Hydraulic cylinder position sensing and locking system and corresponding method

A method of locking and sensing the position of a hydraulic cylinder comprising the steps of:

• providing a hydraulic actuator that includes:
• a hydraulic cylinder, and
• 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 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;
• providing a lock nut that rotatably engages the threaded rod with a threaded connection therebetween;
• providing a drive unit that can be operated to rotate the lock nut relative to the plunger;
• providing a distance sensor that outputs a distance signal that is indicative of the axial spacing of the lock nut relative to the hydraulic cylinder;
• providing a controller that receives as an input the distance signal and outputs a control signal to control the drive unit;
• programming the controller to provide the signal to control the drive unit such that the drive unit turns 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, and
• programming the controller such that 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 that may prohibit rotating of the lock nut.

A synchronous hydraulic cylinder position sensing and locking system, comprising:

• at least two hydraulic actuators, each 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 axial ly 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 corresponding lock nut for each hydraulic actuator that rotatably engages the threaded rod with a threaded connection therebetween;
• a corresponding drive unit for each hydraulic actuator that can be operated to rotate the lock nut relative to the plunger;
• a corresponding distance sensor for each hydraulic actuator that outputs a distance signal that is indicative of the axial spacing of the lock nut relative to the hydraulic cylinder;
• a corresponding rotary position sensor for each hydraulic actuator that provides a signal indicative of rotary position of the drive unit, and
• a controller that receives the signal from the rotary position sensor of each hydraulic actuator to determine the axial position of the plunger of each hydraulic actuator at least in part from the rotary position sensor signal, maintains the difference between the axial positions of the plungers within a desired tolerance by selectively controlling the supply of hydraulic fluid under pressure that flows to each hydraulic cylinder, and receives as an input the distance signal of each distance sensor and outputs a control signal to control the corresponding drive units such that each drive unit turns the corresponding lock nut in correspondence with the axial movement of the corresponding plunger of each hydraulic actuator so as to maintain the spacing of each lock nut relative to the corresponding hydraulic cylinder within a desired range.

A method of synchronously lifting or lowering a load with hydraulic cylinders comprising the steps of:

• providing at least two hydraulic actuators that each include:
• a hydraulic cylinder, and
• 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 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;
• providing a corresponding lock nut for each hydraulic actuator that rotatably engages the threaded rod with a threaded connection therebetween;
• providing a corresponding drive unit for each hydraulic actuator that can be operated to rotate the lock nut relative to the plunger;
• providing a corresponding distance sensor for each hydraulic actuator that outputs a distance signal that is indicative of the axial spacing of the lock nut relative to the hydraulic cylinder;
• providing a corresponding rotary position sensor for each hydraulic actuator that provides a signal indicative of rotary position of the drive unit;
• providing a controller that receives as an input the distance signal of each distance sensor and receives the rotary position sensor signal;
• programming the controller to:
• determine the axial position of the plunger of each hydraulic actuator at least in part from the corresponding rotary position sensor signal,
• maintain the difference between the axial position of each plunger of the hydraulic actuators to stay within a desired tolerance by selectively controlling the supply of hydraulic fluid under pressure that flows to each hydraulic cylinder;
• and
• output a signal to each drive unit to turn the corresponding lock nut in correspondence with axial movement of the corresponding plunger so as to maintain the spacing of the lock nut relative to the corresponding hydraulic cylinder within a desired range;
• and
• operating the controller to synchronously lift or lower the load.