Galvanometer unit

Abstract

A galvanometer unit comprises a limited-rotation motor with a load element such as a mirror attached to a shaft extending from the motor. In a servo loop that controls the angular position of the mirror, a position-sensor attached to the shaft provides position feedback information. The sensor includes a rotor which is positioned at the null point of the fundamental torsional resonance mode of the rotating system, thereby essentially eliminating feedback components resulting from the resonance. If the motor armature is supported for rotation on ball or roller bearings, the controller for the motor causes complete rotation of the armature from time to time, thereby distributing bearing wear around the bearing races and prolonging the useful life of the bearings.

What is claimed is:  
     
         1 . A galvanometer unit comprising: 
 A. a motor having a rotor comprising; 
 1. an armature, and  
 2. first and second shafts extending from said armature;  
   B. a load element affixed to the end of said first shaft remote from said armature;    C. a controller for causing the motor to reciprocally rotate the rotor, said controller including a servo system for controlling the angular position of the load element, said servo system including a position sensor for sensing the angular position of the shaft, the position sensor including; 
 1. a sensor rotor attached to the shaft for rotation therewith, and  
 2. a stator assembly for sensing the angular position of the sensor rotor; the sensor rotor being positioned at the null point of the fundamental torsional resonance of the rotating system that includes the motor rotor, the shafts and the load element.  
   
     
     
         2 . The galvanometer unit defined in  claim 1  including means for adjusting the position of the null point to coincide with the position of the sensor rotor on the shaft.  
     
     
         3 . The galvanometer unit defined in  claim 1:   A. in which the stator assembly comprises first and second stators disposed around said shaft, said stators having opposing faces and opposing electrodes on said faces;    B. in which the rotor is; 
 1. of a dialetric material;  
 2. is affixed to said shaft between said opposing faces; and  
 3. has radially extending blades; and  
   C. including means for sensing the capacitances between said electrodes.    
     
     
         4 . The galvanometer unit defined in  claim 3:   A. including means for clamping said stators together.    B. including a cavity between the opposing electrodes; and    C. in which said rotor is disposed in said cavity.    
     
     
         5 . The galvanometer defined in  claim 1:   A. including first and second bearings supporting the rotor for rotation, each of the bearings having an inner race and an outer race; and    B. in which the controller includes means for providing full rotation of the armature at predetermined times, thereby to distribute wear on said bearings.    
     
     
         6 . A galvanometer unit comprising: 
 A. a motor, said motor having a rotor comprising an armature and shafts extending therefrom;    B. bearings supporting said armature for rotation, said bearings having inner races and outer races;    C. a load element supported from an end of one of said shafts remote from said armature for rotation therewith;    D. a controller for reciprocally rotating said rotor, said controller including a servo system for controlling the angular position of the load element; and    E. means in said controller for providing full rotation of said armature at commanded times, thereby to distribute wear on said bearings.    
     
     
         7 . The galvanometer unit defined in  claim 6  including a rotation stop unit for mechanically limiting the rotation of said rotor, said stop unit including 
 A. a stop pin projecting radially from one of said shafts;  
 B. a plurality of stop positioned to interfere with said stop pin and thereby limit rotation of said rotor; and  
 C. means for 
 1. retracting said stops, thereby permitting unlimited rotation of said rotor, and  
 2. repositioning said stops for engagement by said stop pin, thereby limiting the rotation of said rotor.  
 
 
     
     
         8 . A galvanometer unit comprising, a stator and a rotor, 
 A. said stator including field windings,    B. said rotor comprising an armature including a non-conducting permanent magnet providing a flux that interacts with fields generated by currents in said windings to provide rotation of the rotor,    C. said rotor further including 
 1. shafts abutting the ends of the armature, and  
 2. an electrically conducting sleeve enclosing said armature and the portions of said shafts adjacent to said armature, said sleeve being in electrical contact with said shafts and retaining said shafts, whereby said armature and said shafts rotate together as a single member.  
   
     
     
         9 . A galvanometer unit comprising 
 A. a limited-rotation motor;    B. a load reciprocally rotated by said motor;    C. cooling unit for removing heat from said motor, said cooling unit comprising 
 1. a heat-transfer surface of said motor,  
 2. a heat-dissipation plate having a first surface in intimate thermal contact with said motor surface, and a second surface having fins projecting therefrom, and  
 3. a fan projecting air toward said second surface, perpendicularly to said second surface, whereby air from said fan impinges on said second surface and flows outwardly therefrom along said fins.  
   
     
     
         10 . The galvanometer unit of  claim 1  including a cooling unit for removing heat from said motor, said cooling unit comprising 
 A. a heat-transfer surface of said motor,  
 B. a heat-dissipation plate having a first surface in intimate thermal contact with said motor surface, and a second surface having fins projecting therefrom, and  
 C. a fan projecting air toward said second surface, perpendicularly to said second surface, whereby air from said fan impinges on said second surface and flows outwardly therefrom along said fins.