Method and apparatus for positioning a robotic end effector

• US 4,980,626 A
• Filed: 08/10/1989
• Issued: 12/25/1990
• Est. Priority Date: 08/10/1989
• Status: Expired due to Fees

• Current Assignee: The United States of America As Represented By The Secretary of Agriculture
• Original Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Inventors: Hess, Clifford W., Li, Larry C. H.
• Primary Examiner(s): Shoop, Jr., William M.
• Assistant Examiner(s): Ip, Paul
• Application Number:
  US07/392,235
• Time in Patent Office: 502 Days
• Field of Search: 318/560-573, 318/630-632, 318/640, 364/513, 901/30-37, 901/46, 901/47
• US Class Current: 318/568.16
• CPC Class Codes: B25J 13/081 Touching devices, e.g. pressure-sensitive
• CPC Class Codes: B25J 15/0009 comprising multi-articulated fingers, e.g. resembling a human hand
• CPC Class Codes: B25J 9/1005 comprising adjusting means
• CPC Class Codes: Y10S 294/907 Sensor controlled device

Abstract

A robotic end effector and operation protocol provide for a reliable grasp of a target object irrespective of the target'"'"'s contours. A robotic hand 30 includes a plurality of jointed fingers 31-34, one of which, like a thumb 31, is in opposed relation to the other. Each finger comprises at least two jointed sections, and is provided with reflective proximity sensors, one on the inner surface of each finger section. Each proximity sensor comprises a transmitter of a beam of radiant energy and a receiver for receiving reflections of the transmitted energy when reflected by a target object. On the fingers opposed to the thumb, the proximity sensors 41 on the outermost finger sections are aligned in an outer sensor array and the sensors 42 on the intermediate finger sections and sensors 43 on the innermost finger sections are similarly arranged to form an intermediate sensor array and an inner sensor array, respectively. The invention includes a computer system 55 with software and/or circuitry 56 for a protocol comprising the steps in sequence of (1) approach axis alignment to maximize the number of outer layer sensors which detect the target; (2) non-contact contour following of the target by the robot fingers to minimize target escape potential; and (3) closing to ridigize the target including dynamically re-adjusting the end effector finger alignment to compensate for target motion. A signal conditioning circuit 52 and gain adjustment 57 are included to maintain the dynamic range of low power reflection signals.

Claims

1. A system for positioning a dexterous robotic end effector to minimize target escape potential during grasping, said system comprising:

a robotic end effector in the form of a robotic hand having a plurality of jointed fingers with at least one of said fingers mounted in opposed relation to the others, each said finger comprised of joined segments;

a plurality of reflective proximity sensors for transmitting a plurality of radiant energy beams and for detecting reflected echoes of said energy beams, said proximity sensors arranged such that one of said sensors is mounted on the inner surface of each finger segment and the proximity sensors on the outermost finger segments of the fingers opposed to said one finger are aligned in linear array to form an outer layer of proximity sensors and the proximity sensors on the finger segments next adjacent to the outermost segments are aligned in linear array to form an inner layer of proximity sensors; and

control means for guiding said robotic hand in proximity to a target to be grasped thereby and responsive to reflections of the energy beams when intercepted and reflected by a target object for generating electrical signals representing range to target from each proximity sensor detecting a reflection of its energy beam from said target and in response to said signals aligning the approach axis of said robotic hand to the target to maximize the number of outer layer sensors which detect the target, said control means including means for guiding the fingers of the robotic hand to follow the contours of the target in non-contact relation therewith in a trapping movement to minimize target escape potential and following said trapping movement, actuating the robot fingers to close and rigidize the target.

2. A system for positioning a dexterous robotic end effector as set forth in claim 1 further including means for dynamically re-adjusting the end effector alignment with respect to the target during the act of grasping the target.

3. A system for positioning a dexterous robotic end effector as set forth in claim 1 further including means for adjusting the signal strength of said range signals in correspondence with target distance to maintain the dynamic range of a low powered reflection signal.

4. A system for positioning a dexterous robotic end effector as set forth in claim 1 wherein said proximity sensors transmit and detect optical beams of radiant energy.

5. A system for positioning a dexterous robotic end effector as set forth in claim 1 wherein said proximity sensors transmit and detect beams of ultrasonic energy.

6. A system for positioning a dexterous robotic end effector to minimize target escape potential during grasping, said system comprising:

a robotic end effector in the form of a robotic hand having a plurality of articulated fingers with one of said fingers mounted in opposed relation to the others, each said finger comprised of joined segments;

a plurality of proximity sensors for transmitting a plurality of radiant energy beams and for detecting reflected echoes of said energy beams, said proximity sensors being arranged such that one of said sensors is mounted on the inner side of each finger segment and the proximity sensors on the outermost finger segments of the fingers opposed to said one finger are aligned to form an outer array of proximity sensors and the proximity sensors on the finger segments next adjacent to the outermost segments are aligned to form an inner array of proximity sensors; and

control means for guiding said robotic hand in proximity to a target to be grasped thereby and responsive to reflections of the energy beams when intercepted and reflected by the target object for aligning the approach axis of said robotic hand to the target to maximize the number of outer array sensors which detect the target, said control means including means for guiding the fingers of the robotic hand to follow the contours of the target in non-contact relation therewith in a trapping movement to minimize target escape potential and following said trapping movement, actuating the robot fingers to close and rigidize the target.

7. A system for positioning a dexterous robotic end effector as set forth in claim 6 further including means for dynamically re-adjusting the end effector alignment with respect to the target during the act of grasping the target.

8. A system for positioning a dexterous robotic end effector as set forth in claim 6 wherein said proximity sensors transmit and detect optical beams of radiant energy.

9. A system for positioning a dexterous robotic end effector as set forth in claim 6 wherein said proximity sensors transmit and detect beams of ultrasonic energy.

10. A system for positioning a robotic end effector to minimize target escape potential during grasping, said system comprising:

a robotic end effector having a plurality of fingers with one of said fingers mounted in opposed relation to another of said fingers;

a plurality of proximity sensors for transmitting a plurality of radiant energy beams, said proximity sensors arranged such that at least two of said sensors are mounted on the inner surface of each finger in spaced relation to one another in the longitudinal axial direction of the finger and the outermost proximity sensors on the fingers are aligned in linear array to form an outer layer of proximity sensors and the proximity sensors next adjacent to the outermost sensors are aligned in linear array to form an inner layer of proximity sensors; and

control means for guiding said robotic end effector in proximity to a target to be grasped thereby and responsive to reflections of the energy beams when intercepted and reflected by a target object for aligning the approach axis of said robotic end effector to the target to maximize the number of outer layer sensors which detect the target, said control means including means for guiding the fingers of the robotic and effector to follow the contours of the target in non-contact relation therewith in a trapping movement which minimizes target escape potential and following said trapping movement, actuating the fingers to close and rigidize the target.

11. A system for positioning a robotic end effector as set forth in claim 10 further including means for dynamically re-adjusting the end effector alignment with respect to the target during the act of grasping the target.

12. A system for positioning a robotic end effector as set forth in claim 10 wherein said control means includes means for generating electrical signals representing range to target from each proximity sensor detecting a reflection of its energy beam from said target, and means for adjusting signal strength of said range signals in correspondence with target distance so as to maintain the dynamic range of a low powered reflection signal.

13. A method for positioning a dexterous robotic end effector to minimize target escape potential during grasping, wherein the robotic and effector is in the form of a robotic hand having a plurality of jointed fingers with one of said fingers mounted in opposed relation to the others, and each said finger is comprised of joined segments, said method comprising the steps of:

utilizing a plurality of reflective proximity sensors for transmitting a plurality of radiant energy beams and for detecting reflected echoes of said energy beams and arranging said proximity sensors such that one of said sensors is mounted on the inner surface of each finger segment and the proximity sensors on the outermost finger segments of the fingers opposed to said one finger are aligned in linear array to form an outer layer of proximity sensors and the proximity sensors on the finger segments next adjacent to the outermost segments are aligned in linear array to form an inner layer of proximity sensors;

guiding said robotic hand in proximity to a target to be grasped in response to reflections of the energy beams when intercepted and reflected by a target object by aligning the approach axis of said robotic hand to the target to maximize the number of outer layers which detect the target; and

controlling the fingers of the robotic hand to follow the contours of the target in non-contact relation therewith in a trapping movement to minimize target escape potential and following said trapping movement, actuating the robot fingers to close and rigidize the target.

14. A method for positioning a robotic end effector to minimize target escape potential during grasping, wherein the robotic end effector is equipped with a plurality of fingers with one of said fingers mounted in opposed relation to another of said fingers, said method comprising the steps of:

utilizing a plurality of reflective proximity sensors for transmitting a plurality of radiant energy beams and for detecting reflected echoes of said energy beams in an arrangement of said proximity sensors such that one of said sensors is mounted on the inner surface of each finger segment and the proximity sensors on the outermost finger segments of the fingers opposed to said one finger are aligned in linear array to form an outer layer of proximity sensors and the proximity sensors on the finger segments next adjacent to the outermost segments are aligned in linear array to form an inner layer of proximity sensors;

guiding said robotic hand in proximity to a target to be grasped in response to reflections of the energy beams when intercepted and reflected by a target object by aligning the approach axis of said robotic hand to the target to maximize the number of outer layers which detect the target; and

controlling the fingers of the robotic hand to follow the contours of the target in non-contact relation therewith in a trapping movement which minimizes target escape potential and following said trapping movement, actuating the robot fingers to close and rigidize the target.

15. A method for positioning a robotic end effector to minimize target escape potential during grasping as set forth in claim 14 which further includes the step of dynamically re-adjusting the end effector alignment with respect to the target during the act of grasping to compensate for target motion.