JP2006515409A - Position control system for fluid operated cylinders - Google Patents

Abstract

A position control system is used to control the fluid operated cylinder 12, which is defined by a piston 18 located within the housing 20 and moving between a first end limit 22 and a second end limit 24 of travel. At least one fluid chamber 14. The system includes at least two electronically actuated proportional flow control valves 26, 30 that are connected to each of the respective ports of the cylinder to selectively and proportionally flow fluid into and out of at least one chamber. Control. At least one pressure sensor 38, 40 is provided to measure fluid pressure for each chamber. At least one separate position sensor 42 is positioned adjacent to the midpoint of the cylinder to sense the individual center position of the piston. The controller 44 includes a program and is operably connected to the at least two valves in response to the pressure measured by the at least one pressure sensor and the position measured by the at least one position sensor. Control startup.

Description

This application is a continuation application of provisional application 60 / 442,191 filed on January 23, 2003, a continuation application of provisional application 60 / 471,031 filed on May 16, 2003, April 2003. This is a continuation application of provisional application No. 60 / 460,549, filed four days, all of which are hereby incorporated by reference in their entirety.
The present invention relates to an accurate position control system for a fluid operated cylinder having at least one expandable chamber defined by a housing and a movable piston.

  The sale of cylinder positioning systems has hitherto generally fall into one of two categories: simple and complex. Simple systems are low cost and typically use time switches or limit switches to provide control. This type of system is significantly more cost-effective, but has some performance drawbacks. Limit switch systems do not have the ability to dynamically change one or more points at which the cylinder stops. Timing control systems require constant pressure, constant load, and constant wear. The complex system tolerates more changes in pressure, load, and wear, but has disadvantages in cost and complexity. Complex systems can cost 10 to 20 times more than simple systems. Complex systems typically require trained and experienced personnel to use and install fragile or costly sensor technology.

  In the present invention, it is desirable to provide a low cost, accurate fluid operated cylinder positioning system. It would be desirable to provide a system that is relatively durable against changes in pressure, load, and wear while maintaining low cost and simplicity. Accordingly, the present invention discloses an accurate and low cost fluid operated cylinder positioning system and method. According to the present invention, positioning the main stage of a cylinder or valve based on the pressure difference is a lower cost and feasible control method that is completely different from what industry leaders currently present. obtain. The present invention uses standard, low cost components and techniques to achieve control with accuracy approaching that of high cost systems, but at a cost comparable to simple systems.

  The position control system according to the invention is used in a fluid-operated cylinder, but at least one fluid chamber which it has is located in the housing and moves between a first end limit and a second end limit of travel. Defined by the piston to be The system includes at least two electronically actuated proportional flow valves that are connected to each port of the controlled fluid operated cylinder to enter and exit at least one fluid chamber of the controlled fluid operated cylinder. Selectively and proportionally control fluid flow. At least one pressure sensor is provided for measuring the fluid pressure for each chamber of the fluid operated cylinder to be controlled. At least one separate position sensor is positioned adjacent to the midpoint of the controlled fluid operated cylinder to sense the individual center position of the piston within the cylinder. The control program according to the present invention is operatively connected to at least two valves, at least one pressure sensor, and at least one position sensor, the pressure measured by the at least one pressure sensor, and at least one In response to the position measured by the sensor, it controls the activation of at least two valves.

Other uses of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for carrying out the invention is read in conjunction with the accompanying drawings.
The description herein refers to the accompanying drawings, in which like reference numerals refer to like parts throughout the several views.

  The present invention implements a pneumatic cylinder control scheme at a cost comparable to a simple system, but at a performance approaching that of a complex system. The control scheme according to the present invention is a combination of hardware and software. The hardware supports the necessary functions. However, the actual operation is determined by software. In addition, the software is constructed such that the variable part determines the actual final behavior. This approach allows, for example, control of various motion profiles, ie acceleration / deceleration profiles, speed, timing, force, repetition, etc. Furthermore, this control scheme allows the operation of either a double working cylinder or a single working cylinder. In other words, the present invention can operate a cylinder with fluid control on both sides, or a cylinder with a mechanism such as a spring that causes fluid control on one side and regression on the other side. Although the description contained herein is directed to pneumatically actuated cylinders, the control scheme described herein according to the present invention also applies to other fluids such as hydraulic hydraulics or other liquids. In still other applications of this control scheme, the cylinder can be replaced with a main stage valve. These are usually very large valves. In this case, the control scheme acts as a proportional guide for the main stage, allowing proportional positioning of the main stage valve. Traditionally, the valve industry has used complex methods such as torque motors or proportional valves with accurate feedback to control such main stage valves. The device used in this application is called valve positioning control. The control scheme described herein according to the present invention can therefore be used in place of existing positioning controls. Similar to the cylinder, the main stage valve can be operated with a variety of fluids and can operate as a dual-acting main stage positioner or as a single-acting main stage positioner.

According to the present invention, a method of controlling a standard pneumatic cylinder with reasonable accuracy can be developed by monitoring and changing the pressure on one or both sides of the piston. The basic theory behind this type of cylinder control is that if a known volume, i.e. a cylinder chamber, has a given amount of air pressure within that known volume, it exerts a known force on the chamber. This is shown by the following basic formula:
Force = pressure x area (1)
With a known load and some reasonable assumptions about friction, the force on each side of the piston of the pneumatic cylinder can be calculated. These forces directly correspond to a piston moving a known distance. The theory behind this assumption is proved in the next section.

To carry out this type of control, three variable parts are monitored. First, two signals corresponding to the pressure in both chambers of the cylinder are required. This is accomplished by a pressure transducer at each inlet of the cylinder. In addition, Hall effect sensors, or other types of separate position sensors, are used in the middle of the stroke to occasionally readjust the system, thus maintaining the accuracy of the system.
For the initial concept, assume that some variable parts are known and constant. These include cylinder load, friction, and wear. In the present invention, these can also be determined and compensated for in real time using general measurements and control methods such as an adaptation algorithm, if desired.

For the purpose of illustrating this, inefficiencies such as compression heat, friction, and losses due to changes in air direction are ignored. This description applies to double acting cylinders, where the end with the bar is called the “load” end and the opposite end is called the “cap” end.
The equation that determines the relationship between the pressure differences in the two chambers is as follows:

Where P _c , V _c and T _c are the pressure, volume and temperature of chamber 1 (or cap end), and P _l , V _l and T _l are the pressure and volume of chamber 2 (or load end). , And temperature.
Assuming the temperatures are equal, the equation is simplified as follows:
P _c · V _c = P _l · V _l (3)
As already mentioned:
F = P ・ A (4)
Here, F, P, and A represent force, pressure, and area, respectively.

  This proves that the force exerted in the cylinder is a function of the pressure on its end of the piston multiplied by the effective area. The effective area of the piston cap end is simply the internal area of the cylinder and is represented by:

_Di is the inner diameter of the cylinder, and _Ac is the area of the cap end of the cylinder.
The piston load end area is simply the above equation minus the bar area:

If the area of the piston is known, the chamber volume can be stated as follows:
At the cap end:
V _c = A _c · L _c (7)
L _c is the length from the inner end of the cap end to the surface of the piston.
At the load end:
V _l = A _{l·L l} (8)
L ₁ is the length from the inner end of the cap end to the surface of the piston.

  Thus, the volume of air in the cylinder cap end is as follows:

The volume of air in the load end of the cylinder is as follows:

Combining this with Equation 2 gives:

Finally, the pressure required to move the cylinder a distance is:

  Referring now to FIG. 1, the implementation of the control method according to the present invention is converted by connecting a multi-valve arrangement such as a four-valve pack with two pressure transducers, ie each port of a fluid operated cylinder. This can be done by connecting the vessels one by one. This transducer can be a ready-made part that is commercially available from a manufacturer such as DigiKey. OpAmps can be used for signal processing of standard circuit configurations and applied to the analog input of the valve pack. A position control system 10 according to the present invention is shown in FIG. 1, wherein a fluid operated cylinder 12 that it controls has at least one fluid chamber 14, 16, which is located within a housing 20 and has a first stroke. It is defined by a piston 18 that moves between a first end limit and a second end limit 22,24. System 10 includes at least two electronically actuated proportional flow valves 26, 28, 30, 32 that are connected to respective ports 34, 36 of the fluid operated cylinder 12 to be controlled. Valves 26, 28, 30, 32 selectively and proportionally control fluid flow into and out of at least one fluid chamber 14, 16 of the fluid operated cylinder 12 being controlled. At least one pressure sensor 38, 40 is provided to measure fluid pressure for each chamber 14, 16 of the controlled fluid operated cylinder 12, respectively. At least one separate position sensor 42 is positioned adjacent to the midpoint of the fluid-operated cylinder 12 to be controlled to sense the individual center position of the piston 18 within the housing 20. The central processing unit 44 includes a control program and is operably connected to at least two valves 26, 28, 30, 32, at least one pressure sensor 38, 40, and at least one position sensor 42, and at least Responsive to the pressure measured by one pressure sensor 38, 40 and the position measured by at least one sensor 42, activation of at least two valves 26, 28, 30, 32 is controlled.

  At least one separate position sensor 42 is positioned adjacent to one end of the travel of the piston 18 of the housing 20 and the first position sensor 42 positioned adjacent to the midpoint of the fluid operated cylinder. And a second position sensor 46 or 48 that provides a gentle stop deceleration of the piston 18 before contacting the end wall of the housing 20 that defines the at least one chamber 14, 18. At least one chamber 14, 16 is adjacent to the first expandable fluid chamber 14 adjacent one end of the stroke of the piston 18 of the housing 20 and the other end of the stroke of the piston 18 of the housing 20. A second expandable fluid chamber 16. At least two electronically actuated proportional flow valves 26, 28, 30, 32 selectively select a fluid flow associated with the first expandable fluid chamber 14 into the first expandable fluid chamber 14, A first valve 26 that proportionally controls and a second that selectively and proportionally controls the fluid flow associated with the first expandable fluid chamber 14 and out of the first expandable fluid chamber 14. A valve 28 may be included.

  The at least one pressure sensor 38, 40 includes a first pressure sensor 38 associated with the first expandable fluid chamber 14 and a second pressure sensor 40 associated with the second expandable fluid chamber 16. Can be included. A third pressure sensor 50 can be provided to monitor the pressure of the pressurized fluid source. At least one separate position sensor 42 is positioned adjacent to the first position sensor 42 located adjacent to the midpoint of the fluid operated cylinder 12 and one end of the travel of the piston 18 of the housing 20. A second position sensor 46 that provides a gentle stop deceleration of the piston 18 before contacting the end wall of the housing 20 defining at least one chamber 14, 18, and the travel of the piston 18 of the housing 20. A third position sensor 48 positioned adjacent to the opposite end and providing a gentle stop deceleration of the piston before contacting the end wall of the housing 20 defining the second fluid chamber 16 may be included. .

  The control program according to the present invention corresponds to the central position of the piston in the housing 20 when the piston 18 is sensed by at least one separate position sensor 42 located adjacent to the intermediate position relative to the housing 20. A fixed position can be initialized. The control according to the present invention allows at least one expandable fluid chamber 14, 16 to move the piston 18 a desired distance within the housing 20 from a discrete central position intermediate to the housing 20. A value corresponding to the amount of pressure required can also be calculated. The control program controls at least two electronically activated proportional flow control valves 26, 28, and / or 30, 32 to produce a calculated pressure corresponding to the desired travel distance of the piston 18 within the housing 20 at least one. Can be obtained in two expandable fluid chambers 14,16. Various means can be provided to bias the piston 18 toward individual central positions relative to the housing 20. Where only a single expandable fluid chamber is provided to be controlled by the present invention, the biasing means includes, by way of example and not limitation, any suitable mechanical device such as a return spring force. Can do. If two expandable fluid chambers 14, 16 are provided to be controlled by the system 10 according to the present invention, the biasing means corresponds to a second expandable fluid chamber. In determining the appropriate amount of pressure to apply to a single expandable fluid chamber, the pressure calculation detailed above can be modified to correspond to the pressure acting on the mechanical force of the spring. It should be recognized that the pressure calculation modifications can also be made to fit the double piston rod configuration, rather than the single rod piston configuration detailed herein.

  The cylinder 12 preferably has two expandable fluid chambers 14, 16 that operate, which cause changes in the position and force of the piston 18 and connecting rod. Two proportional control valves 26, 28 or 30, 32 are connected to each chamber 14, 16 respectively. One valve, by way of example and not limitation, moves fluid, such as compressed air or hydraulic oil, from the connection chamber, and the other valve supplies pressurized fluid to the connection chamber. The system includes control electronics 44 and preferably three pressure transducers 40, 42, 48. The control electronics 44, along with the on-board software, includes four proportional control valves 26, 28, 30, 32 in response to commands from an external source, such as, but not limited to, commands from a network or computer workstation. Control. The pressure transducers 38, 40, 50 monitor the pressure of the pressurized fluid supply and both expandable fluid chambers 14, 16, thereby allowing the pressurized fluid to enter and exit the expandable chambers 14, 16. The aim is to achieve precise positioning of the piston 18 and precise output of the connecting rod by controlling the metering. In a preferred configuration, the proportional control valves 26, 28, 30, 32 are a piezoelectric activated control valve of a type similar to that described in US Pat. No. 6,548,938 issued April 15, 2003, or 2003. US Design Patent No. D48335, issued December 9, 2003, PCT Publication Application No. WO 04/006349, issued July 3, 2003, or PCT Publication Application No. WO 03/083957, issued March 25, 2003 PCT publication application WO 03/067674 issued January 22, 2003, or PCT publication application WO 01/80326 issued March 29, 2001, or PCT issued March 29, 2001 It can be a type of piezoelectric actuated control valve similar to that described in published application WO 01/79731, all these The entire patent and application are hereby incorporated by reference. By way of example and not limitation, the piezoelectric starter uses current charge control for proportional valve operation by directly controlling the voltage across the piezoelectric starter or by monitoring the amount of energy in the piezoelectric starter It is preferably controlled by doing so, which is different from the pulse width modulation scheme used for proportional control of electromagnetically operated valves.

  Referring now to FIG. 2, as described in the control flow diagram, the software code simultaneously controls both pairs of valves on each side of the cylinder. The control program according to the present invention can best be understood with reference to FIG. The control program can be started by initializing the system at step 100. During the initialization step 100, the control program finds the home position or piston center position as indicated by the Hall effect sensor and applies pressure on both sides of the piston 18 to equalize the sides, and the piston 18 within the housing. Prevent from moving. By way of example and not limitation, the control system can provide a pressure of 50 psi on both sides of the cylinder while the cylinder is in the center position, which center position includes at least one position sensor 42 and at least one position sensor. This is demonstrated by the signals received from the pressure sensors 38,40. Once the system is initialized to step 100, the control program proceeds to question 102 to determine whether a change of position is desired. If a change of position is not desired, the control program returns to the beginning of question 102. If a change of position is desired, the control program proceeds to step 104 where the required pressure is calculated based on the desired movement. The control program then proceeds to question 106 where it is determined whether the desired position is towards the cap end of the cylinder 12. If the desired position is towards the cap end, the program branches to step 108 where the pressure is increased in the load end expandable fluid chamber of the cylinder 20. In response to query 106, if the desired position is not toward the cap end, the control program branches to step 110 where the pressure is increased in the cap end expandable fluid chamber of cylinder 20.

  After performing either step 108 or step 110, the program proceeds to question 112 where it is determined whether the pressures on both sides of the piston 18 are equal. If the pressures are not equal, the program branches to step 114 to monitor at least one position sensor 42 and reset the center position of the piston 18. After executing step 114, the control program returns to the beginning of question 112. If the pressure is equal in question 112, the control program proceeds to question 116 where it is determined whether the desired position is towards the load end of the cylinder 20. In response to query 116, if the desired position is towards the load end, the control program proceeds to step 118 where the pressure is reduced at the load end expandable fluid chamber of cylinder 20. In response to question 116, if the desired position is not towards the load end, the control program proceeds to step 120 where the pressure is reduced at the cap end expandable fluid chamber of cylinder 20.

  After performing either step 118 or 120, the program proceeds to question 122 to determine if the pressure on both sides of the piston 18 is equal. If the pressure on both sides of the piston 20 is not equal in response to the query 122, the control program proceeds to step 124 to monitor the at least one position sensor 42 and reset the center home position of the piston 18 in the housing 20. . After performing step 124, the control program returns to the beginning of question 122 to determine whether the pressures on both sides of piston 18 are equal. In response to question 122, if the pressure on both sides of piston 18 is equal, the control program proceeds to step 126 to indicate that piston 18 has completed movement, which has reached the desired position, This is because the current position is saved by the control program. After executing step 126, the control program returns to the beginning of question 102.

  The control program described in FIG. 2 corresponds to the cylinder 12, which has a first expandable fluid chamber 14 and a second expandable fluid chamber 16 located in the housing 20 and having a first stroke. It will be appreciated that it is defined by a piston 18 that moves between an end limit and a second end limit. If only one expandable fluid chamber is provided, the control program shown in FIG. 2 can be modified by eliminating question 116, steps 118, 120, question 122, and step 124. In this configuration, if the answer to question 112 is yes, the control program proceeds directly to step 126 and can proceed as described above. As already described in more detail, this configuration may include mechanical means such as, but not limited to, a mechanical force of a spring that biases the piston 18 toward a central home position relative to the housing 20.

  Although the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, the present invention is not limited to the embodiments disclosed herein, but rather is It is intended to cover various modifications and equivalent arrangements that fall within the spirit and scope of the section, and that scope encompasses all such modifications and equivalent structures that are allowed under the law. Is given the widest interpretation.

FIG. 4 is a simplified system diagram of a multi-valve configuration for controlling fluid flow for at least one expandable chamber of a fluid operated cylinder by means of a control program stored in memory. It is a simplified process flow diagram of a control program according to the present invention.

Claims (22)

A position control system for a fluid operated cylinder having at least one fluid chamber defined by a piston located within a housing and moving between a first end limit and a second end limit of travel,
At least two electrons coupled to each of the ports of the fluid operated cylinder to be controlled to selectively and proportionally control the fluid flow into and out of the at least one fluid chamber of the fluid operated cylinder to be controlled. A starting proportional flow valve;
At least one pressure sensor for measuring fluid pressure for each chamber of the fluid operated cylinder to be controlled;
At least one separate position sensor located adjacent to a midpoint of the fluid-operated cylinder to be controlled to sense a discrete central position of the piston in the cylinder;
The pressure measured by the at least one pressure sensor and the at least one position sensor operatively connected to the at least two valves, the at least one pressure sensor, and the at least one position sensor; And a control program for controlling activation of the at least two valves in response to the position measured by the position control system for a fluid operated cylinder. The at least one separate position sensor comprises:
A first position sensor located adjacent to a midpoint of the fluid operated cylinder;
A second located adjacent to one end of the piston travel in the housing to provide a gentle stop deceleration of the piston before contacting the end wall of the housing defining the at least one chamber; The position control system for a fluid operated cylinder according to claim 1, further comprising a position sensor.   A first valve associated with the first expandable fluid chamber for selectively and proportionally controlling fluid flow into and out of the first expandable fluid chamber; and the first expandable fluid. And further comprising the at least two electronically activated proportional flow valves including a second valve associated with the chamber for selectively and proportionally controlling fluid flow into and out of the first expandable fluid chamber. The position control system for a fluid operated cylinder according to claim 1.   A first expandable fluid chamber adjacent one end of the piston travel in the housing and a second expandable fluid chamber adjacent the other end of the piston travel in the housing; The position control system for a fluid-operated cylinder according to claim 1, further comprising at least one expandable fluid chamber including the preceding period.   At least one pressure sensor further comprising a first pressure sensor associated with the first expandable fluid chamber and a second pressure sensor associated with the second expandable fluid chamber; The position control system for a fluid operated cylinder according to claim 4, comprising:   A first position sensor located adjacent to a midpoint of the fluid actuated cylinder; and an end of the housing located adjacent to one end of the piston travel in the housing to define the one chamber. A second position sensor providing a gentle stop deceleration of the piston before contacting the wall, and positioned adjacent to the other end of the piston travel in the housing to define another chamber; 5. The position control system for a fluid operated cylinder according to claim 4, further comprising a third position sensor for providing a gentle stop deceleration of the piston before contacting the end wall of the housing.   2. A control program for initializing a home position when the piston is sensed by at least one separate position sensor located adjacent to an intermediate position relative to the housing. Position control system for fluid operated cylinders.   Calculating the pressure in the at least one expandable fluid chamber required to move the piston a desired distance within the housing from a discrete central position intermediate to the housing; and A control program for controlling the at least two electronically activated proportional flow valves to obtain a calculated pressure in the at least one expandable fluid chamber corresponding to a desired travel distance of the piston in the housing; The position control system for a fluid operated cylinder according to claim 1, further comprising:   2. A position control system for a fluid operated cylinder according to claim 1, further comprising means for biasing the piston toward individual central positions relative to the housing. A position control system for a fluid operated cylinder having at least one fluid chamber defined by a piston located within a housing and moving between a first end limit and a second end limit of travel,
Selective and proportional to fluid flow in and out of at least one fluid chamber of the fluid operated cylinder controlled by at least two electronic symbolic proportional flow valves connected to each port of the fluid operated cylinder to be controlled. Step to control automatically,
Measuring fluid pressure for each chamber of the fluid operated cylinder controlled by at least one pressure sensor;
Sensing an individual center position of the piston within the cylinder by at least one separate position sensor located adjacent to a midpoint of the fluid operated cylinder to be controlled;
A pressure measured by the at least one pressure sensor by a control program operably connected to the at least two valves, the at least one pressure sensor, and the at least one position sensor; and the at least one Controlling the activation of at least two valves in response to the positions measured by the two position sensors. A position sensing step by the at least one separate position sensor;
Positioning a first position sensor adjacent to a midpoint of the fluid operated cylinder;
Positioning a second position sensor adjacent one end of the piston travel in the housing;
Sensing by the second position sensor an individual position adjacent to one end of the piston travel relative to the housing;
Responsive to the second position sensor, causing the control program to decelerate the piston to a gentle stop before contacting the end wall of the housing defining the at least one chamber; The position control system for a fluid operated cylinder according to claim 10, further comprising: Controlling fluid flow by the at least two electronically activated proportional flow valves;
Providing a first valve associated with the first expandable fluid chamber for selectively and proportionally controlling fluid flow entering the first expandable fluid chamber;
Providing a second valve associated with the first expandable fluid chamber to selectively and proportionally control fluid flow exiting the first expandable fluid chamber. A position control system for a fluid operated cylinder according to claim 10. The at least one expandable fluid chamber comprises:
Providing a first expandable fluid chamber adjacent one end of the piston travel in the housing;
11. A position control system for a fluid operated cylinder according to claim 10, further comprising providing a second expandable fluid chamber adjacent to the other end of travel of the piston in the housing. . The pressure sensing step by the at least one pressure sensing comprises:
Providing a first pressure sensor associated with the first expandable fluid chamber;
The position control system for a fluid operated cylinder of claim 13, further comprising providing a second pressure sensor associated with the second expandable fluid chamber. A position sensing step by the at least one separate position sensor;
Providing a first position sensor located adjacent to a midpoint of the fluid operated cylinder;
Second position sensing located adjacent to one end of the piston travel in the housing to provide a gentle stop deceleration of the piston before contacting the end wall of the housing defining the one chamber Providing a vessel;
A third position sensor located adjacent to the opposite end of the piston travel in the housing to provide a gentle stop deceleration of the piston before contacting the end wall of the housing defining another chamber 14. The position control system for a fluid operated cylinder according to claim 13, further comprising the step of: The step of controlling by the control program comprises:
The method of claim 10, further comprising initializing a home position when the piston is sensed by the at least one separate position sensor and positioned at a separate central position relative to the housing. Position control system for fluid operated cylinders. The step of controlling by the control program comprises:
Calculating the pressure in the at least one expandable fluid chamber required to move the piston a desired distance within the housing from a discrete central position intermediate to the housing;
Controlling the at least two electronically activated proportional flow valves to obtain a calculated pressure in the at least one expandable fluid chamber corresponding to a desired travel distance of the piston in the housing. The position control system for a fluid operated cylinder according to claim 10, further comprising:   11. The position control system for a fluid operated cylinder according to claim 10, further comprising biasing the piston in the first direction toward a discrete central position relative to the housing. A position control system for a fluid operated cylinder having two fluid chambers defined by a piston located within a housing and moving between a first end limit and a second end limit of travel,
Two valves are connected to each port of the fluid operated cylinder to be controlled to selectively and proportionally control the fluid flow in and out of the two fluid chambers of the fluid operated cylinder to be controlled 4. Two electronically actuated proportional flow valves,
Two pressure sensors, one pressure sensor measuring fluid pressure for each chamber of the fluid-operated cylinder to be controlled;
At least one separate position sensor located adjacent to the midpoint of the fluid-operated cylinder to be controlled to sense individual center positions of pistons within the cylinder;
Pressure measured by the two pressure sensors and measured by the at least one position sensor operatively connected to the four valves, the two pressure sensors, and the at least one position sensor. And a control program for controlling activation of the four valves in response to the determined position.   At least one separate position sensor including a first position sensor positioned adjacent to a midpoint of the fluid-operated cylinder; and positioned adjacent to one end of the piston travel in the housing. A second position sensor for providing a gentle stop deceleration of the piston before contacting the end wall of the housing defining the first chamber, and a position adjacent to the opposite end of the piston travel in the housing The fluid actuated of claim 19, further comprising a third position sensor for providing a gentle stop deceleration of the piston before contacting an end wall of the housing defining a second chamber. Position control system for cylinders.   20. The control program of claim 19, further comprising a control program for initializing a home position when the piston is sensed by the at least one separate position sensor located adjacent to an intermediate position relative to the housing. Position control system for fluid operated cylinders.   In each of the first expandable fluid chamber and the second expandable fluid chamber, the piston is moved a desired distance within the housing from an individual central position intermediate to the housing. Calculating the pressure required to move and controlling the four electronically activated proportional flow valves to obtain a calculated pressure corresponding to the desired travel distance of the piston within the housing; 20. The position control system for a fluid operated cylinder according to claim 19, further comprising the control program acquired in each of the expandable fluid chamber and the second expandable fluid chamber.

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