Method for generating a control output for a position control loop

Abstract

A method for optically detecting the position of a moveable test object ( 10 ), especially a mirror or reflector, in which a measuring beam ( 6 ) produced by a light source ( 2 ) is reflected by the test object ( 10 and reaches a position-sensitive light detector ( 12 ) which carrier out a conversion into information corresponding to the position of the test object ( 10 ). The invention enables the position of mirrors, especially rotating mirrors, to be quickly measured optically using a simple optical construction. The measuring beam ( 6 ) is focussed onto the light detector ( 12 ) by an optical system ( 8 ). A signal corresponding to the geometric center or the maximum (I 0 ) of the intensity distribution of the focussed measuring spot is determined based on the measured values obtained by the light detector ( 12 ).

1 . A method for generating a control output for a position control loop of a movable test object, said method comprising the steps of: 
 optically measuring the position of the test object by focussing a measuring beam generated by a light source onto the test object using an optical system, and reflecting the measuring beam from the test object as a focussed spot onto a position-sensitive light detector to obtain measured position information;    reading the measured position information obtained from the light detector serially into an analog to digital converter to obtain digitized position data;    transmitting the digitized position data a digital signal processor;    interpolating the digitized position data in said digital signal processor taking into account a distribution function corresponding to the actual intensity distribution to give a position signal corresponding to the geometric center or the maximum (I 0 ) of the intensity distribution of the focused measuring spot;    calculating a desired position of the test object with a system control computer;    supplying the calculated desired position to the signal processor;    generating a digital control value by comparing the position signal of the focussed measuring spot determined by interpolation with the calculated desired position;    generating an analog control value from the digital control value in a digital to analog converter, and    inputting the analog control value into a control loop for regulating the position of the test object.    
   
   
       2 . A method according to  claim 1 , wherein said movable test object is a mirror or reflector.  
   
   
       3 . A method according to  claim 1 , wherein a known distribution function of intensity (I) is taken into account when the geometric center or the maximum (I 0 ) is determined.  
   
   
       4 . A method according to  claim 1 , wherein lower intensity values are suppressed by a predefined threshold value (I S ) when the geometric center or the maximum (I 0 ) is determined.  
   
   
       5 . A method according to  claim 4 , wherein the threshold value (I S ) is between 20% and 50% of the maximum intensity (I 0 ).  
   
   
       6 . A method according to  claim 5 , wherein the threshold value (I S ) is on the order of magnitude of 30% of the maximum intensity (I 0 ).  
   
   
       7 . A method according to  claim 2 , wherein a control output signal is generated for direct control of the mirror position.  
   
   
       8 . A method according to  claim 1 , wherein said method is used in a scanning device, and the test object is a scanning mirror which carries out the scanning process using an additional light source.  
   
   
       9 . A method according to  claim 1 , wherein the corresponding distribution function is determined while the test object is stationary, and the distribution function is input into the signal processor.  
   
   
       10 . A method according to  claim 1 , wherein the corresponding distribution function is stored in a memory of the signal processor.  
   
   
       11 . An apparatus for generating a control output for a position control loop of a movable test object, said apparatus comprising: 
 a position sensitive light detector;    an analog to digital converter connected to receive measured position information from said light detector;    a signal processor connected to receive digital position data from said analog to digital converter, said signal processor comprising a memory for storing a distribution function, and    a digital to analog converter connected to receive a digital signal from said signal processor and generate an analog position regulating signal therefrom.    
   
   
       12 . An apparatus according to  claim 11 , further comprising a system control computer for calculating a desired object position, said signal processor being connected to said system control computer to receive a desired object position signal from the system control computer, and said signal processor being programmed to effect a comparison of the desired object position signal to a position signal derived from digitized position data received from the analog to digital converter.  
   
   
       13 . An apparatus according to  claim 12 , wherein the signal processor is programmed to generate a position control instruction to offset any deviation detected in the comparison of the desired object position signal to the position signal derived from the digitized position data.  
   
   
       14 . An apparatus according to  claim 11 , wherein said signal processor is programmed to determine a maximum intensity or a center of intensity distribution of a focussed light spot received by the position sensitive light detector from digitized position data received from the analog to digital converter.  
   
   
       15 . An apparatus according to  claim 11 , further comprising an object position control circuit connected to said digital to analog converter for regulating the position of a moveable object in response to an analog position regulating signal received from said digital to analog converter.