one joint.
  • FIG. 1 there is illustrated a single joint manipulator made in accordance with the present invention.
  • An eccentric pulley 100 is rotatably attached to a platform or base 50.
  • a compliant tendon 110 is passed over the pulley 100 and is also affixed to the platform 50.
  • Extending from the joint attached to the pulley 100 is a link 120.
  • the proximal end of the link is affixed to the pulley, while the distal end carries a payload 52.
  • the payload 52 creates & downward force "mg" equal in magnitude to its mass multiplied by the acceleration of gravity and acting in the direction shown.
  • the angular displacement of the link 120 about the axis of the pulley 100 is measured by the angle ⁇ , as illustrated.
  • the link 120 is assumed to be massless and infinitely stiff, with the payload 52 of mass m located at the endpoint a distance L from the axis of the rotational joint 100.
  • the gravity-induced torque at the joint 100 can be expressed as:
  • a gravity-compensation method will exactly compensate for this torque without additional energy input.
  • the combination of a compliant tendon 110 and an eccentric pulley 100 can achieve this result.
  • a compliant tendon will generally act as a spring and create a resistive force generally directly proportional to the displacement of the member.
  • T is the difference in tension between the two tendons
  • r is the effective radius of the pulley 100 (which is assumed to be symmetric such that the distance between the two tendons is 2r)
  • the tendon 110 itself for purposes of illustration is shown in an embodiment including two springs 112,114; k is the spring constant associated with the two springs 112,114 and x is the linear displacement of the tendon 110.
  • the actual shape of an eccentric pulley 100 made in accordance with this equation may be compared to the profile of a circular pulley, shown in phantom. Surprisingly, the profiles are identical to within 1.5% over a range of 180o of the perimeter.
  • FIG. 4 there is illustrated a partially diagrammatic representation of a portion of a robotic manipulator to which the gravity compensation system of the present invention may be applied.
  • Gravity compensation as defined above for a single-link arm can be easily extended to multiple links when the joint axes remain perpendicular to the direction of gravitational acceleration.
  • the so-called "elbow” manipulator of which the Puma series built by Unimation Corporation (USA) is a common example, has just this type of configuration.
  • FIG. 4 Consider a free-body diagram of one link in such a kinematic chain, as shown in FIG. 4.
  • the proximal joint 200 of this link 220 is actuated by tendons 210 parallel to a line connecting this joint axis with the previous joint axis (not shown) and with tensions T 1 and T 2 .
  • a payload weight 52 m j +1 g is supported at the distal end.
  • the link has a mass m jg and a center of mass located a distance L cm,j from the proximal joint axis.
  • the reaction force at the proximal joint bearings can be decomposed into components perpendicular and parallel to the previous link, represented by the arrows R P and R N shown in FIG. 4.
  • R N (m j + m j+1 ) g cos ⁇ j-1
  • ⁇ j-1 m j-1 gL cm,j-1 COS ⁇ j-1 + (m j + m j+1 ) gL j-1 COS ⁇ j-1 which is only dependent upon ⁇ j-1 , as the same analysis can be extended for all other joints in a system.
  • the gravitationally-induced torque at each joint varies only with its displacement, and not with distal joint positions.
  • each joint may be independently compensated for the effects of gravity using the same method that was derived earlier for a single joint such as that illustrated in FIG. 1, where the mass of all distal links is assumed to be concentrated at the outboard joint axis.
  • This behavior occurs when joints are actuated by tension elements and cables routed to the base frame.
  • this has further significance from a kinematic, dynamic, and control standpoint, the impact of which will be readily apprehended by those of ordinary skill.
  • the present invention finds applicability in manipulator systems beyond the single joint and "elbow" configurations described above in relation to FIGS. 1 and 2 respectively.
  • these other kinematic configurations require more complicated approaches.
  • a kinematic skeleton for an arm can be envisioned which has similar degrees of freedom as are found in the human arm.
  • the arm illustrated is a generalized representations of the arm known as the "MIT/WAN" arm, disclosed in Salisbury,
  • the arm is comprised of the three joints and also provides a further axis of rotation along the longitudinal axis of one of the links .
  • the gravity-induced torques at each of the joints are:
  • ⁇ 1 (m 3 gL 1 + m 1 gL ca1 ) cos ⁇ 1
  • ⁇ 2 (m 3 gL cm3 COS ⁇ 1 + ⁇ 3 ) cos ⁇ 2
  • ⁇ 2 and ⁇ 3 involve products of several joint angles and cannot be compensated for using the simple method described earlier.
  • trigonometric identifies we can express them as cosine functions of various sums of joint angles: ⁇ 2 - m 3 gL cm3 [ cos ( ⁇ 2 + ⁇ 3 ) + cos ( ⁇ 1 + ⁇ 2 - ⁇ 3 )
  • ⁇ 3 m 3 gL cm3 [cos ( ⁇ 1 - ⁇ 2 + ⁇ 3 ) + cos ( ⁇ 1 + ⁇ 2 ⁇ 3 )]
  • the torques induced by gravity at each joint can be determined for any kinematic configuration. In general, they will be expressions which involve trigonometric functions of several joint displacements. Although it is theoretically possible to synthesize a mechanical calculator which will allow the application of the gravity compensation method described here, whether the resulting complexity is justified upon the application.
  • the present invention thus provides simple mechanical method for passively compensating for gravitationally-induced joint torques.
  • the methods and apparatus can be easily applied to specific kinematic configurations.
  • Other manipulator designs require more complicated approaches.
  • a single-joint embodiment has been constructed and proven that the methods disclosed herein are effective.
  • the present invention discloses a unique manner in which the linear function of spring force may be converted to a force curve varying according to a sine function, which accurately compensates for the varying loading which a force being manipulated by a link connected to a rotating joint exerts.
  • Theoretical equations provide a model system which permits an idealized eccentric pulley profile to be designed.
  • the present invention provides an efficient mechanism whereby the effective payload of a manipulator can be increased. By substantially removing the weight of the manipulator arm itself, the effects of this force upon the overal system is reduced. In conventional robotic manipulators, up to 70% of the maximum useful torque is required merely to hold the manipulator in certain positions.
  • the need for this torque is substantially eliminated using the present invention since the weight of the manipulator arm itself does not act through one of the joints.
  • the use of the present invention will also improve the dynamic performance of manipulators since inertial effects due to the weight of the links may be substantially reduced, since the actuators and motors can be made smaller, permitting greater speed and precision.
  • the present invention will be preferably applied to those manipulators in which the torque required to drive the joints is a limiting factor, or where the lower efficiency of utilization of the power input to the joints is a problem. Moreover, since the present invention permits smaller and less expensive drive mechanisms and actuators to be used, both the cost of the manipulator apparatus itself and the expenses related to its operation are reduced.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Robotics (AREA)
  • Manipulator (AREA)

Abstract

L'invention concerne des procédés et un appareil permettant de compenser le poids d'un manipulateur articulé. On peut compenser les effets de la gravité s'exerçant sur de manipulateurs qui emploient une ou plusieurs liaisons (120) reliées en série par des articulations rotatives et qui comprennent des éléments de précontrainte (112, 114) et des câbles (110) dans le système de commande, en utilisant une poulie d'excentrique (100) choisie spécialement pour transformer la force linéaire créée par la tension des éléments de précontrainte en un couple de résistance non linéaire qui contrebalance le couple créé par le poids de l'appareil sur toute la plage de mouvement. Des modes d'exécution simplifiée à une seule liaison et à plusieurs liaisons sont également décrits. L'invention concerne en outre des procédés permettant de compenser les effets de la gravité.
PCT/US1991/006679 1990-09-14 1991-09-13 Procedes et appareil de compensation passive des effets de la gravite sur des structures articulees WO1992005016A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US58249890A 1990-09-14 1990-09-14
US582,498 1990-09-14

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WO1992005016A1 true WO1992005016A1 (fr) 1992-04-02

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Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5402690A (en) * 1992-09-30 1995-04-04 Mitsubishi Denki Kabushiki Kaisha Robot
NL1010446C2 (nl) * 1998-11-02 2000-05-03 Exact Dynamics B V Manipulator.
WO2001085403A1 (fr) * 2000-05-12 2001-11-15 Renishaw Plc Mecanisme de contrepoids de stylet pour sonde de mesure
US6899308B2 (en) 2003-07-31 2005-05-31 Agency For Science, Technology And Research Passive gravity-compensating mechanisms
EP1876505A1 (fr) * 2006-07-03 2008-01-09 Force Dimension S.à.r.l Compensation gravitationnelle d'un dispositif haptique
US8667860B2 (en) 2006-07-03 2014-03-11 Force Dimension S.A.R.L. Active gripper for haptic devices
JP2017030099A (ja) * 2015-08-03 2017-02-09 パスカルエンジニアリング株式会社 ロボット用バランサ装置

Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SU480538A1 (ru) * 1973-07-25 1975-08-15 Экспериментальный научно-исследовательский институт кузнечно-прессового машиностроения Система управлени копирующего манипул тора
DD200370A1 (de) * 1981-09-15 1983-04-20 Peter Otto Vorrichtung an gelenkverbindungen von manipulatoren fuerden gewichtsausgleich
US4500251A (en) * 1982-02-05 1985-02-19 Mitsubishi Denki Kabushiki Kaisha Multijoint manipulator
DD219427A1 (de) * 1983-12-02 1985-03-06 Bauakademie Ddr Vorrichtung zum schwerkraftmomenten ausgleich der drehgelenke von robotern
SU1426782A1 (ru) * 1987-03-03 1988-09-30 Московский станкоинструментальный институт Манипул тор
US4784010A (en) * 1987-04-27 1988-11-15 Graco Robotics Inc. Electric robotic work unit
SU1458216A1 (ru) * 1987-05-19 1989-02-15 Смоленское Научно-Производственное Объединение "Техноприбор" Механизм уравновешивани манипул тора
EP0316531A1 (fr) * 1987-11-17 1989-05-24 Mitsubishi Jukogyo Kabushiki Kaisha Dispositif d'équilibrage pour robot industriel

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SU480538A1 (ru) * 1973-07-25 1975-08-15 Экспериментальный научно-исследовательский институт кузнечно-прессового машиностроения Система управлени копирующего манипул тора
DD200370A1 (de) * 1981-09-15 1983-04-20 Peter Otto Vorrichtung an gelenkverbindungen von manipulatoren fuerden gewichtsausgleich
US4500251A (en) * 1982-02-05 1985-02-19 Mitsubishi Denki Kabushiki Kaisha Multijoint manipulator
DD219427A1 (de) * 1983-12-02 1985-03-06 Bauakademie Ddr Vorrichtung zum schwerkraftmomenten ausgleich der drehgelenke von robotern
SU1426782A1 (ru) * 1987-03-03 1988-09-30 Московский станкоинструментальный институт Манипул тор
US4784010A (en) * 1987-04-27 1988-11-15 Graco Robotics Inc. Electric robotic work unit
SU1458216A1 (ru) * 1987-05-19 1989-02-15 Смоленское Научно-Производственное Объединение "Техноприбор" Механизм уравновешивани манипул тора
EP0316531A1 (fr) * 1987-11-17 1989-05-24 Mitsubishi Jukogyo Kabushiki Kaisha Dispositif d'équilibrage pour robot industriel

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5402690A (en) * 1992-09-30 1995-04-04 Mitsubishi Denki Kabushiki Kaisha Robot
NL1010446C2 (nl) * 1998-11-02 2000-05-03 Exact Dynamics B V Manipulator.
WO2000025989A1 (fr) * 1998-11-02 2000-05-11 Exact Dynamics B.V. Manipulateur
US6923613B2 (en) 1998-11-02 2005-08-02 Henricus Johannes Adrianus Stuyt Manipulator
WO2001085403A1 (fr) * 2000-05-12 2001-11-15 Renishaw Plc Mecanisme de contrepoids de stylet pour sonde de mesure
US6899308B2 (en) 2003-07-31 2005-05-31 Agency For Science, Technology And Research Passive gravity-compensating mechanisms
EP1876505A1 (fr) * 2006-07-03 2008-01-09 Force Dimension S.à.r.l Compensation gravitationnelle d'un dispositif haptique
WO2008003417A1 (fr) * 2006-07-03 2008-01-10 Force Dimension S.A.R.L. Compensation de gravité pour dispositif haptique
US8188843B2 (en) 2006-07-03 2012-05-29 Force Dimension S.A.R.L. Haptic device gravity compensation
US8667860B2 (en) 2006-07-03 2014-03-11 Force Dimension S.A.R.L. Active gripper for haptic devices
JP2017030099A (ja) * 2015-08-03 2017-02-09 パスカルエンジニアリング株式会社 ロボット用バランサ装置

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