Vibration control of free piston machines through frequency adjustment

Abstract

A method and apparatus for minimizing the amplitude of mechanical vibrations of a mechanical apparatus including a linear, freely reciprocating, prime mover coupled to and driving a reciprocating mass of a driven machine in reciprocation at a driving frequency. The coupled prime mover and driven machine have a spring applying a force upon the reciprocating mass to form a resonant main system having a main system resonant frequency of reciprocation. A driving frequency range over which the driven machine operates at an acceptable efficiency of operation is determined and stored. A parameter of the operation of the mechanical apparatus, such as the amplitude of vibrations or an operating temperature, is sensed and the prime mover is driven in response to the sensed parameter at a driving frequency that is offset from the main system resonant frequency of reciprocation, is within the driving frequency range of acceptable efficiency of operation and reduces or minimizes the amplitude of mechanical vibration of the mechanical apparatus under existing operating conditions.

1 . A method for minimizing the amplitude of mechanical vibrations of a mechanical apparatus including a linear, freely reciprocating, prime mover coupled to and driving a reciprocating mass of a driven machine in reciprocation at a driving frequency, the coupled prime mover and driven machine having a spring applying a force upon the reciprocating mass to form a resonant main system having a main system resonant frequency of reciprocation, the method comprising: 
 (a) determining and storing a driving frequency range over which the driven machine operates at an acceptable efficiency of operation;    (b) sensing a parameter of the operation of the mechanical apparatus; and    (c) driving the prime mover in response to the sensed parameter at a driving frequency that 
 (i) is offset from the main system resonant frequency of reciprocation;  
 (ii) is within the driving frequency range of acceptable efficiency of operation; and  
 (iii) reduces or minimizes the amplitude of mechanical vibration of the mechanical apparatus under existing operating conditions.  
   
   
   
       2 . A method in accordance with  claim 1  wherein the sensing step comprises sensing the amplitude of vibration of the mechanical apparatus and wherein the method further comprises: 
 (a) sweeping the driving frequency over a frequency range that includes the main system resonant frequency of reciprocation;    (b) storing the sensed amplitude of vibration in association with a plurality of the sweeping drive frequencies; and    wherein the prime mover is driven at a driving frequency that is a stored driving frequency associated with the smallest, sensed, stored amplitude.    
   
   
       3 . A method in accordance with  claim 2  wherein the method is periodically repeated.  
   
   
       4 . A method in accordance with  claim 1  for controlling a mechanical apparatus in which the driven machine is a free piston, Stirling, heat pumping apparatus, wherein 
 (a) the driving frequency range is determined and stored in response to testing of at least one component of said mechanical apparatus;    (b) at least one heat pumping apparatus of the mechanical apparatus is operated during a test at a plurality of operating temperatures, for each of the operating temperatures the driving frequency is varied within the acceptable driving frequency range and the driving frequency resulting in the least amplitude of vibration of the mechanical apparatus is stored in association with each operating temperature;    (c) the operating temperatures and associated driving frequencies are stored as a lookup table in a memory device connected in a frequency control system of replications of the tested mechanical apparatus;    (d) the sensing step comprises sensing the operating temperature of the replications of the tested mechanical apparatus; and    (e) the prime mover is driven at the stored driving frequency associated with the sensed temperature.    
   
   
       5 . A computer or logic circuit control system for minimizing the amplitude of mechanical vibrations of a mechanical apparatus including a main machine having a linear, freely reciprocating prime mover driving a driven machine in reciprocation, the main machine including a mass and springs applying a force upon the mass to provide a resonant mechanical oscillator having a resonant frequency near which the main machine is designed to be operatively driven, the control system comprising: 
 (a) a sensor for sensing a parameter of machine operation;    (b) a data storage for storing a driving frequency range over which the driven machine operates at an acceptable efficiency of operation; and    (c) a microcontroller connected to receive inputs from the sensor and the data storage for controlling the prime mover and programmed for driving the prime mover in response to the sensed parameter at a driving frequency that is offset from the main machine's resonant frequency of reciprocation, is within the stored driving frequency range of acceptable efficiency of operation and minimizes the amplitude of mechanical vibration of the mechanical apparatus under existing operating conditions.    
   
   
       6 . A control system according to  claim 5  wherein the sensor senses the amplitude of vibrations of the mechanical apparatus.  
   
   
       7 . A control system according to  claim 6  wherein the sensor is an accelerometer.  
   
   
       8 . A control system according to  claim 5  wherein the sensor is a temperature sensor.  
   
   
       9 . A control system in accordance with  claim 8  wherein the sensor is connected to sense the temperature of a spring of a vibration balancer.  
   
   
       10 . A control system in accordance with  claim 5  wherein the prime mover is a linear, electric motor.  
   
   
       11 . A control system in accordance with  claim 5  wherein the prime mover is a free piston Stirling engine.  
   
   
       12 . A control system in accordance with  claim 5  wherein the driven machine is a free piston Stirling cooler.