Robotic joint control

A computer-implemented method of controlling a robotic system, the robotic system comprising a robot having a base and an arm extending from the base to an attachment for an instrument, the arm comprising n joints, where n>1, whereby the configuration of the arm can be altered, the arm having a plurality of configurations for a given relationship between the base and the attachment for the instrument, the robot comprising a driver for each joint configured to drive the joint to move and a joint sensor for each joint for sensing a state of the joint;

• the method comprising:
• obtaining a desired position of the attachment for the instrument;
• for each of k joints where k<n, obtaining a sensed joint state;
• comparing the obtained k sensed joint states to a set of constraint criteria, the set of constraint criteria being indicative of the arm moving from a first configuration towards a second configuration, where movement of the arm is more constrained in the second configuration than in the first configuration;
• where the obtained k sensed joint states match the set of constraint criteria, determining a magnitude of an adjustment signal configured to slow, halt or reverse movement of the arm towards the second configuration;
• using the desired position of the attachment for the instrument and the obtained k sensed joint states, determining a direction of the adjustment signal;
• gating the adjustment signal in dependence on movement of the attachment for the instrument by modifying the adjustment signal with a gating gain derived from a speed associated with the arm;
• for each of the n joints, obtaining a sensed joint state;
• using the desired position of the attachment for the instrument, the obtained n sensed joint states and the adjustment signal, determining a set of control signals for controlling the drivers;
• and
• driving the joints using the set of control signals.

A non-transitory computer readable storage medium having stored thereon computer readable instructions that, when executed at a computer system, cause the computer system to perform a method of controlling a robotic system, the robotic system comprising a robot having a base and an arm extending from the base to an attachment for an instrument, the arm comprising n joints, where n>1, whereby the configuration of the arm can be altered, the arm having a plurality of configurations for a given relationship between the base and the attachment for the instrument, the robot comprising a driver for each joint configured to drive the joint to move and a joint sensor for each joint for sensing a state of the joint;

• the method comprising:
• obtaining a desired position of the attachment for the instrument;
• for each of k joints where k<n, obtaining a sensed joint state;
• comparing the obtained k sensed joint states to a set of constraint criteria, the set of constraint criteria being indicative of the arm moving from a first configuration towards a second configuration, where movement of the arm is more constrained in the second configuration than in the first configuration;
• where the obtained k sensed joint states match the set of constraint criteria, determining a magnitude of an adjustment signal configured to slow, halt or reverse movement of the arm towards the second configuration;
• using the desired position of the attachment for the instrument and the obtained k sensed joint states, determining a direction of the adjustment signal;
• gating the adjustment signal in dependence on movement of the attachment for the instrument by modifying the adjustment signal with a gating gain derived from a speed associated with the arm;
• for each of the n joints, obtaining a sensed joint state;
• using the desired position of the attachment for the instrument, the obtained n sensed joint states and the adjustment signal, determining a set of control signals for controlling the drivers;
• and
• driving the joints using the set of control signals.