US 5,032,772 A · Motor driver circuit for resonant linear cooler

Abstract

A direct current powered, linear resonant cryocooler having a compressor in which the piston is reciprocated by a linear motor at substantially resonant frequency and the length of stroke of the piston is varied as a direct function of cryocooler temperature. There are two control loops, a temperature control loop and a voltage control loop which is independent of the temperature control loop. In the temperature control loop, temperature is sensed at the cryocooler or expander and the temperature signal is compared with a reference temperature signal to produce a temperature error signal or voltage. The voltage control loop controls motor voltage. As input to the voltage control loop, the linear motor voltage is fed back and compared with the temperature error voltage V.sub.TE to produce a voltage level signal V.sub.L in the input of the voltage control loop, representative of the correction required to obtain and then to maintain the cryocooler temperature represented by the reference temperature voltage. Either a pulse width modulated, variable amplitude sine wave signal or a constant duty cycle, pulse width modulated, square wave signal powers the linear motor.

Claims14

Dependent claims

A direct current powered control system for controlling the length of the stroke of a piston of a linear motor compressor for a cryocooler, said motor having an armature member and a stator member, which are magnetically coupled, one of said members comprising a permanent magnet and the other of said members comprising a coil adapted to be reversibly energized, said direct current control system comprising:

a voltage control circuit having a cyclic, pulse width modulated electrical output of a frequency substantially the same as the resonant frequency of the linear motor compressor;
means for reversibly commutating said electrical output across said coil, synchronously with each half cycle of said electrical output;
means for producing a temperature error voltage;
means for producing a feedback voltage proportional to the voltage across said coil;
and
means for coupling the difference of said temperature error voltage and said feedback voltage as input to said voltage control circuit for controlling the power of each half cycle of said electrical output for controlling the length of the stroke of said piston.

3 more elements

a voltage control circuit comprising a pulse width modulator for producing a cyclic, pulse width modulated electrical output of substantially constant frequency connected to said coil;
means for sensing the temperature of said cryocooler and producing a temperature error voltage;
means for sensing the voltage of said coil and producing a feedback voltage which is approximately indicative of the length of the stroke of said piston;
means responsive to the difference between said temperature error voltage and said feedback voltage for producing a control voltage substantially indicative of a required length of piston stroke;
means for coupling said control voltage as input to said pulse width modulator to change the power of said cyclic electrical output to control the length of stroke of said piston;
and
means for reversibly coupling said cyclic electrical output to said coil, synchronously with each half cycle of said cyclic electrical output to reciprocate said piston.

4 more elements

Dependencies are inferred from the claim text.

Motor driver circuit for resonant linear cooler

Life of this patent

Motor driver circuit for resonant linear cooler

Life of this patent

Abstract

Claims14