WO1993014371A1

WO1993014371A1 - Cylinder piston position detection apparatus

Info

Publication number: WO1993014371A1
Application number: PCT/US1992/009736
Authority: WO
Inventors: Gerald A. Gegel; Dwayne E. Tharp
Original assignee: Caterpillar Inc.
Priority date: 1992-01-13
Filing date: 1992-11-09
Publication date: 1993-07-22

Abstract

Position detecting devices are commonly utilized in conjunction with hydraulic cylinders in order to measure the extension of the piston from the cylinder and relate the piston extension to the various characteristics necessary to exercise control over an apparatus utilized in conjunction with the cylinder. Advantageously, such systems should provide accurate and repeatable position information and should be able to be utilized with a variety of cylinders in actual industrial environments. The subject position detecting system includes a stretched magnetostrictive member (106) axially aligned with and located along a wall of a cylinder (104). A magnet (108) is fixedly attached to a movable piston (102) associated with the cylinder (104). A control (110) produces and delivers a start signal to the magnetostrictive member (106), receives a stop signal from the magnetostrictive member (106), and produces a time signal responsive to the elapsed time between the start and stop signals. This time signal is interpreted to provide a signal corresponding to the actual position of the piston (102) relative to the cylinder (104).

Description

De script ion

CYLINDER PISTON POSITION DETECTION APPARATUS

Technical Field

This invention relates generally to an apparatus for detecting the position of a piston movable within a cylinder and, more particularly, to an apparatus for utilizing a magnetostrictive element to detect the position of a piston within a cylinder.

Background Art

A variety of systems have bee utilized in the past to sense the displacement of the movable element or piston in a cylinder such as a hydraulic cylinder. This detected position is then utilized in control strategies that require knowledge of the piston extension. Such prior systems must overcome problems with mounting the sensing devices and must be able to survive in the often harsh environmental conditions to which they are exposed.

One particularly advantageous system treats the hydraulic cylinder cavity as a resonant chamber that is capable of containing a microwave pulse, and utilizes sophisticated electronics to detect relationships relative to such a pulse in order to determine the size of the cavity and resulting piston extension. Such prior systems have the advantage of providing piston extension information without the need for attachment of mechanical sensors to the hydraulic apparatus. However, the electronics for such systems are somewhat complex, making the systems more suitable in some applications than others. Also, the use of the cylinder cavity as a resonant device generally requires that the cavity be formed of metallic elements or in some manner lined with metallic elements. As the industry moves toward the use of non-metallic hydraulic cylinders it is advantageous to provide a position sensing device that is easily utilized in such cylinders.

The present invention is directed at overcoming one or more of the problems as set forth above.

Disclosure of the Invention

In one aspect of the present invention, an apparatus is provided for detecting the position of a piston movable within a cylinder. A stretched magnetostrictive member is axially aligned with and located along a wall of the cylinder, and a magnet is fixedly attached to the movable piston. A control produces and delivers a start signal to the magnetostrictive member, receives a stop signal from the magnetostrictive member, and produces a time signal responsive to the elapsed time between the start and stop signals.

The present invention provides a position detecting system that is advantageously easy to implement in both ferrous and nonferrous hydraulic cylinders.

Brief Description of the Drawings

For a better understanding of the present invention reference may be made to the accompanying drawings, in which:

Fig. 1 is a combination block diagram and side elevational view of a hydraulic cylinder incorporating one embodiment of the present invention; Fig. 2 is an enlarged section of a portion of the hydraulic cylinder depicted in Fig. 1; Fig. 3 is a block diagram of an embodiment of the present invention; and.

Fig. 4 is a chart of time traces relating to operation of the embodiment depicted in the forgoing figures.

Best Mode for Carrying Out the Invention

Referring first to Figs. 1-3, an apparatus embodying certain of the principles of the present invention is generally indicated by the reference numeral 100. It should be understood that the following detailed description relates to the best presently known embodiment of the apparatus 100. However, the apparatus 100 can assume numerous other embodiments, as will become apparent to those skilled in the art, without departing from the appended claims.

The apparatus 100 includes a hydraulic cylinder 104 containing a movable piston 102. This is a conventional piston design with no particular modifications to suit the instant invention. A stretched magnetostrictive member 106 is axially aligned with and located along a wall of the cylinder 104. In the preferred embodiment the magnetostrictive member 106 is actually positioned within a wall of the cylinder 104.

Also in the preferred embodiment, the cylinder walls surrounding the magnetostrictive member 106 are composed of substantially nonferrous material. This can be a nonferrous stainless steel material as is used in some conventional hydraulic cylinders or it can be a polymer matrix composite material.

A magnet 108 is fixedly attached to the movable piston 102. The magnet is advantageously of a rare earth material producing a high flux density. As shown in particular detail in Fig. 2, the magnet 108 can be included in a circular carrier positioned around an end of the movable piston 102. It is not necessary that the magnet 108 be so constructed or positioned. Alternative designs could be easily constructed utilizing non circular carriers for the magnet 108 and positioning the magnet 108 at other fixed locations along the piston 102. Adaptations of the design shown will be obvious to those skilled in the art.

A control means 110 produces and delivers a start signal to the magnetostrictive member 106, receives a stop signal from the magnetostrictive member 106, and produces a time signal responsive to the elapsed time between the start and stop signals.

Working in cooperation with the control means 110 is a transducer 112 adapted to produce an electrical stop pulse in response to a mechanical disturbance of the magnetostrictive member 106. This mechanical disturbance is produced when flux lines produced by the magnet 108 intersect the magnetostrictive member 106 at locations responsive to the position of the magnet 108 along the member 106 causing a torsional defection of the magnetostrictive member 106. The control means 110 detects the electrical stop pulse and produces the responsive stop signal.

The transducer means 112 is preferably mounted in a housing 116 attached to the cylinder 104. Although various structural arrangements can be envisioned for accomplishing the function of the transducer 112, one embodiment advantageously utilizes a coil member 118 attached to the magnetostrictive member 106. Mounted adjacent to the coil member 118 is a permanent magnet 120. Torsional defection of the magnetostrictive member 106 causes the coil member 118 to move relative to the magnet 120 and produces an electrical disturbance in the coil member 118. This electrical disturbance is delivered to a pulse detector 122 associated with the control means 110. The control means 110 also includes a pulse generator 124 that has an output line connected to the magnetostrictive member 106. The output line from the pulse generator 124 is also connected to an input terminal of a timer 126, as is an output terminal of the pulse detector 122.

The control means 110 also includes interpreter means 114 for receiving the time signal and relating the time signal to the position of the magnet 108 relative to the magnetostrictive member 106. The timer 126 is connected to the interpreter means 114. An output line from the interpreter means 114 is provided to deliver a signal indicative of piston position to whatever control device it is desired to utilize in conjunction with such a position signal.

In one embodiment of the instant invention, the interpreter means 114 also determines at least one of the velocity and acceleration of the piston 102 in response to successive time signals. In other words, by obtaining successive position determinations and relating these to the distance traveled over a known period of time, both the acceleration and velocity of the piston 102 can be interpreted and delivered to a control device.

Industrial Applicability

Operation of the apparatus 100 is best described in relation to Figs. 1-3 and with reference to the time traces found in Fig. 4. The pulse generator 124 produces a continuous stream of short duration electrical pulses at a predetermined frequency. These pulses are delivered to the magnetostrictive member 106 at a first end of the member 106. The magnetostrictive member 106 acts as a waveguide, conducting the pulses along the length of the member 106.

At some point along the length of the magnetostrictive member 106 the flux lines from the magnet 108 intersect the member 106. At this point, as is known in the magnetostrictive art, a torsional deformation takes place in the magnetostrictive member 106 causing movement of the coil member 118. This movement relative to the magnet 120 causes an electrical disturbance that is detected by the pulse detector 122 and transformed into a stop signal.

Both the start and stop signals are delivered to the timer 126. The timer 126 is not described in detail in this application because it is well known in the art to provide various sorts of electronic timers for determining the period of time elapsed between two electrical signals. For example, the start signal from the pulse generator 124 can initiate a counter driven by a high speed clock. The counter will accumulate clock pulses until it is stopped by the stop signal from the pulse detector 122. The number of clock pulses accumulated in the counter would then be an indication of the amount of time that elapsed between the two electrical signals. However, various other mechanisms for determining the duration between the two electrical signals are well known in the art and such arrangements can be utilized in conjunction with the embodiment described herein.

A signal from the timer 126 representing the duration between the start and stop signals is delivered to the interpreter 114. The interpreter 114 then utilizes one of any number of methods to determine the position of the magnet 108 and hence the piston 102 relative to the magnetostrictive member 106 and the cylinder 104. For example, the interpreter 114 can utilize a simple lookup table in a memory associated with the control means 110. Various numbers of clock count accumulations from the timer 126 can be directly related in such a lookup table to the actual distance of the piston displacement. Other methods of interrelating the time between start and stop signals to the displacement of the piston 102 will be evident to those skilled in the art.

This position signal is then delivered for use by whatever sort of control device is needed to utilize the position related information. It would be equally possible to directly deliver the signal from the timer 126, thereby eliminating the need to include the interpreter in the control means 110. This is entirely a matter of design choice. Additionally, the output from the interpreter 114 can be either an analog or a digital signal depending upon the needs of the user of the apparatus 100. Mechanisms for converting between analog and digital signals are well known in the art. In addition to determining piston position, the interpreter 114 can readily interpret both velocity and acceleration information based on utilization of the apparatus 100. By simply making multiple piston position determinations and relating the distance moved by the piston 102 over a known period of time, both the velocity and acceleration can be readily calculated in manners well known in the art. Therefore, the information that can be delivered by the interpreter 114 to a control mechanism includes not only piston position but also piston velocity and acceleration information.

Referring to Fig. 4. trace "A" shows the succession of start signals delivered from the pulse generator 124 to the magnetostrictive element 106. Delivery of a start signal causes the timer 126 to internally generate a rising edge of a start pulse. As the start pulse produced by the start signal travels along the magnetostrictive member 106 it eventually encounters the distortion produced by the intersection of the flux lines from the magnet 108 with the magnetostrictive member 106. This produces an electrical disturbance in the coil member 118 as is shown in the trace "B". This electrical disturbance is delivered to the pulse detector 122, producing the stop signal shown in trace "C". This signal is delivered to the timer 126, ending the timing pulse that was initiated by the start signal of trace ^MA^M. It is this pulse width, shown as trace "D", that is measured by the timer 126 and delivered to the interpreter means 114.

Other aspects, objects, advantages and uses of this invention can be obtained from a study of the drawings, the disclosure and the appended claims.

Claims

1. An apparatus (100) for detecting the position of a piston (102) movable within a cylinder (104) , comprising: a stretched magnetostrictive member (106) axially aligned with and located along a wall of said cylinder (104) ; a magnet (108) fixedly attached to said movable piston (102) ; and control means (110) for producing and delivering a start signal to said magnetostrictive member (106) , receiving a stop signal from said magnetostrictive member (106) , producing a time signal responsive to the elapsed time between said start and stop signals, and determining at least one of the velocity and acceleration of said piston (102) in response to successive time signals.

2. An apparatus (100), as set forth in claim 1, wherein said start signal is an electrical pulse.

3. An apparatus (100), as set forth in claim 2, wherein said magnetostrictive member (106) acts as a waveguide for said electrical start pulse, which travels along said magnetostrictive member (106) at a predetermined rate.

4. An apparatus (100), as set forth in claim 1, wherein said magnet (108) produces flux lines that intersect said magnetostrictive member (106) at locations responsive to the position of said magnet (108) along said member (106) , and wherein the intersection of said flux lines produces a mechanical disturbance in said magnetostrictive member (106) .

5. An apparatus (100) , as set forth, in claim 4, including a transducer (112) adapted to produce an electrical stop pulse in response to said mechanical disturbance.

6. An apparatus (100), as set forth in claim 5, wherein said control means (110) detects said stop pulse and produces a responsive stop signal.

7. An apparatus (100), as set forth in claim 1, wherein said control means (110) includes interpreter means (114) for receiving said time signal and for relating said time signal to the position of said magnet (108) relative to said magnetostrictive member (106) .

8. An apparatus (100), as set forth in claim 1, wherein said magnetostrictive member (106) is positioned within said cylinder wall.

9. An apparatus (100), as set forth in claim 8, wherein said cylinder wall surrounding said magnetostrictive member (106) is composed of substantially nonferrous material.

10. An apparatus (100), as set forth in claim 9, wherein said nonferrous material is a polymer matrix composite.

11. An apparatus (100) , as set forth in claim 1, wherein said magnet (108) is a rare earth permanent magnet.

12. An apparatus (100) for detecting the position of a piston (102) movable within a cylinder (104) , comprising: a stretched magnetostrictive member (106) axially aligned with and positioned within a wall of said cylinder (104) ; a permanent magnet (108) fixedly attached to said movable piston (102) in a manner sufficient to produce flux lines that intersect said magnetostrictive member (106) at locations responsive to the position of said magnet (108) along said member (106) , and wherein the intersection of said flux lines produces a mechanical disturbance in said magnetostrictive member (106) ; transducer means (112) for producing an electrical stop pulse in response to said mechanical disturbance; and control means (110) for producing and delivering an electrical pulse start signal to an end of said magnetostrictive member (106) , receiving said stop pulse from said transducer means (112) and producing a responsive stop signal, and producing a time signal responsive to the elapsed time between said start and stop signals, and wherein said control means (110) includes interpreter means (114) for receiving said time signal, relating said time signal to the position of said magnet (108) relative to said magnetostrictive member (106) , and determining at least one of the velocity and acceleration of said piston (102) in response to successive position determinations.

13. An apparatus (100), as set forth in claim 12, wherein said cylinder wall surrounding said magnetostrictive member (106) is composed of substantially nonferrous material.

14. An apparatus (100), as set forth in claim 13, wherein said nonferrous material is a polymer matrix composite.