Servosystem for analogue plotters

Claim 1

An improved analogue recorder servosystem for positioning marking means relative to a recording medium in accordance with input signals indicative of a desired position comprising: input signal conditioning means for providing an input signal level having a full scale range in the order of several volts; servomotor means responsive to an applied error signal for causing relative movement of Said marking member in a selected coordinate direction relative to said recording medium; means for comparing said amplified input level with a feedback signal to generate an error signal for driving said servomotor toward the indicated position; output means including a followup potentiometer with a tap coupled to be moved by said servomotor for generating an output voltage indicative of the instantaneous position of said marking means; and feedback network means including a phase lead network and first operational amplifier means having opposite polarity inputs with a high input impedance, said output voltage being coupled to one of said opposite polarity inputs through said phase lead network, a reference voltage source for establishing a fixed operating potential across said output potentiometer, and a zero reference potentiometer coupled across said reference source and having a movable tap for selectively establishing a preselected zero reference voltage for positioning said marking means on said recording medium in the absence of an input signal, the movable tap on said zero reference potentiometer being coupled to the other of said inputs of said operational amplifier means to provide a feedback signal equal to the difference between said zero reference voltage and a voltage produced by applying said output voltage through said phase lead network for developing a feedback voltage to be compared by said comparing means with said amplified input level to generate said error signal.