System and method for breakaway clutching in an articulated arm
A system and method of breakaway clutching in a device includes a plurality of links coupled by a plurality of joints, a brake coupled to brake a first joint of the plurality of joints, and a control unit operatively coupled to the brake. The control unit includes one or more processors. The control unit switches the first joint from a first state of the first joint to a second state of the first joint in response to a determination that an external stimulus applied to the plurality of links or the plurality of joints meets at least a first criterion and switches the first joint from the second state to the first state in response to a speed associated with the first joint meeting at least a second criterion. The control unit causes more braking with the first brake in the first state than in the second state.
1. A device comprising:
a plurality of links coupled by a plurality of joints;
a brake coupled to brake a first joint of the plurality of joints; and
a control unit operatively coupled to the brake, the control unit comprising one or more processors;
wherein the control unit:
switches the first joint from a first state of the first joint to a second state of the first joint in response to a determination that an external stimulus applied to the plurality of links or the plurality of joints meets at least a first criterion, wherein the control unit causes more braking with the first brake in the first state than in the second state; and
switches the first joint from the second state to the first state in response to a speed associated with the first joint meeting at least a second criterion.
2. The device of claim 1 , wherein movement of the first joint is more restricted in the first state than in the second state due at least in part to the more braking with the first brake in the first state than in the second state.
3. The device of claim 1 , wherein:
the device comprises an arm, the arm comprising the plurality of links coupled by the plurality of joints;
the device further comprises a sensor; and
the control unit further determines whether the external stimulus meets the first criterion based on at least a value determined from information received from the sensor, the value being selected from the group consisting of:
a position error in a joint of the plurality of joints;
a force applied to a joint of the plurality of joints; and
a torque applied to a joint of the plurality of joints.
4. The device of claim 1 , wherein to cause more braking with the first brake in the first state than in the second state comprises, the control unit:
activates the first brake while the first joint is in the first state; and
at least partially releases the first brake while the first joint is in the second state.
5. The device of claim 1 , wherein the first criterion comprises:
the external stimulus exceeding a stimulus threshold; or
the external stimulus exceeding the stimulus threshold continuously for a predetermined period of time.
6. The device of claim 1 , wherein the second criterion comprises:
the speed associated with the first joint falling below a speed threshold; or
an aggregate of the speed associated with the first joint over a predetermined period of time is below the speed threshold; or
the speed associated with the first joint remaining below the speed threshold continuously for the predetermined period of time.
7. The device of claim 1 , wherein the control unit further:
delays switching, for a predetermined period of time after the determination has been made, of the first joint from the first state to the second state.
8. The device of claim 1 , wherein:
the device comprises an arm, the arm comprising the plurality of links coupled by the plurality of joints; and
the first criterion is based on one or more properties selected from the group consisting of:
a location of the first joint in the arm;
a location of a second joint in the arm;
an amount of error in a joint sensor associated with the first joint;
an amount of error in a joint sensor associated with a second joint;
whether the first joint is beyond a soft stop position near an end of possible motion for the first joint;
whether the second joint is beyond a soft stop position near an end of possible motion for the second joint;
whether the first joint is actuated or non-actuated;
whether the first joint is prismatic or rotational;
whether the second joint is actuated or non-actuated; and
whether the second joint is prismatic or rotational.
9. The device of claim 1 , wherein:
the device comprises an arm, the arm comprising the plurality of links coupled by the plurality of joints; and
the second criterion is based on one or more properties selected from the group consisting of:
a location of the first joint in the arm;
an amount of error in a joint sensor associated with the first joint;
whether the first joint is beyond a soft stop position near an end of possible motion for the first joint; and
whether the first joint is prismatic or rotational.
10. The device of claim 1 , wherein the control unit further controls, while the first joint is in the second state, the first joint to move to a commanded position based on a current actual position of the first joint, or the first joint to move with a commanded velocity based on a current actual velocity of the first joint.
11. The device of claim 1 , wherein the control unit further:
prevents the switching of the first joint from the first state to the second state when the device is in a predetermined mode selected from the group consisting of: a transport mode, a teleoperation mode, a commanded motion mode, and a docked to a patient mode.
12. A method of controlling a device comprising a plurality of links coupled by a plurality of joints and a brake coupled to brake a first joint of the plurality of joints, the method comprising:
switching, using a control unit, the first joint from a first state of the first joint to a second state of the first joint in response to determining that an external stimulus applied to the plurality of links or the plurality of joints meets at least a first criterion, wherein there is more braking with the first brake in the first state than in second first state; and
switching, using the control unit, the first joint from the second state to the first state in response to a speed associated with the first joint meeting at least a second criterion.
13. The method of claim 12 , wherein movement of the first joint is more restricted in the first state than in the second state due at least in part to the more braking with the first brake in the first state than in the second state.
14. The method of claim 12 , further comprising:
receiving, by the control unit, information about the plurality of joints or the plurality of links;
wherein determining whether the external stimulus meets the first criterion comprises determining a value based on the received information, the value being selected from the group consisting of:
a position error in one of the plurality of joints;
a force applied to one of the plurality of joints; and
a torque applied to one of the plurality of joints.
15. The method of claim 12 , wherein the first criterion comprises:
the external stimulus exceeding a stimulus threshold, or the external stimulus exceeding the stimulus threshold continuously for a predetermined period of time.
16. The method of claim 12 , wherein the second criterion comprises:
the speed associated with the first joint falling below a speed threshold; or
an aggregate of the speed associated with the first joint over a predetermined period of time is below the speed threshold; or
the speed associated with the first joint remaining below the speed threshold continuously for the predetermined period of time.
17. The method of claim 12 , further comprising:
delaying switching, for a predetermined period of time after the determination has been made, of the first joint from the first state to the second state.
18. A non-transitory machine-readable medium comprising a plurality of machine-readable instructions which, when executed by one or more processors associated with a device comprising a plurality of links coupled by a plurality of joints and a brake coupled to brake a first joint of the plurality of joints, are adapted to cause the one or more processors to perform a method comprising:
switching the first joint from a first state of the first joint to a second state of the first joint in response to determining that an external stimulus applied to the plurality of links or the plurality of joints meets at least a first criterion, wherein there is more braking with the first brake in the first state than in the second state; and
switching the first joint from the second state to the first state in response to a speed associated with the first joint meeting at least a second criterion.
19. The non-transitory machine-readable medium of claim 18 , wherein the method further comprises:
receiving information about the plurality of joints or the plurality of links;
wherein determining whether the external stimulus meets the first criterion comprises determining a value based on the received information, the value being selected from the group consisting of:
a position error in one of the plurality of joints;
a force applied to one of the plurality of joints; and
a torque applied to one of the plurality of joints.
20. The non-transitory machine-readable medium of claim 18 , wherein:
the first criterion comprises: the external stimulus exceeding a stimulus threshold, or the external stimulus exceeding the stimulus threshold continuously for a predetermined period of time; or
the second criterion comprises: the speed associated with the first joint falling below a speed threshold, or an aggregate of the speed associated with the first joint over a predetermined period of time is below the speed threshold, or the speed associated with the first joint remaining below the speed threshold continuously for the predetermined period of time.