Heliostat mechanical stop and method of finding heliostat home position

Abstract

A drive assembly for a heliostat and a method of determining the drive's home position are described. The drive assembly comprises at least one mechanical hard stop for impeding the motion of an output gear of at least one gear transmission driven by a motor. Each hard stop may be built into the housing of a gear transmission or may be made integral with an output gear. The method for determining the drive assembly's home position comprises the steps of iteratively actuating an output gear towards, and then away from, a hard stop feature while monitoring the input torque of the driving motor. When the motor input torque is registered to be higher than a predetermined trip torque, the stepper motor is commanded to stop and the home position of the drive assembly is determined.

We claim: 
     
         1 . A heliostat drive assembly comprising:
 a drive chassis;   a drive shaft connected to the drive chassis;   a reflector channel connected to the drive chassis;   a first gear transmission comprising a first output gear, wherein the first gear transmission is configured to rotate said drive shaft via the first output gear about a first axis;   a second gear transmission comprising a second output gear, wherein the second gear transmission is configured to rotate said reflector channel via the second output gear about a second axis;   a motor controller configured to actuate the first and second gear transmissions;   a first stop feature configured to cease the motion of the first output gear; and   a second stop feature configured to cease the motion of the second output gear.   
     
     
         2 . The heliostat drive assembly of  claim 2 , wherein the first and second stop features comprise mechanical stops. 
     
     
         3 . The heliostat drive assembly of  claim 2 , wherein the first and second stops comprises flat surfaces. 
     
     
         4 . The heliostat drive assembly of  claim 1 , wherein the first stop is made integral with the drive chassis. 
     
     
         5 . The heliostat drive assembly of  claim 2 , wherein the first output gear comprises at least one protrusion. 
     
     
         6 . The heliostat drive assembly of  claim 5 , wherein the first output gear has an annulus shape and comprises an inner ring and an outer ring, wherein the outer ring has a larger diameter than the inner ring and a gap is present between the inner ring and the outer ring. 
     
     
         7 . The heliostat drive assembly of  claim 6 , wherein said protrusions are formed on the inner ring or on the outer ring. 
     
     
         8 . The heliostat drive assembly of  claim 7 , wherein said protrusions are collinear with the center of the first output gear. 
     
     
         9 . The heliostat drive assembly of  claim 8 , wherein said protrusions have planar faces. 
     
     
         10 . The heliostat drive assembly of  claim 1 , wherein the second stop is made integral with the drive chassis. 
     
     
         11 . The heliostat drive assembly of  claim 1 , wherein the second output gear comprises a tooth region having an arc segment between 120 and 150 degrees. 
     
     
         12 . The heliostat drive assembly of  claim 2 , wherein the second output gear further comprises at least one planar surface that makes flush contact with the second stop. 
     
     
         13 . The heliostat drive assembly of  claim 1 , wherein the motor controller has local memory storage. 
     
     
         14 . A method of determining the home position of a heliostat drive assembly, which comprises the steps of:
 (a) utilizing a motor controller having local memory storage to actuate at least one motor to drive at least one gear transmission having an output gear, wherein the output gear is configured to rotate a drive assembly about an axis and wherein the output gear is actuated in the direction of a hard stop feature;   (b) measuring the input torque of the at least one motor with a torque sensor while simultaneously driving the at least one gear transmission with the motor;   (c) measuring the step position of the at least one motor with the motor controller while simultaneously driving the at least one gear transmission with the motor;   (d) commanding the motor to cease operation upon exhibiting a predetermined condition;   (e) recording the current motor step position to the memory of the motor controller; and   (f) defining the recorded motor position as the home stop position in the motor controller memory.   
     
     
         15 . The method of determining the home position of a heliostat drive assembly of  claim 14 , further comprising the steps of:
 (g) actuating the stepper motor to move the output gear away from the stop feature a predetermined number of steps;   (h) repeating steps (a) through (f); and   (i) repeating steps (g) and (h) a predetermined number of times.   
     
     
         16 . The method of determining the home position of a heliostat drive assembly of  claim 14 , wherein the predetermined condition of step (d) is the registering by the torque sensor of a higher input torque to the respective gear transmission than a predetermined trip torque.