Patent Application
20140352527
The present invention relates generally to linear actuators, and more particularly to a linear actuator having a trapezoidal bearing block operably coupled between a shaft and housing for preventing rotation of the shaft relative to the housing.
In many manufacturing processes, individual sheet metal components are fabricated with locating holes. Locating pins extend through these holes to hold two or more sheet metal components in position relative to each other and to the resultant sheet metal assembly during welding processes. Accordingly, accurate positioning of the locating pins is typically necessary to ensure consistency in the sheet metal assembly.
Stationary locating pins may be fixed to a frame of the associated manufacturing equipment for locating the individual sheet metal components. However, in many manufacturing situations, the locating pins must be retracted from the completed sheet metal assembly so that it can progress to the next operation. In order to retract the locating pin(s), the locating pin(s) are often mounted on a linear actuator.
A linear actuator typically comprises a housing which defines an internal bore and a piston-rod assembly which moves within the internal bore in response to fluid pressure. One end of the rod is attached to the piston, and the other end of the rod extends beyond the housing, wherein pilot holes, flats and/or threaded passages are provided on the rod for securing a locating pin thereto.
During locating and/or welding processes, it is often important that the piston-rod assembly not rotate relative to the housing. Such non-rotation is important for ensuring that the working position of the locating pin is reliable and repeatable. For example, over repeated use, wear may occur on the locating pin, wherein the wear is associated with a particular area of the sheet metal component(s). If the locating pin were to be permitted to rotate with respect to the housing of the linear actuator, the locating pin could wear unequally, and the resulting positioning of the sheet metal component(s) can vary based on the rotational position of the locating pin. Further, rotational issues are magnified when it is necessary for a locating pin to be attached to an actuator with an offset, wherein the offset allows the locating pin to fit or be actuated around another part of the equipment during sheet metal working operations.
One technique traditionally used to prevent rotation of a piston-rod assembly in a linear actuator is to provide the rod with a corresponding bearing surface of the internal bore having a rotation-preventing cross-sectional geometry. For example, the rod/bearing surface can be fabricated having a square cross-sectional geometry.
One common example is illustrated in
However, such polygonal arrangements are difficult to fabricate, in that consistently matching the square bearing 30 to a square shaft 15 in a high production environment is technically challenging and/or expensive to achieve. Further, even if fabrication issues are ignored, such polygonal arrangements tend to present wear problems. Specifically, whenever torque is applied to the square shaft 15 (such as from an offset locating pin) the four corners 35 of the shaft will continuously contact the bearing surface 40, thereby making these minimal areas of the shaft highly susceptible to wear. Furthermore, replacement of the worn parts typically requires disassembly of the housing components, disassembly of the piston-rod assembly, and/or replacement of the entire rod, thus deleteriously affecting production and costs associated with the linear actuator.
Another rotation-preventing technique used to prevent rotation of the piston-rod assembly in a linear actuator is to provide a round anti-rotation member coupled to the rod with a corresponding bearing slot defined in the housing, wherein the anti-rotation member travels within the slot, therein preventing rotation of the piston-rod assembly with respect to the housing. However, the inventors appreciate that wear can still occur on either of the anti-rotation member and/or slot, therein necessitating removal and replacement of the anti-rotation member and/or housing.
The present invention overcomes the limitations of the prior art by providing a robust linear actuator operable to provide consistent positioning of workpieces Consequently, the following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is intended to neither identify key or critical elements of the invention nor delineate the scope of the invention. Its purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.
The present disclosure is generally directed toward a linear actuator having a robust anti-rotation mechanism. The linear actuator comprises a housing having a bore therethrough, therein defining an axis. A shaft is in sliding engagement with at least a first portion of the bore, wherein a piston is further coupled to the shaft. The first portion of the bore, for example, has a circular cross-section when viewed along the axis. The piston is in further sliding engagement with a second portion of the bore.
In accordance with one exemplary aspect, a novel anti-rotation apparatus is provided, wherein the anti-rotation apparatus comprises an elongate slot defined in the housing and a bearing block coupled to the shaft via an attachment member. The elongate slot, for example, is axially offset from the bore. Opposing sidewalls of the elongate slot extend parallel to the axis, wherein the opposing sidewalls are generally V-shaped when viewed along the axis. Opposing sides of the bearing block are further generally V-shaped when viewed along the axis, wherein the opposing sides of the bearing block respectively slidingly engage the opposing sidewalls of the elongate slot. The sliding engagement between the opposing sides of the bearing block and opposing sidewalls of the elongate slot therein generally prevent a rotation of the shaft about the axis.
According to one example, the bearing block has a trapezoidal geometry when viewed along the axis, wherein the opposing sides of the bearing block are respectively offset from a plane perpendicular to the axis by a respective predetermined angle. Further, the opposing sidewalls of the elongate slot are respectively offset from the plane perpendicular to the axis by the same respective predetermined angle. In one example, the opposing sides of the bearing block are equally offset from the plane perpendicular to the axis. Alternatively, the respective predetermined angle can differ between the opposing sides of the bearing block. In another example, the respective predetermined angle is selected from a range between zero and fifteen degrees from the plane perpendicular to the axis.
The bearing block, for example, is formed as an extrusion, wherein the extrusion generally defines the opposing sides of the bearing block. As such, efficiencies in manufacturing of the bearing block can be achieved over other methods, as the respective predetermined angles of the opposing sides of the bearing block can be closely, yet inexpensively maintained.
In accordance with another aspect, the anti-rotation apparatus, for example, can further comprise one or more friction-reducing coatings disposed on one or more of the opposing sides of the bearing block and the opposing sidewalls of the elongate slot. In one example, the one or more friction-reducing coatings comprise an electroless nickel coating formed on the opposing sides of the bearing block. In other examples, the one or more friction-reducing coatings comprise one or more of grease, oil, graphite, and an ultra-high molecular weight film.
The bearing block, for example, further comprises a hole extending generally perpendicular to the axis, wherein the attachment member is configured to extend through the hole and to selectively couple the bearing block to the shaft. In one example, the shaft comprises a threaded hole extending generally perpendicular to the axis into the shaft. Accordingly, the attachment member comprises a bolt having a head and a threaded portion, wherein the threaded portion of the bolt threadingly engages the threaded hole in the shaft. As such, the head of the bolt forces the bearing block toward the shaft, therein engaging the opposing sides of the bearing block with the opposing sidewalls of the elongate slot. The attachment member, for example, provides a selective engagement force between the opposing sides of the bearing block and the opposing sidewalls of the elongate slot.
In yet another example, a sensor assembly is provided, wherein the sensor assembly is configured to sense a position of the anti-rotation apparatus along the axis.
Thus, to the accomplishment of the foregoing and related ends, the disclosure comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.
The present disclosure will be described with reference to the drawings wherein like reference numerals are used to refer to like elements throughout. It should be understood that the description of these aspects are merely illustrative and that they should not be taken in a limiting sense. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. It will be evident to one skilled in the art, however, that the present disclosure may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to facilitate description of the present disclosure.
Referring now to the Figures, in accordance with the present disclosure,
In accordance with one exemplary aspect, a shaft 118 illustrated in
Referring to
In accordance with the disclosure, the anti-rotation apparatus 124 further comprises , a bearing block 134 operably coupled to the shaft 118 via an attachment member 136, wherein, as illustrated in
In the example illustrated in
In accordance with another example, as illustrated in
The attachment member 136, for example, provides a selective engagement force between the opposing sides 138, 140 of the bearing block 134 and the opposing sidewalls 130, 132 of the elongate slot 126. The engagement force, for example, can be adjusted based on desired anti-rotation of the shaft 118. Further, should the bearing block 134 be subject to significant wear, the attachment member 136 can be advantageously tightened, therein re-establishing the desired engagement force. The bearing block 134 may be further selectively removably coupled to the shaft 118 via the attachment member 136, wherein the bearing block may be inspected, replaced, or otherwise removed.
The bearing block 134 of the anti-rotation apparatus 124 of
In one example, the bearing block 134 is formed as an extrusion, wherein the extrusion generally defines the opposing sides 138, 140 of the bearing block. Since angular surfaces (e.g., the opposing sides 138, 140 of the bearing block) can be produced accurately and inexpensively via extrusion, cost savings can be attained over conventional machining. Furthermore, since the angular orientation of the opposing sides 138, 140 is the only dimension needing relative precision, a height 158 of the bearing block can vary and is non-critical, as the height can be compensated for via the attachment member 136.
According to yet another exemplary aspect, the anti-rotation apparatus 124 of
In accordance with still another example, the linear actuator 100 further comprise a sensor assembly 160, as illustrated in
Accordingly, the present disclosure provides a linear actuator having a robust anti-rotation mechanism, wherein the anti-rotation mechanism provides accurate positioning of the shaft. Further, the anti-rotation mechanism can be inexpensively implemented, and inspection and replacement of the various components associated therewith can be readily performed. Previous rotation-preventing techniques involving a round anti-rotation member coupled to a shaft with a corresponding bearing slot defined in the housing lead to significant wear on either of the anti-rotation member and/or slot, therein necessitating removal and replacement of the anti-rotation member and/or housing. The present disclosure advantageously provides an anti-rotation apparatus 124 wherein the bearing block 134 can be simply tightened against the elongate slot 126 via the attachment member 136, should the bearing block experience wear. Thus, the present invention provides a significant advantage over previous linear actuators, as the need to remove and replace of anti-rotation components is significantly reduced.
Although the disclosure has been shown and described with respect to certain aspects, equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described components (systems, devices, assemblies, etc.), the terms used to describe such components are intended to correspond, unless otherwise indicated, to any component which performs the specified function of the described component (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure that performs the function in the herein illustrated exemplary aspects of the disclosure. In addition, while a particular feature of the invention may have been disclosed with respect to only one of several aspects, such feature may be combined with one or more other features of the other aspects as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the term “includes” is used in either the detailed description or the claims, such term is intended to be inclusive in a manner similar to the term “comprising.”
