Hydraulic cylinder position sensing and locking system and corresponding method

Abstract

The invention provides for a hydraulic cylinder position sensing and locking system that automatically maintains the position of a lock nut ( 36 ) that engages a plunger ( 16 ) on a hydraulic actuator such that if hydraulic pressure is lost, the lock nut prevents retraction of the plunger into the hydraulic cylinder ( 14 ). The hydraulic cylinder position sensing and locking system also provides for a position sensing feature that allows for the calculation of the axial stroke position of the plunger based on rotary movement of the lock nut. In addition, the invention provides for a synchronous hydraulic cylinder position sensing and locking system and methods of using both the hydraulic cylinder position sensing and locking system as well as the synchronous hydraulic cylinder position sensing and locking system.

What is claimed is: 
     
         1 . A hydraulic cylinder position sensing and locking system for a hydraulic actuator that includes a hydraulic cylinder, a plunger including a piston in the hydraulic cylinder and a threaded rod that extends axially from the piston so as to move with the piston, the plunger being axially moveable relative to the hydraulic cylinder in an extension direction and a retraction direction by selective supply of hydraulic fluid under pressure to the hydraulic cylinder, and including a lock nut that rotatably engages the threaded rod, the hydraulic cylinder position sensing and locking system comprising:
 a distance sensor that outputs a distance signal indicative of the axial spacing of the lock nut relative to the hydraulic cylinder;   a drive unit that can be operated to rotate the lock nut relative to the plunger; and   a controller that receives as an input the distance signal and outputs a control signal to control the drive unit so as to turn the lock nut in correspondence with axial movement of the plunger so as to maintain the spacing of the lock nut relative to the hydraulic cylinder within a desired range.   
     
     
         2 . The hydraulic cylinder position sensing and locking system of  claim 1 , further comprising a rotary position sensor that provides a signal indicative of rotary position of the drive unit, an axial position of the plunger determined at least in part based on the rotary position sensor signal. 
     
     
         3 . The hydraulic cylinder position sensing and locking system of  claim 2 , wherein the system determines the axial position of the plunger at least in part from the distance sensor signal. 
     
     
         4 . The hydraulic cylinder position sensing and locking system of  claim 1 , wherein the system determines the axial position of the plunger at least in part from the distance sensor signal. 
     
     
         5 . The hydraulic cylinder position sensing and locking system of  claim 1 , wherein there is at least an additional hydraulic actuator and corresponding lock nut, drive unit, and distance sensor as claimed in  claim 1 , and wherein each hydraulic actuator, drive unit, and distance sensor is connected to the controller and the controller determines the axial position of the plunger of each hydraulic actuator at least in part from a rotary position sensor signal output by the rotary position sensor of the corresponding hydraulic actuator and wherein the hydraulic actuators are operated in synchronization by the controller. 
     
     
         6 . The hydraulic cylinder position sensing and locking system of  claim 1 , wherein the desired range of the spacing of the lock nut relative to the hydraulic cylinder is about one millimeter to about six millimeters. 
     
     
         7 . The hydraulic cylinder position sensing and locking system of  claim 1 , wherein upon a stoppage of movement of the plunger, the drive unit continues to turn the lock nut such that the lock nut seats against retraction of the plunger. 
     
     
         8 . The hydraulic cylinder position sensing and locking system of  claim 1 , wherein upon a stoppage of movement of the plunger, the drive unit turns the lock nut such that the lock nut is spaced a distance from the hydraulic cylinder, and the controller selectively supplies hydraulic fluid under pressure to the hydraulic cylinder to lower the plunger such that the lock nut seats against retraction of the plunger. 
     
     
         9 . The hydraulic cylinder position sensing and locking system of  claim 1  wherein prior to any movement of the plunger in the retraction direction, the drive unit turns the lock nut such that the lock nut moves out of being seated against retraction of the plunger. 
     
     
         10 . The hydraulic cylinder position sensing and locking system of  claim 1 , wherein the drive unit includes:
 a motor;   a gear reduction unit;   a drive gear with teeth; and gear teeth on the lock nut;   wherein the teeth on the drive gear mesh with gear teeth on the lock nut.   
     
     
         11 . The hydraulic cylinder position sensing and locking system of  claim 1 , wherein before rotating the lock nut to unseat the lock nut, hydraulic fluid under pressure is introduced to the hydraulic cylinder to relieve friction on the lock nut. 
     
     
         12 . A hydraulic cylinder position sensing and locking system, comprising:
 a hydraulic actuator including:
 a hydraulic cylinder; and 
 a plunger including a piston in the hydraulic cylinder and a threaded rod that extends axially from so as to move with the piston, the plunger being moveable axially relative to the cylinder in an extension direction and a retraction direction by selective supply of hydraulic fluid under pressure to the hydraulic cylinder; 
   a lock nut that rotatably engages the threaded rod with a threaded connection therebetween;   a drive unit that can be operated to rotate the lock nut relative to the plunger;   a distance sensor that outputs a distance signal that is indicative of the axial spacing of the lock nut relative to the hydraulic cylinder; and   a controller that receives as an input the distance signal and outputs a control signal to control the drive unit so as to turn the lock nut in correspondence with the axial movement of the plunger so as to maintain the spacing of the lock nut relative to the hydraulic cylinder within a desired range.   
     
     
         13 . The hydraulic cylinder position sensing and locking system of  claim 12 , wherein upon a stoppage of movement of the plunger, the drive unit continues to turn the lock nut such that the lock nut seats against retraction of the plunger. 
     
     
         14 . The hydraulic cylinder position sensing and locking system of  claim 12 , wherein upon a stoppage of movement of the plunger, the drive unit turns the lock nut such that the lock nut is spaced a distance from the hydraulic cylinder, and the controller selectively supplies hydraulic fluid under pressure to the hydraulic cylinder to lower the plunger such that the lock nut seats against retraction of the plunger. 
     
     
         15 . The hydraulic cylinder position sensing and locking system of  claim 12 , wherein prior to any movement of the plunger in the retraction direction, the drive unit turns the lock nut such that the lock nut moves out of being seated against retraction of the plunger. 
     
     
         16 . The hydraulic cylinder position sensing and locking system of  claim 12 , wherein before rotating the lock nut to unseat the lock nut, hydraulic fluid under pressure is introduced to the hydraulic cylinder to relieve friction on the lock nut. 
     
     
         17 . The hydraulic cylinder position sensing and locking system of  claim 12 , further comprising a rotary position sensor that provides a signal indicative of a rotary position of the drive unit, an axial position of the plunger determined at least in part based on the rotary position sensor signal. 
     
     
         18 . The hydraulic cylinder position sensing and locking system of  claim 12 , wherein the system determines the axial position of at least one of the plunger and the piston at least partially based on the distance signal. 
     
     
         19 . The hydraulic cylinder position sensing and locking system of  claim 12 , wherein there is at least an additional hydraulic actuator and corresponding lock nut, drive unit, and distance sensor as claimed in  claim 12 , and wherein each hydraulic actuator, drive unit, and distance sensor is connected to the controller and the controller determines the axial position of the plunger of each hydraulic actuator at least in part from a rotary position sensor signal output by the rotary position sensor of the corresponding hydraulic actuator and wherein the hydraulic actuators are operated in synchronization by the controller. 
     
     
         20 . The hydraulic cylinder position sensing and locking system of  claim 12 , wherein the desired range of the spacing of the lock nut relative to the hydraulic cylinder is about one millimeter to about six millimeters. 
     
     
         21 . The hydraulic cylinder position sensing and locking system of  claim 12 , wherein the drive unit includes:
 a motor;   a gear reduction unit;   a drive gear with teeth; and   gear teeth on the lock nut;   wherein the teeth on the drive gear mesh with gear teeth on the lock nut.