Safe Collaborative Gripping Device

Abstract

A method for controlling a gripping device (2) for a robot (20) comprising two or more gripping structures (4, 4′) movably arranged relative to each other and being configured to grip an object (8, 16) is disclosed. The method comprises actively restricting the displacement (ΔD) of at least one of the two or more gripping structures so that said displacement is less than or equal to a predefined maximum displacement (ΔD.sub.max). The method comprises the steps of detecting when at least one of the gripping structures is in contact with the object and increasing the force (F) exerted by at least one of the two or more gripping structures to the object from a predefined first level (F.sub.1) to a predefined second level (F.sub.2) when it has been detected that at least one of the two or more gripping structures is in contact with the object.

Claims

1. A method for controlling a gripping device for a robot comprising two or more gripping structures movably arranged relative to each other and configured to grip an object, the method comprising: actively restricting a displacement (ΔD) of at least one of the two or more gripping structures so that said displacement (ΔD) is less than or equal to a predefined maximum displacement (ΔD.sub.max); detecting when at least one of the two or more gripping structures is in contact with the object; and increasing a force (F) exerted by at least one of the two or more gripping structures to the object from a predefined first level (F.sub.1) to a predefined second level (F.sub.2) when it has been detected that at least one of the two or more gripping structures is in contact with the object.

2. The method according to claim 1, wherein a ratio between the predefined second level (F.sub.2) and the predefined first level (F.sub.1) is at least 2.0.

3. The method according to claim 1, wherein the step of increasing the force (F) from the predefined first level (F.sub.1) to the predefined second level (F.sub.2) occurs linearly as a function of the displacement of at least one of the two or more gripping structures.

4. The method according to claim 1 further comprising the steps of: a) detecting when at least one of the two or more gripping structures has been in contact with the object for a predefined time period; and b) only increasing the force (F) exerted by at least one of the two or more gripping structures to the object if at least one of the two or more gripping structures has been in contact with the object for a time period longer than or equal to the predefined time period.

5. The method according to claim 4, wherein the predefined time period is at least 1 ms.

6. The method according to claim 1, wherein the detection of when at least one of the two or more gripping structures is in contact with the object is carried out by measuring a pressure (P) with which at least one of the two or more gripping structures presses against the object, wherein said pressure (P) is measured by a detection unit comprising one or more sensor members, wherein contact between the object and at least one of the two or more gripping structures is defined as occurring when the pressure (P) exceeds a predefined pressure level (P′).

7. The method according to claim 1 further comprising a step of initially letting the two or more gripping structures move without restricting their relative displacement with respect to each other as long as none of the gripping structures are in contact with the object.

8. The method according to claim 1 further comprising a step of controlling the magnitude of a pressure with which at least one of the two or more gripping structures presses against the object.

9. The method according to claim 1, further comprising a step of detecting at least one parameter indicative of a pressure or force with which at least one of the two or more gripping structures presses against the object.

10. The method according to claim 1 further comprising a step of measuring a current and/or a voltage and/or a force of an actuator arranged to drive at least one of the two or more gripping structures, wherein the contact with an object is defined on the basis of the measured current and/or voltage and/or force.

11. The method according to claim 1 further comprising a step of providing one or more sensors to detect the contact with the object.

12. A gripping device for a robot, said gripping device comprising: two or more gripping structures movably arranged relative to each other and configured to grip an object; a detection unit configured to detect when the object is in contact with at least one of the two or more gripping structures, one or more actuators configured to make at least one of the two or more gripping structures move to grip the object, a control unit configured to control the one or more actuators, wherein the control unit is configured to restrict displacement (ΔD) of at least one of the two or more gripping structures so that said displacement (ΔD) is less than or equal to a predefined maximum displacement (ΔD.sub.max), and wherein the gripping device is configured to increase a force (F) exerted by at least one of the two or more gripping structures to the object from a predefined first level (F.sub.1) to a predefined second level (F.sub.2) when the detection unit has detected that at least one of the two or more gripping structures is in contact with the object.

13. The gripping device according to claim 12, wherein a ratio between the predefined second level (F.sub.2) and the predefined first level (F.sub.1) is at least 2.0.

14. The gripping device according to claim 12, wherein the gripping device is configured to increase the force (F) from the predefined first level (F.sub.1) to the predefined second level (F.sub.2) linearly as a function of the displacement of at least one of the two or more gripping structures.

15. The gripping device according to claim 12, wherein the detection unit is configured to detect when at least one of the two or more gripping structures has been in contact with the object for a predefined time period, wherein the control unit is configured to only increasing the force (F) exerted by at least one of the two or more gripping structures to the object if at least one of the two or more gripping structures has been in contact with the object for a time period longer than or equal to the predefined time period.

16. The gripping device according to claim 12, wherein the gripping device is configured to initially let the two or more gripping structures move without restricting their relative displacement with respect to each other as long as none of the gripping structures are in contact with the object.

17. The gripping device according to claim 12, wherein the gripping device is configured to control a magnitude of a pressure with which at least one of the two or more gripping structures presses against the object.

18. The gripping device according to claim 12, wherein the gripping device is configured to measure a current and/or a voltage and/or a force of an actuator arranged to drive at least one of the two or more gripping structures, wherein the contact with the object is defined on the basis of the measured current and/or voltage and/or force.

19. The gripping device according to claim 18, wherein the detection unit is an integrated detection unit configured to detect when the object is in contact with at least one of the two or more gripping structures on the basis of measurements performed on one or more of the actuators and the control unit is configured to restrict the displacement (ΔD) of at least one of the two or more gripping structures when the integrated detection unit has detected that the object is in contact with at least one of the two or more gripping structures.

20. The gripping device according to claim 12, wherein the detection unit comprises one or more sensor members.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0146] The invention will become more fully understood from the detailed description given herein below. The accompanying drawings are given by way of illustration only, and thus, they are not limitative of the present invention. In the accompanying drawings:

[0147] FIG. 1A shows a side perspective view of a gripping device according to the invention in a first configuration;

[0148] FIG. 1B shows a perspective view of the gripping device shown in FIG. 1A in a second configuration;

[0149] FIG. 1C shows a close-up view of the gripping device shown in FIG. 1A and FIG. 1B in a third configuration;

[0150] FIG. 2 shows a close-up view of a gripping device according to the invention;

[0151] FIG. 3A shows a graph depicting the force exerted by the gripping device as a function of the displacement of the gripping structures relative to each other in an embodiment of the invention;

[0152] FIG. 3B shows a graph depicting the force exerted by the gripping device as a function of the displacement of the gripping structures relative to each other in another embodiment of the invention;

[0153] FIG. 4A shows a side view of a gripping structure of a gripping device according to the invention;

[0154] FIG. 4B shows a front-view of a pressure sensor;

[0155] FIG. 4C shows a graph depicting the pressure distribution along a line (row) of pressure sensing elements of the pressure sensor shown in FIG. 4B;

[0156] FIG. 5 shows a cross-sectional view of a gripping device according to the invention;

[0157] FIG. 6 shows a gripping device according to the invention being attached to a collaborative robot;

[0158] FIG. 7A shows a top view of a gripping device according to the invention, wherein the gripping device is operated in a mode in which the gripping structures are not in contact with the object to be handled, in which mode the gripping structures are moved without restricting their relative displacement with respect to each other;

[0159] FIG. 7B shows a top view of the gripping device shown in FIG. 7A, in a configuration in which there is contact between the object and the gripping structures;

[0160] FIG. 8A shows a top view of a gripping device according to the invention comprising two gripping structures each connected to a connection member that is rotatably attached to an actuator;

[0161] FIG. 8B shows a gripping device according to the invention configured to grip a tubular structure in a first configuration; and

[0162] FIG. 8C shows the gripping device shown in FIG. 8B in another configuration.

DETAILED DESCRIPTION

[0163] Referring now in detail to the drawings for the purpose of illustrating preferred embodiments of the present invention, a portion of a gripping device 2 of the present invention is illustrated in FIG. 1A. FIG. 1A illustrates a perspective view of a gripping device 2 according to the invention in a first configuration, in which a first gripping structure 4 and a second gripping structure 4′ of the gripping device 2 are moved toward each other in order to grip an object 8 arranged there between. The first gripping structure 4 is provided in the distal end of a first rod-shaped connection member 6. Likewise, the second gripping structure 4′ is provided in the distal end of a second rod-shaped connection member 6′.

[0164] The gripping device 2 comprises one or more actuators (not shown) configured to move the gripping structures 4, 4′ towards each other and away from each other by moving at least one of the connection members 6, 6′.

[0165] FIG. 1B illustrates a perspective view of a portion of the gripping device 2 shown in FIG. 1A in a second configuration, in which the gripping structures 4, 4′ have been moved further towards each other.

[0166] FIG. 1C illustrates a close-up view of the gripping device 2 shown in FIG. 1A and FIG. 1B in a third configuration, in which the first gripping structure 4 has been brought into contact with the object 8.

[0167] The contact triggers the control unit (not shown) of the gripping device 2 to restrict the displacement ΔD of the first gripping structure 4 relative to the second gripping structure 4′. Accordingly, the gripping device 2 is operated in a manner in which the displacement ΔD is less than or equal to a predefined maximum displacement, ΔD.sub.max. In an embodiment, the predefined maximum displacement, ΔD.sub.max is within the range 0.1-1.0 mm such as 0.2-0.5 mm.

[0168] The initial position (before the displacement of the first gripping structure 4 relative to the second gripping structure 4′) is indicated with a solid line, whereas the end position (when the first gripping structure 4 has been moved towards the second gripping structure 4′) is indicated with a dotted line.

[0169] FIG. 2 illustrates a close-up view of a portion of a gripping device 2 according to the invention. The gripping device 2 comprises two parallel connection members 6, 6′ that each carry a disc-shaped gripping structure 4, 4′ provided at the distal end. An object 8 is arranged between the first gripping structure 4 and the second gripping structure 4′.

[0170] A finger 16 of a human is arranged between the object 8 and the second gripping structure 4′. When the gripping device 2 detects that there is contact with the finger 16 and the second gripping structure 4′, this detected contact triggers the control unit (not shown) of the gripping device 2 to restrict the displacement of the first gripping structure 4 relative to the second gripping structure 4′.

[0171] Accordingly, the gripping device 2 is operated in a manner in which the distance D.sub.2 between the object and the second gripping structure 4′ is restricted. Accordingly, the gripping device 2 is configured to prevent the finger from being injured by the compressive force exerted to the finger by the gripping structures 4, 4′ or the object 8 and one of the gripping structures 4, 4′.

[0172] FIG. 3A illustrates a graph depicting the force F exerted by the gripping device as a function of the displacement D of the gripping structures relative to each other in an embodiment of the invention. In the initial phase I, the gripping structures are moved towards each other and the force F.sub.1 exerted by the gripping structures is very low (close to zero). When contact with an object is reached (in phase II) by either the first gripping structure or the second gripping structure, the force F.sub.2 exerted by the gripping structures (towards the object) is increased almost instantaneously to a high level (indicated with a dotted line). This high-level force F.sub.2 is sufficiently large to achieve a reaction force (normal force) required to provide a friction force of sufficient magnitude to maintain a firm grip of the object.

[0173] It can be seen that the displacement ΔD in the second phase II is limited. Thus, the gripping structures are restricted from injuring a finger or another part of a human that is brought into contact with one of the gripping structures.

[0174] FIG. 3B illustrates a graph depicting the force F exerted by the gripping device as a function of the displacement D of the gripping structures relative to each other in another embodiment of the invention. In the initial phase I the gripping structures are moved towards each other and the force F.sub.1 exerted by the gripping device is very low. However, when contact with an object is reached (in phase II) by either the first gripping structure or the second gripping structure, the force F.sub.2 exerted by the gripping device (towards the object) is ramped up to a high level (indicated with a dotted line).

[0175] As the displacement ΔD in the second phase II is limited (restricted), the gripping device is restricted from injuring a finger or another part of a human that is brought into contact with one of the gripping structures of the gripping device.

[0176] FIG. 4A illustrates a side view of a gripping structure 4 of a gripping device according to the invention. The gripping structure 4 comprises a gripping surface provided with a sensor comprising a plurality of sensor members 18, 18′, 18″ each configured to measure pressure.

[0177] FIG. 4B illustrates a front-view of a pressure sensor of the type that basically corresponds to the one shown in FIG. 4A. The pressure sensor, however, comprises more sensor members 18, 18′, 18″ each configured to measure pressure.

[0178] FIG. 4C illustrates a graph depicting the pressure P distribution along a line (row) of pressure sensing elements of the pressure sensor shown in FIG. 4B. It can be seen that in the central part of the graph, the pressure P exceeds a predefined upper pressure level P′. Accordingly, some of the pressure sensing sensor members detect a pressure that exceeds the predefined upper pressure level P′.

[0179] In an embodiment, contact is defined to occur when one or more of the pressure sensing sensor members detect a pressure that exceeds the predefined upper pressure level P′.

[0180] In another embodiment, contact is defined to occur when the average pressure detected by the pressure sensing sensor members exceeds the predefined upper pressure level P′.

[0181] In a further embodiment, contact is defined to occur when the average pressure detected by a predefined number (e.g. 10 or 20) of pressure sensing sensor members exceeds the predefined upper pressure level P′.

[0182] FIG. 5 illustrates a cross-sectional view of a gripping device 2 according to the invention. The gripping device 2 comprises a first gripping structure 4 that is rotatably attached to a first threaded rod 34. The gripping device 2 comprises a second gripping structure 4′ rotatably attached to a second threaded rod 34′.

[0183] A first actuator formed as an electric motor 32 is coupled to the first threaded rod 34 by means of a first rod-shaped connection structure 38. A second actuator formed as an electric motor 32′ is coupled to the second threaded rod 34′ by means of a second rod-shaped connection structure 38′. Each of the electric motors 32, 32′ are electrically connected to a control unit 42 by means of cables. In an alternative embodiment, the electric motors 32, 32′ may be wirelessly connected to the control unit 42 and electrically connected to a power supply (e.g. a battery).

[0184] The control unit 42 is electrically connected to sensor members 18 provided at a surface of the gripping structures 4, 4′. In an alternative embodiment, the sensor members 18 may be wirelessly connected to the control unit 42.

[0185] The gripping device 2 comprises a housing 40. The gripping structures 4, 4′ protrude from the housing 40 of the gripping device 2. A human finger 16 is arranged in the space between the gripping structures 4, 4′ in non-zero distances D.sub.1, D.sub.2 from each of the gripping structures 4, 4′, respectively. When the gripping structures 4, 4′ gradually are moved toward each other, the distances D.sub.1, D.sub.2 between the finger 16 and the griping structures 4, 4′ will gradually decrease until there is contact between the finger 16 and one of the gripping structures 4, 4′.

[0186] When the gripping device 2 detects that there is contact with the finger 16 and the second gripping structure 4′, this contact triggers the control unit 42 of the gripping device 2 to restrict the displacement of the first gripping structure 4 relative to the second gripping structure 4′. In practice, the control unit 42 may control the electric motors 32, 32′ in a first mode when no contact has been detected and in another mode when contact has been detected.

[0187] In an embodiment, the contact between the finger 16 and one of the gripping structures 4, 4′ is detected by using one or more sensor members 18.

[0188] In another embodiment, the contact between the finger 16 and one of the gripping structures 4, 4′ is detected on the basis of measurement(s) of the current and/or voltage and/or power of at least one of the electric motors 32, 32′.

[0189] The gripping device 2 is operated in a manner, in which the distance D.sub.1, D.sub.2 between the finger 16 and the gripping structures 4, 4′ is restricted, when contact is detected. Accordingly, the gripping device 2 is configured to prevent the finger 16 from being injured by the compressive force exerted to the finger by the gripping structures 4, 4′ or an object (not shown) and one of the gripping structures 4, 4′.

[0190] FIG. 6 illustrates a gripping device 2 according to the invention being attached to a collaborative robot 20. The robot 20 comprises a base 24 and a first arm 26 rotatably attached to said base 24. The robot 20 further comprises a second arm 26′ rotatably attached to the first arm 26. The robot 20 moreover comprises a third arm 26″ rotatably attached to the second arm 26′.

[0191] A first portion 28 is provided at the end of the third arm 26″. The first portion 28 is configured to receive a corresponding second portion 30 attached to the gripping device 2.

[0192] The robot 20 comprises a socket 21 configured to receive a corresponding plug 23 of the gripping device 2 in order to electrically connect the gripping device 2 and the robot 20. The plug 23 is attached at the distal end of a cable 22 connected to the gripping device 2.

[0193] The gripping device 2 comprises a body portion and a plurality of extremities 10, 10′ moveably attached to the body portion of the gripping device 2. The first extremity 10 is provided with a plurality of suction members 12 gripping a first object 58 by providing a negative pressure in the suction members 12.

[0194] The second extremity 10′ is provided with a plurality of suction members 12′ gripping a second object 60 by providing a negative pressure in the suction members 12′. The gripping device 2 comprises a centrally arranged support portion 14 provided with several suction members.

[0195] FIG. 7A illustrates a top view of a gripping device 2 according to the invention, wherein the gripping device 2 is operated in a non-contact mode (a mode in which the gripping structures 4, 4′, 4″ are not in contact with the object 8 to be handled). The gripping structures 4, 4′, 4″ are moved (by means of actuators which are not shown) towards the object 8 without restricting their relative displacement with respect to each other. The first gripping structure 4 is arranged at the distal end of a first connection member 6, the second gripping structure 4′ is arranged at the distal end of a second connection member 6′ and the third gripping structure 4″ is arranged at the distal end of a third connection member 6″.

[0196] The magnitude of the force F.sub.1 applied to the gripping members 4, 4′, 4″ for moving them towards the object 8 is indicated by arrows.

[0197] FIG. 7B illustrates a top view of the gripping device 2 shown in FIG. 7A, in a contact mode (a configuration in which contact has been detected between the object 8 and the gripping structures 4, 4′, 4″). Since contact has been detected between the object 8 and the gripping structures 4, 4′, 4″, the control unit (not shown) is operated in a mode in which the one or more actuators (not shown) arranged to move the gripping structures 4, 4′, 4″ will restrict the displacement of at least one of the gripping structures 4, 4′, 4″ towards the object 8 so that the displacement is less than or equal to a predefined maximum displacement. Hereby, it is possible to avoid damage of a human tissue (e.g. a finger of a human) arranged between the gripping structures 4, 4′, 4″. It can be seen that the magnitude of the force F.sub.2 applied to the gripping members 4, 4′, 4″ for pressing them towards the object 8 is indicated by arrows. When comparing FIG. 7A and FIG. 7B it can be seen that F.sub.2 is larger than F.sub.1. Thus, in the contact mode, the force F.sub.2 exerted by at least one of the gripping structures 4, 4′, 4″ to the object 8 is increased compared to the non-contact mode (shown in FIG. 7A).

[0198] FIG. 8A illustrates a top view of a gripping device 2 according to the invention comprising two gripping structures 4, 4′ each connected to a connection member 6, 6′ that is rotatably attached to an actuator 32, 32′. The first gripping structure 4 is attached to a first connection member 6 being rotatably attached to a first actuator 32. The second gripping structure 4′ is attached to a second connection member 6′ that is rotatably attached to a second actuator 32′. Accordingly, the first actuator 32 and the second actuator 32′ can be operated independently of each other. The arced movement pattern of the first gripping structure 4 and the second gripping structure 4′ is indicated with dashed lines.

[0199] The gripping structures 4, 4′ are brought into contact with an object 8. The gripping device 2 comprises a detection unit (not shown) configured to detect when the object 8 is in contact with at least one of the gripping structures 4, 4′.

[0200] The gripping device 2 comprises a control unit (not shown) configured to control the actuators 32, 32′ and to restrict the displacement of at least one of the gripping structures 4, 4′ towards the object 8 so that the displacement is less than or equal to a predefined maximum displacement. Hereby, damage of a human tissue (e.g. a finger of a human) arranged between the gripping structures 4, 4′ can be avoided.

[0201] The control unit is configured to increase the force exerted by at least one of the gripping structures 4, 4′ to the object 8 when the detection unit has detected that the at least one of the two or more gripping structures 4, 4′ is in contact with the object 8. Hereby, it is possible to increase the normal force and thus the friction force and thus provide a firm grip of the object 8. In an embodiment, the predefined maximum displacement may be 0.1-0.3 mm, such as 0.2 mm. In another embodiment, the predefined maximum displacement may be 0.4-0.6 mm such as 0.5 mm. In a further embodiment, the predefined maximum displacement may be 0.7-1.0 mm such as 0.8 mm.

[0202] FIG. 8B illustrates a top view of a gripping device 2 according to the invention comprising three gripping structures 4, 4′, 4″ each connected to a connection member 6, 6′, 6″ comprising a plurality of telescopic structures arranged to be translated with respect to each other. The gripping device 2 comprises a control unit (not shown) that is operated in a non-contact mode (in which there is no physical contact between the gripping structures 4, 4′, 4″ and the (inside surface of the) pipe-shaped object 8.

[0203] FIG. 8C illustrates the gripping device 2 shown in FIG. 8B in a configuration, in which a detection unit (not shown) of the gripping device 2 has detected contact between the object 8 and some of the gripping structures 4′, 4″. There is no contact between the last gripping structure 4 and the object 8. Accordingly, the control unit will regulate the one or more actuators (not shown) arranged to move the gripping structures 4, 4′, 4″ in such a manner that the displacement of the gripping structures 4′, 4″ being in contact with the object 8 is restricted (and thus kept below a predefined maximum allowable level).

[0204] In one embodiment, the control unit is configured to allow the gripping structure 4 to be moved towards the object 8 as long as no contact is detected between the gripping structure 4 and the object.

LIST OF REFERENCE NUMERALS

[0205] 2 Gripping device [0206] 4, 4′ Gripping structure [0207] 6, 6′ Connection member [0208] 8 Object [0209] 10, 10′ Extremity [0210] 12, 12 Suction member (e.g. suction disc) [0211] 14 Support portion [0212] 16 Body portion [0213] 18, 18′, 18″ Sensor member (e.g. a pressure sensor) [0214] 20 Robot [0215] 21 Socket [0216] 22 Cable [0217] 23 Plug [0218] 24 Base [0219] 26, 26′, 26″ Arm [0220] 28 Attachment structure [0221] 30 Attachment member [0222] 32 Actuator (e.g. electrical motor) [0223] 34 Threaded rod (worm shaft) [0224] 38 Connection structure [0225] 40 Housing [0226] 42 Control unit [0227] 58 Object [0228] 60 Object [0229] F, F.sub.1, F.sub.2 Force [0230] P, P′ Pressure [0231] D, D.sub.1, D.sub.2 Distance [0232] ΔD Displacement [0233] ΔD.sub.max Maximum displacement [0234] F, F.sub.1, F.sub.2 Force exerted by the gripping device [0235] I First phase [0236] II Second phase