| CPC A61B 34/30 (2016.02) [A61B 90/06 (2016.02); A61B 2034/305 (2016.02); A61B 2090/064 (2016.02)] | 21 Claims |

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1. A computer-assisted device comprising:
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;
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; and
a control unit coupled to the first actuator and the second actuator;
wherein the control unit is configured to:
determine a first position of the first actuator;
determine a second position of the second actuator;
determine a force or torque command based on the first position, the second position, and a desired state of the degree of freedom;
determine 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
command 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.
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