Technical Field Of The Invention

The present invention relates to an apparatus of and method for monitoring wear of a bushing integrated within a cylinder assembly, such as a hydraulic or pneumatic cylinder assembly.

Background

Hydraulic cylinders operate by applying pressure to a contained hydraulic fluid. The change in pressure causes a piston to move within a tubular (preferably cylindrically shaped) element commonly referred to as a cylinder barrel. A base or cap end seals the cylinder barrel at one end and a cylinder head seals the cylinder barrel at an opposite end. A shaft is typically attached to one end of the piston. The shaft extends through a bushing seal located in the cylinder head. The motion of the piston is translated to the shaft to operate a mechanical member.

The hydraulic cylinders rely upon a sealed system for reliable functionality. The sealed system relies upon a sealed interface provided between the piston and the internal surface of the cylinder barrel and a sealed interface provided between the shaft and the internal or shaft contact surface of the bushing for optimal operation.

Friction and other forces applied to the bushing by the motion of the shaft passing therethrough degrading the shaft contact surface of the bushing over time. The operation and reliability of the hydraulic cylinder is directly related to the quality of the seal provided between the shaft and the associated bushing. In use monitoring of the condition of the bushing surface can optimize servicing intervals and enhance the overall reliability of the hydraulic cylinder.

Several solutions include a wear detection groove arranged upon an inner peripheral surface of a bushing. The groove may be provided in a variety of

configurations. As the interface surface of the bushing wears, the groove gradually decreases until the groove disappears, indicating that the bushing is in need of replacement. These solutions require visual inspection. The visual inspection process is not continuous and is generally accomplished at established time intervals. The visual inspection process is also limited in its precision.

A second known solution integrates an insulated wire is placed in a form of a loop circumscribing the shaft, wherein the loop is positioned between the bushing and the shaft. Wear of the insulation is correlated to the wear of the bushing - shaft interface. As the insulation degrades, a current or signal strength provided through the wire also degrades. The current strength can be monitored, such as by an intensity of a light integrated into a circuit. A drop in current strength is correlated to the wear and ultimately, the directive for servicing the bushing. Another known solution embeds an integrated sensor into the seal. A first known embedded sensor is inserted radially into the seal and is therefore not conducive to a seal for rotating objects. A second known embedded sensor utilizes a series of circular shaped monitoring devices, each monitoring device being assembled between a pair of adjacently positioned plates. The circular shaped monitoring devices collectively form a capacitive monitoring system. The seal assembly includes multiple components. The components must be assembled together to precise tolerances. The capacitance is only useful for monitoring non-metallic materials, such as rubbers, plastics, and the like. The capacitance measurements are not very precise.

Another known solution embeds a wire within an interior surface of a bushing or bearing. An indicator monitors for continuity of the wire. The circuit is broken when the wire is worn through, thus identifying when the bushing needs servicing. This configuration is limited where the wire monitors only a small portion of the interface surface of the bushing.

Another known solution positions an electrically conductive counter body against a non-conductive sealing material fixed upon an electrically conductive sealing material of a dynamic sealing element. The electrically conductive counter body is placed into a circuit to monitor continuity between the electrically conductive counter body and the electrically conductive sealing material. The non-conductive material retains an open circuit until the non-conductive material is worn through. When the non-conductive material is worn through, the electrically conductive counter body contacts the electrically conductive sealing material closing the circuit. The circuit is monitored to determine when the non-conductive sealing material needs servicing.

Another known solution utilizes an optical fiber system for monitoring a condition of a seal. The fiber optic is embedded in the seal and operatively coupled to an interferometric system. The interferometric system, in combination with a

microprocessor, monitors and determines the condition of the seal. This system can be expensive and is limited to a specific region of the seal. The monitored section is equal to a width of the fiber optic strand.

Another known solution integrates transducers within sliding seals to monitor the condition of the seal. The transducers emit a wireless signal comprising data in the form of discrete measurement values and/or a status of an associated circuit. Wireless communications may not be reliable. Balancing of rotating equipment is essential to long- term reliability. The weight of the transducers may impact the operation and long-term reliability of the equipment. Another known solution integrates an acoustic wave device. The acoustic wave device utilizes an input transducer for generating a mechanical acoustic wave using a piezoelectric substrate and an output transducer for receiving the resulting acoustic wave and generating an output signal based upon the wave propagation between the input and output transducers. Limitations of this solution include expense of the transducers, weight and balance affects by the inclusion of the transducers, reliability of the transducers (particularly when subjected to mechanical shock, thermal changes, and the like), and other reliability impacts.

Another known solution integrates a magnetic interface onto an antifriction bushing. The sensor includes a giant magneto resistance element arranged at a distance from a magnetic coder. The coder forms a multipolar magnet with a pair of poles.

Magnetic measurements are limited in their precision. The cover needs to be assembled to the moving component (such as a shaft) in a manner to avoid interfering with the balance of the moving component. Addition of any weight to a moving object increases inertia of the object, thus increasing the required acceleration forces required to cause and maintain motion of the moving component. Another known solution integrates strain gauges into a seal. The system monitors the status of the strain gauges to determine when the seal needs servicing. Strain gauges are limited to a system that monitors a change in the shape of the material. A strain gauge might not identify wear of a seal, or more specifically, when material is removed from abrasion.

Each of the above known solutions has their limitations. There seems to be room for improvement.

SUMMARY OF THE INVENTION

The present invention is directed to an apparatus and respective method for monitoring a condition of a bushing or bearing within a cylinder, such as a hydraulic or pneumatic cylinder. In a first aspect of the present invention, an apparatus for monitoring a condition of bearing or bushing, the apparatus comprising: a bushing having a bushing aperture extending axially therethrough; a monitoring ring receiving groove extending radially outward from the bushing aperture; a monitoring ring comprising a plurality of conductive annular rings, each conductive annular ring being formed into a cylindrical shape about a longitudinal axis and laminated to one another, the monitoring ring being positioned within the monitoring ring receiving groove; and a conductive interface assembly comprising a plurality of conductive interfaces, each conductive interface provided in electrical communication with the respective conductive annular rings.

In a second aspect, the system further includes a processing device comprising a set of digital instructions for monitoring and analyzing electrical properties of each conductive annular ring obtained via said conductive interface. In another aspect, the processing device further comprising an input device for receiving an electrical signal from said conductive interface.

In another aspect, an electrically non-conductive section is provided across each conductive annular ring forming a continuous electrical pathway about a circumference of each respective conductive annular ring. In another aspect, each conductive annular ring is provided in electrical communication with the processing device via an electrically conductive interface. In another aspect, each conductive annular ring is fabricated of an electrically conductive material, such as copper foil, copper, gold, gold plated nickel, silver, and the like.

In another aspect, each thin dielectric base material annular ring layer is fabricated of one of polyimide, Polyether ether ketone, and transparent conductive polyester film, and the like.

In another aspect of the present invention, a method of determining a condition of bearing or bushing, the method comprising steps of: integrating a bushing into a cylinder, such as a hydraulic or pneumatic cylinder, the bushing comprising: a bushing aperture extending axially through said bushing, a monitoring ring receiving groove extending radially outward from said bushing aperture, and a bushing condition monitoring ring comprising a plurality of electrically conductive annular rings, each electrically conductive annular ring being formed into a cylindrical shape about a longitudinal axis and laminated to one another, the monitoring ring being positioned within said monitoring ring receiving groove; providing electrical communication between each said electrically conductive annular ring and a processing device; and monitoring said bushing condition monitoring ring for changes in electrical properties to determine a condition of the bushing.

What is desired is an apparatus and respective method of continuously monitoring a bushing or bearing seal without adding weight to the shaft.

The utilization of a plurality of layers is a low cost solution that provides the monitoring system with the ability to know exactly the thickness of wear of the interior surface of the bushing. This is done by the wear through of the different layers. The system can monitor the time span or total run hours between an initial installation and when the innermost layer of the monitoring ring is worn through. This can be utilized to provide predictive wear of the bushing to estimate service intervals. Additionally, the multiple layer configuration offers several different electrical properties to monitor the condition of the bushing. If an open circuit configuration is used, then measurement of the breakage of the circuit of a layer is used to indicate the amount of wear, in addition electrical connection to the piston can be detected, to thus use the information which open circuit is electrically coupled to the piston and then when the circuit of that layer breaks. Uneven wear could then also be detected. If a closed circuit configuration is used, then for example measurement for each layer of inductive, capacitive and/or electrical coupling to the piston can be used to determine the wear.

It is an apparatus and respective method of continuously monitoring a bushing or bearing seal without adding weight to the shaft/piston.

These and other features, aspects, and advantages of the invention will be further understood and appreciated by those skilled in the art by reference to the following written specification, claims and appended drawings, which follow.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature of the present invention, reference should be made to the accompanying drawings in which:

FIG. 1 presents an exemplary hydraulic cylinder assembly; FIG. 2 presents an isometric view of an exemplary bushing monitoring insert;

FIG. 3 presents a top view of the bushing monitoring insert originally introduced in FIG. 2;

FIG. 4 presents a sectioned view of the bushing monitoring insert originally introduced in FIG. 2, the section taken along section line 4—4 of FIG. 3; FIG. 5 presents an exemplary schematic block diagram of the monitoring system; and

FIG. 6 presents a top view of a modified bushing monitoring insert utilizing a continuity circuit monitoring configuration.

Like reference numerals refer to like parts throughout the several views of the drawings.

MODES FOR CARRYING OUT THE INVENTION

The following detailed description is merely exemplary in nature and is not intended to limit the described embodiments or the application and uses of the described embodiments. As used herein, the word "exemplary" or "illustrative" means "serving as an example, instance, or illustration." Any implementation described herein as

"exemplary" or "illustrative" is not necessarily to be construed as preferred or advantageous over other implementations. All of the implementations described below are exemplary implementations provided to enable persons skilled in the art to make or use the embodiments of the disclosure and are not intended to limit the scope of the disclosure, which is defined by the claims. For purposes of description herein, the terms "upper", "lower", "left", "rear", "right", "front", "vertical", "horizontal", and derivatives thereof shall relate to the invention as oriented in FIG. 1. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification, are simply exemplary

embodiments of the inventive concepts defined in the appended claims. Hence, specific dimensions and other physical characteristics relating to the embodiments disclosed herein are not to be considered as limiting, unless the claims expressly state otherwise.

Piston driven cylinders, such as the exemplary cylinder assembly 100, which can be a hydraulic or pneumatic cylinder, illustrated in FIG. 1, are generally operated by high pressure air or hydraulic fluid. The term hydraulic cylinder is used in the meaning of using either a fluid, such as hydraulic fluid, or a gas, such as pressurized air. The exemplary hydraulic cylinder assembly 100 is fabricated having a cylinder head 112 extending between a cylinder barrel 110 and a cylinder base 114. The cylinder barrel 110 is fabricated of a tubular material suitable for retaining a pressurized medium. The cylinder barrel 110 is enclosed with the inclusion of cylinder head 112 at a head end of the cylinder head 112 and a cylinder base 114 at a base end of the cylinder head 112. A base seal 116 is combined with the cylinder base 114 to provide a seal at the base end of the cylinder barrel 110. A bushing 136 is combined with the cylinder head 112 to provide a seal at the head end of the cylinder barrel 110. A sealed chamber 118 is created within an interior of the hydraulic cylinder assembly 100. A piston 120 is slideably assembled within the sealed chamber 118. The piston 120 is fabricated having an exterior shape and peripheral size that is substantially equal to an interior shape and peripheral size of the sealed chamber 118. At least one piston seal and rings 122 is provided about a peripheral edge of the piston 120 forming a fluid seal between the interior periphery of the sealed chamber 118 and the exterior periphery of the piston 120, while enabling motion of the piston 120 along a longitudinal axis thereof. A piston tie rod 130 is attached to the piston 120 by a piston rod attachment 132. The bushing 136 provides a sealed passageway for the piston tie rod 130 to exit from within the sealed chamber 118 for engagement with other mechanically operative members. The piston tie rod 130 slideably passes through a bushing aperture 138 of the bushing 136.

The components used in an outer structure of the hydraulic cylinder assembly 100 can be fabricated of a metallic material, a composite material, a polymer, a plastic material, and the like. The bushing 136 can be fabricated of brass, a polymer, and the like. The piston tie rod 130 is commonly fabricated of a solid or tubular metallic material, but could be manufactured of any other material, such as a composite, a plastic, and the like, suitable for the application.

An operational medium is utilized to operate the hydraulic cylinder assembly 100. The operational medium can be a pressurized gas (air, nitrogen, and the like) or a fluid (such as hydraulic fluid, oil, water, and the like). Operation of the hydraulic cylinder assembly 100 is completed by adjusting pressure of an operational medium within one or both sections of the sealed chamber 118 as segmented by the position of the piston 120. The change in pressure applies a force to the respective side of the piston 120. The resulting force causes the piston 120 to slideably move within the sealed chamber 118, in turn causing the piston tie rod 130 to move accordingly. A first pressure may be applied through a connection 150 suitable for, for example, hydraulic oil, located through the bushing 136 (as shown), the cylinder head 112, or any other reasonable location within a head side of the piston 120. Pressure applied to the operational medium on the head side of the piston 120 drives the piston 120 towards the base side of the sealed chamber 118. This draws the piston tie rod 130 inward into the sealed chamber 118. A second pressure may be applied through a connection 154 suitable for, for example, high pressure air, located through the base seal 116 (as shown), the cylinder base 114, or any other reasonable location within a base side of the piston 120. Pressure applied to the operational medium on the base side of the piston 120 drives the piston 120 towards the head side of the sealed chamber 118. This drives the piston tie rod 130 outward from the sealed chamber 118. The piston tie rod 130 may be coupled to the mechanically operative member by a tailrod 134 or any other coupling interface. A number of factors can contribute to the overall force exerted by the piston tie rod 130 upon a mechanically operative member coupled thereto. Examples of several factors include the surface area of a face of the piston 120, the pressure of the operational medium, the compressive properties of the operational medium, the maximum allowable pressure contained within the sealed chamber 118, and the like. The bushing 136 is commonly fabricated of a material designed to wear at a quicker rate than the piston tie rod 130, thus governing the servicing of the hydraulic cylinder assembly 100. The concern is wear of the bushing aperture 138 during use.

Motions of the piston tie rod 130 passing through the bushing aperture 138 causes wear on the bushing aperture 138. Friction, non-linear motion, non-axial forces, and the like can contribute to degradation of the condition of the bushing aperture 138 of the bushing 136.

A bushing condition monitoring ring 200 can be integrated into the bushing 136 as illustrated in FIGS. 2 and 3. The bushing condition monitoring ring 200 includes a series of laminated annular sections comprising thin layers of a thin dielectric base material 210, 212, 214, 216 and layers of electrically conductive material 220, 222, 224. Each layer of electrically conductive material 220, 222, 224 is disposed between adjacent thin dielectric base material layers 210, 212, 214, 216. The electrically conductive material 220, 222, 224 can be any electrically conductive material, including copper foil, copper, gold, gold plated nickel, silver, and the like. The exemplary embodiment presented in the cross section illustrated in FIG. 4 utilizes electrically conductive material 220, 222, 224 fabricated of a copper foil having a preferred thickness of approximately 0.032mm or 32um. The dielectric base material 210, 212, 214, 216 can be fabricated of any flexible plastic substrate, including polyimide, Polyether ether ketone (commonly referred to as PEEK), transparent non-conductive polyester film, and the like. The dielectric base material is preferably fabricated of a thin material, having a preferred thickness of approximately 0.05mm or 50um. The dielectric base material 210, 212, 214, 216 ensures against short circuits between each adjacent layer of electrically conductive material 220, 222, 224. The interior diameter of the bushing condition monitoring ring 200 is preferably the same diameter as the diameter of the bushing aperture 138.

An electrical pathway is provided from each electrically conductive layer 220, 222, 224 to a monitoring device by an electrically conductive interface 240, 242, 244. An optional non-conductive layer 230, 232, 234, 236 can be provided to ensure against shorting adjacent electrically conductive layers 220, 222, 224 or shorting any of the electrically conductive layers 220, 222, 224 with any another electrically conductive component located proximate the bundle of electrically conductive interfaces 240, 242, 244. The exemplary electrically conductive interfaces 240, 242, 244 are presented as foil layers. It is understood that the electrically conductive interfaces 240, 242, 244 may be any electrically conductive material provided in any reasonable form factor for conveyance of an electrical charge from the respective electrically conductive annular ring 220, 222, 224, including individual wires, a bundle of wires, a flexible circuit, a ribbon cable, and the like.

The bushing condition monitoring ring 200 is integrated into a monitoring system shown in an exemplary block diagram illustrated in FIG. 5. The series of electrically conductive interfaces 240, 242, 244 are provided in electrical communication with a processing device 400 by an electrically conductive carrier. The bushing condition monitoring ring 200 is provided in electrical communication with the processing device 400 via the series of electrically conductive interfaces 240, 242, 244. The processing device 400 includes common digital data processing components, include a motherboard, at least one microprocessor, memory, a data recording device, digital instructions (such as software, firmware, and the like), input/output controllers, data communication devices, and the like. A user input device 420 and a user output device 420 are connected in signal communication to the processing device 400 through the input/output controllers. The processor monitors the status of the bushing condition monitoring ring 200 to determine the condition of the bushing 136. The monitoring can be continuous, accomplished at predetermined time intervals, or manually requested. The system monitors electrical characteristics of the bushing condition monitoring ring 200 to determine the condition of the bushing 136. The electrical characteristics can include electrical contact of a layer with the piston, capacitance between layers, conductivity, and the like. The electrically conductive annular rings 220, 222, 224 can be etched to create inductive paths, where the electrical characteristics can utilize inductance.

The bushing condition monitoring ring 200 can be modified by separating the electrically conductive rings 320, 322, 324 into electrical pathways by including an electrically non-conductive section 350, 352, 354 forming a bushing condition monitoring ring 300 as illustrated in FIG. 6. The electrically non-conductive section 350, 352, 354 segments each respective electrically conductive ring 320, 322, 324 into a single electrical pathway as follows: Each electrically non-conductive section 350, 352, 354 bisects the respective electrically conductive interface 340, 342, 344 creating a circuit capable of being monitored using continuity about each respective electrically conductive ring 320, 322, 324. The non-conductive annular ring layer 336 is partially sectioned in the illustration to expose the entire electrically non-conductive section 354 of the electrically conductive interface 344 illustrating the bisecting arrangement thereof. A source electrically conductive pathway provides a current to a first side of the electrically conductive material 320, 322, 324, along the annular ring, and returns through a second side of the electrically conductive material 320, 322, 324, passing onto a return conductive pathway. The single electrical pathway retains continuity until a portion of the thickness of the material is removed causing an open circuit. The system would monitor continuity about each electrically conductive ring 320, 322, 324. The system would identify wear of each ring by a change in the resistance exhibited by the respective electrically conductive ring 320, 322, 324, with an open circuit indicating that the respective electrically conductive ring 320, 322, 324 has been worn through, giving an indication of the amount of wear.

The exemplary embodiment presents a configuration initiating with a non- conductive layer 216, 316 defining the interior surface of the bushing condition monitoring ring 200, 300. It is understood that the bushing condition monitoring ring 200, 300 can be fabricated omitting the thin dielectric base material layers 216, 316 where the inner most electrically conductive annular ring 224, 324 defines the interior surface. The outer surface of the bushing condition monitoring ring 200, 300 can be modified in a similar manner.

The exemplary monitoring ring receiving groove 250 is shown located proximate one end of the bushing 136. It is understood that the monitoring ring receiving groove 250 can be formed at either end of the bushing aperture 138, formed at both ends of the bushing aperture 138 for integrating a bushing condition monitoring ring 200, 300 at each end thereof, or formed along a central location of the bushing aperture 138. In a configuration where the monitoring ring receiving groove 250 is centrally formed, the assembly would additionally include a filler annular ring extending from the exposed edge of the bushing condition monitoring ring 200, 300 to the respective edge of the bushing.

Since many modifications, variations, and changes in detail can be made to the described preferred embodiments of the invention, it is intended that all matters in the foregoing description and shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense. Thus, the scope of the invention should be determined by the appended claims and their legal equivalence.

Ref. No. Description

100 cylinder assembly 100, such as a hydraulic cylinder assembly

110 cylinder barrel 1 10

112 cylinder head 1 12

114 cylinder base 1 14

116 base seal 1 16

118 sealed chamber 1 18

120 piston 120

122 piston seal and rings 122

130 piston tierod 130

132 piston rod attachment 132

134 tailrod 134

136 bushing 136

138 bushing aperture 138

150 connection 150, such as a hydraulic oil connection

154 connection 154, such as a high pressure air connection

200 monitoring ring 200

210 thin dielectric base material layers 210

212 thin dielectric base material layers 212

214 thin dielectric base material layers 214

216 thin dielectric base material layers 216

220 conductive material 220

222 conductive material 222

224 conductive material 224

230 non-conductive annular ring layer 230

232 non-conductive annular ring layer 232

234 non-conductive annular ring layer 234

236 non-conductive annular ring layer 236

240 conductive interface 240

242 conductive interface 242

244 conductive interface 244

250 monitoring ring receiving groove 250

400 processing device 400

410 user input device 410

420 user output device 420

350 electrically non-conductive section 350

352 electrically non-conductive section 352

354 electrically non-conductive section 354

300 monitoring ring 300