Method and means for increasing the stiffness of limited frequency servo systems

In a damped second-order electromechanical servo system including a physical subsystem having a predetermined inertia, said subsystem being maintained in a commanded position by a command torque governed by signals applied to a driving means, and displaced from that position by a disturbance torque, said servo system including position and displacement velocity feedback means which produce position and velocity feedback signals which are applied to said driving means, the improvement comprising:

• (a) acceleration feedback means arranged to produce an acceleration feedback signal for application to said driving means, said acceleration feedback signal being proportional to the acceleration component of the displacement movement of said subsystem;
• and the effective gain of said acceleration feedback means being ##EQU3## where J is the inertia of said physical subsystem;
• K.sub.D is the effective gain of said driving means;
• K.sub.Do is the value of K.sub.D at which said servo system has desired values of damping and natural frequency in the absence of said acceleration feedback means;
• and X is the factor by which K.sub.D must be increased over K.sub.Do in order to obtain a desired stiffness factor of said servo system without changing the effective response time of said position feedback means, whereby said stiffness factor is decreased by a factor of X without changing the damping factor or natural frequency of said servo system;
• and
• (b) means for applying said acceleration feedback signal to said driving means.