Systems and methods of controlling instruments

A method comprising:

• determining, by a control unit of a computer-assisted device, a first position of a first actuator configured to actuate a degree of freedom of an instrument in a first direction using a first force or torque transmission mechanism;
• determining, by the control unit, a second position of a second actuator configured to actuate the degree of freedom in a second direction using a second force or torque transmission mechanism, the second direction being at least partially opposite to the first direction;
• determining, by the control unit, a force or torque command based on the first position, the second position, and a desired state of the degree of freedom;
• determining, by the control unit, a first actuation level of the first actuator and a second actuation level of the second actuator so as to maintain a first tension in the first force or torque transmission mechanism above a first minimum tension and maintain a second tension in the second force or torque transmission mechanism above a second minimum tension by:
• using a model based on the force or torque command, the first and second minimum tensions, the first position, and the second position;
• and
• commanding, by the control unit, actuation of the first actuator at the first actuation level and actuation of the second actuator at the second actuation level;
• wherein the model compensates for an external disturbance on the degree of freedom and for dynamics of the first actuator and the second actuator.

A non-transitory machine-readable medium comprising a plurality of machine-readable instructions which when executed by one or more processors associated with a computer-assisted medical device are adapted to cause the one or more processors to perform a method comprising:

• determining a first position of a first actuator configured to actuate a degree of freedom of an instrument in a first direction using a first force or torque transmission mechanism;
• determining a second position of a second actuator configured to actuate the degree of freedom in a second direction using a second force or torque transmission mechanism, the second direction being at least partially opposite to the first direction;
• determining a force or torque command based on the first position, the second position, and a desired state of the degree of freedom;
• determining a first actuation level of the first actuator and a second actuation level of the second actuator so as to maintain a first tension in the first force or torque transmission mechanism above a first minimum tension and maintain a second tension in the second force or torque transmission mechanism above a second minimum tension by:
• using a model based on the force or torque command, the first and second minimum tensions, the first position, and the second position;
• and
• commanding actuation of the first actuator at the first actuation level and actuation of the second actuator at the second actuation level;
• wherein the model compensates for an external disturbance on the degree of freedom and for dynamics of the first actuator and the second actuator.