Pump end of stroke sensor

Abstract

A prime mover includes a shaft assembly that is supported for reciprocal movement between first and second ends of a stroke, and that includes first and second portions having a first material, and a third portion in between the first and second portions, having a second material, different from the first material. A single inductive proximity sensor makes a first indication when proximate the first material, and makes a second indication, when proximate the second material. A portion of the sensor is proximate the first portion when the shaft is at the first end of the stroke, the same portion of the same sensor is proximate the second portion when the shaft is at the second end of the stroke, and the same portion of the same sensor is proximate the third portion the entire time the shaft is in between the first and second ends of the stroke.

1 . A prime mover comprising:
 a shaft assembly supported for reciprocal movement between first and second ends of a stroke, the shaft assembly include first and second portions having a first material and a third portion in between the first and second portions having a second material different from the first material; and   a single inductive proximity sensor making a first indication in response to being proximate the first material and making a second indication different from the first indication in response to being proximate the second material;   wherein a portion of the single inductive proximity sensor is proximate the first portion of the shaft assembly when the shaft is at the first end of the stroke;   wherein the same portion of the same single inductive proximity sensor is proximate the second portion of the shaft assembly when the shaft is at the second end of the stroke; and   wherein the same portion of the same single inductive proximity sensor is proximate the third portion of the shaft assembly the entire time the shaft is in between the first and second ends of the stroke.   
   
   
       2 . The prime mover of  claim 1 , further comprising:
 a source of motive fluid;   an exhaust assembly;   first and second motive fluid chambers, the shaft moving to the first end of the stroke in response to the second motive fluid chamber being in communication with the source of motive fluid and the first motive fluid chamber being in communication with the exhaust assembly, and the shaft moving to the second end of the stroke in response to the first motive fluid chamber being in communication with the source of motive fluid and the second motive fluid chamber being in communication with the exhaust assembly;   a master valve in communication with the source of motive fluid and shiftable between a first condition in which the master valve places the source of motive fluid in communication with the second motive fluid chamber and places the first motive fluid chamber in communication with the exhaust assembly to cause shaft assembly movement to the first end of the stroke, and a second condition in which the master valve places the source of motive fluid in communication with the first motive fluid chamber and places the second motive fluid chamber in communication with the exhaust assembly to cause shaft assembly movement to the second end of the stroke; and   a controller communicating with the single inductive proximity sensor to receive the first and second indications, and communicating with the master valve to switch the master valve between the first and second conditions each time the controller receives the first indication from the single inductive proximity sensor.   
   
   
       3 . The prime mover of  claim 1 , wherein the first indication includes generation of a proximity signal; and wherein the second indication includes generation of no signal. 
   
   
       4 . The prime mover of  claim 1 , wherein the second indication includes generation of a proximity signal; and wherein the first indication includes generation of no signal. 
   
   
       5 . The prime mover of  claim 1 , wherein the first and second portions of the shaft assembly include notches to create an air gap between the single inductive proximity sensor and the shaft assembly; wherein the third portion of the shaft assembly includes a metallic material proximate the single inductive proximity sensor; wherein the first indication includes generation of no signal; and wherein the second indication includes generation of a proximity signal. 
   
   
       6 . The prime mover of  claim 1 , wherein the shaft assembly includes a shaft having a first outer diameter and a ring having a second outer diameter larger than the first outer diameter; wherein the ring is affixed to and covers a portion the shaft; wherein the ring is constructed of metallic material; wherein the third portion of the shaft assembly is defined by the ring and the portion of the shaft covered by the ring; wherein the first and second portions of the shaft assembly include portions of the shaft adjacent to opposite ends of the ring and not covered by the ring; wherein the metallic material of the ring in the third portion is proximate the single inductive proximity sensor when the shaft assembly is in between the first and second ends of the stroke; and wherein an air gap is interposed between the shaft and the single inductive proximity sensor when the shaft assembly is at the first and second ends of the stroke such that the single inductive proximity sensor is not proximate the shaft. 
   
   
       7 . The prime mover of  claim 1 , wherein the shaft assembly includes a shaft constructed of metallic material and a sleeve constructed of non metallic material covering a portion of the shaft; wherein the third portion of the shaft assembly is defined by the sleeve and the portion of the shaft covered by the sleeve; wherein the first and second portions of the shaft assembly include portions of the shaft adjacent to opposite ends of the sleeve and not covered by the sleeve; wherein the metallic material of the shaft in the first and second portions is proximate the single inductive proximity sensor when the shaft assembly is at the respective first and second ends of the stroke; and wherein the sleeve is interposed between the shaft and the single inductive proximity sensor when the shaft assembly is in between the first and second ends of the stroke. 
   
   
       8 . A method of operating a machine, the method comprising:
 providing a shaft assembly comprising first and second portions having a first material and a third portion having second material different from the first material;   providing a drive assembly operable to drive reciprocation of the shaft assembly between first and second opposite ends of a stroke;   providing a single inductive proximity sensor;   positioning the first portion of the shaft assembly proximate the single inductive proximity sensor when the shaft assembly is at the first end of the stroke;   positioning the second portion of the shaft assembly proximate the single inductive proximity sensor when the shaft assembly is at the second end of the stroke;   positioning the third portion of the shaft assembly proximate the single inductive proximity sensor the entire time the shaft assembly is in between the first and second ends of the stroke;   making a first indication with the single inductive proximity sensor in response to the single inductive proximity sensor being proximate the first and second portions of the shaft assembly;   making a second indication different from the first indication with the single inductive proximity sensor in response to the single inductive proximity sensor being proximate the third portion of the shaft assembly; and   actuating the drive assembly to reverse a direction of movement of the shaft assembly in response to the single inductive proximity sensor making the first indication.   
   
   
       9 . The method of  claim 8 , wherein making the first indication includes generating a proximity signal; and wherein making the second indication includes generating no signal. 
   
   
       10 . The method of  claim 8 , wherein making the second indication includes generating a proximity signal; and wherein making the first indication includes generating no signal. 
   
   
       11 . The method of  claim 8 , wherein providing a shaft assembly includes creating an air gap between the single inductive proximity sensor and the shaft assembly in the first and second portions, and including a metallic material proximate the single inductive proximity sensor in the third portion; wherein making the first indication includes generating no signal; and wherein making the second indication includes generating a proximity signal. 
   
   
       12 . The method of  claim 8 , wherein providing a shaft assembly includes providing a shaft having a first outer diameter and a metallic ring having a second outer diameter larger than the first outer diameter; wherein providing a shaft assembly further includes affixing the ring to a portion the shaft and covering the portion of the shaft with the ring to define the third portion of the shaft assembly by the ring and the portion of the shaft covered by the ring; wherein providing a shaft assembly further includes defining the first and second portions of the shaft assembly with portions of the shaft adjacent opposite ends of the ring and not covered by the ring; wherein positioning the third portion of the shaft assembly proximate the single inductive proximity sensor includes positioning the metallic material of the ring proximate the single inductive proximity sensor when the shaft assembly is in between the first and second ends of the stroke; and wherein positioning the first and second portions of the shaft proximate the single inductive proximity sensor includes interposing an air gap between the shaft and the single inductive proximity sensor when the shaft assembly is at the first and second ends of the stroke such that the single inductive proximity sensor is not proximate the shaft. 
   
   
       13 . The method of  claim 8 , wherein providing a shaft assembly includes providing a shaft constructed of metallic material and a sleeve constructed of non metallic material covering a portion of the shaft; wherein providing a shaft assembly further includes defining the third portion of the shaft assembly by the sleeve and the portion of the shaft covered by the sleeve; wherein providing a shaft assembly further includes defining the first and second portions of the shaft assembly with portions of the shaft adjacent to opposite ends of the sleeve and not covered by the sleeve; wherein the steps of positioning the first and second portions of the shaft assembly proximate the single inductive proximity sensor include positioning the metallic material of the shaft in the first and second portions proximate the single inductive proximity sensor when the shaft assembly is at the respective first and second ends of the stroke; and wherein the step of positioning the third portion of the shaft assembly proximate the single inductive proximity sensor includes interposing the sleeve between the shaft and the single inductive proximity sensor the entire time the shaft assembly is in between the first and second ends of the stroke.