Bilateral servosystem

Claim 1

A bilateral servosystem comprising a master member having an axis aligned coaxial with a predetermined axis, an electromechanical transducer mechanically coupled to said master member to produce an electrical output in accordance with the change in orientation of the axis of said master in relation to said predetermined axis, a slave member having another axis aligned coaxial with another predetermined axis corresponding to said one predetermined axis, another electromechanical transducer mechanically coupled to said slave member to produce an electrical output in accordance with the change in orientation of the axis of said slave member in relation to said other predetermined axis, the outputs from said slave transducer being matched to the outputs of said master transducer such that an output from said master transducer corresponding to a predetermined displacement of the axis of said master member from said one predetermined axis is equal to the output from said slave transducer corresponding to the same predetermined displacement of the axis of the slave member from said other predetermined axis, a slave servo loop including an electrical amplifier, a servo flow control valve and a slave actuator responsive to a difference in outputs of said transducers for maintaining said slave member axis in alignment with said master member axis, a master servo loop including said electrical amplifier, said servo flow control valve and a master actuator connected between the output of said valve and said master member in a polarity to oppose the movement of said master member which causes movement of said slave member, the inertia of said slave member being substantially greater than the inertia of said master member, the phase margin of said servo loop being positive at the frequency at which open loop gain is unity, the gain at frequencies below said frequency being sufficiently high to provide small compliance error, the open loop gain of said master servo loop being substantially higher than open loop gain of said slave servo loop, means for stabilizing said master loop including in circuit between said master member and said master transducer a network which introduces phase lag in the signal over a low frequency range and which introduces phase lead in the signal over a higher frequency range whereby the phase margin of said master loop at the frequency of crossover of the gain versus frequency characteristic of the master loop at unity gain is positive, and means for minimizing slew error of the system including a network in the slave loop in circuit between said slave member and said slave transducer having at least a lag time constant and a lead time constant which introduces a phase lag and a phase lead in the signal over a low-frequency range, said phase lag time constant being greater than said phase lead time constant of said network, each of said time constants being greater than the reciprocal of the frequency at unity open loop gain of the slave loop.