GB2411202A - Position sensing unit with resilient / detent fixing leg - Google Patents

Abstract

A sensor unit for a linear actuator or piston and cylinder assembly having on the exterior of the cylinder an undercut groove to receive such sensor unit, comprises an elongate body portion 10 Fig 1 accommodating a sensor, the body portion 10 having at one end a pair of diverging resilient legs 30. Each leg 30 has an abutment surface at its free end, for engagement with the undercut region of such groove. As the opposite end of body portion 10, there is provided a releasable catch 32, 33 for retaining said opposite end in such undercut groove, such that the sensor unit can be released from such an undercut groove by releasing said catch 32, 33, lifting the end with the catch 32, 33 from the groove and rotating the sensor unit about the one end with the legs 30, about an axis transverse to the direction of elongation of the body portion 10, to an almost inverted position in which the resilient legs 30 diverge downwardly in the groove and pulling the end with the legs upwardly out of the groove.

Description

241 1 202 THIS INVENTION relates to position sensors for piston and

cylinder assemblies, also known as linear actuators, and to a method of fitting and removing such sensors.

Where piston and cylinder assemblies or linear actuators are used to perform operations automatically, it is frequently necessary to provide electrical signals to control circuitry to indicate when the piston in a piston and cylinder assembly has reached a particular position. In some known arrangements, such signals are provided by a sensor unit, incorporating an electrical sensor, such as a reed switch, or a Hall effect device, fitted in a groove which extends longitudinally along the cylinder or along a holder or casing for such cylinder, the arrangement being such that the position of the linear actuator at which the respective signal is produced can be adjusted by sliding the sensor unit along the groove. In such an arrangement, the groove may be undercut, in the sense that the mouth or outer part of the groove is narrower than an interior region, so that the sensor unit, having a part received in that interior region of the groove and too wide to pass through the narrower part or mouth of the groove is held captive within the groove until a dedicated extraction procedure is applied.

It is an object of the present invention, in one of its aspects, to provide an improved sensor unit for the purpose outlined above, and for which the installation and extraction procedures are relatively simple and which nevertheless provides for secure retention of the sensor unit.

It is a further object of the invention to provide such a sensor unit which can be installed and removed from a sensor groove in a cylinder or cylinder holder of a linear actuator without any need to slide it through an open end of such groove, whereby the ends of such a groove can be occluded without interfering with the facility with which the sensor can be fitted and removed.

According to the invention, in one aspect, there is provided a sensor unit for a linear actuator or piston and cylinder assembly having on the exterior of the cylinder an undercut groove to receive such sensor unit, the sensor unit comprising an elongate body portion accommodating a sensor such as a reed switch, the body portion having a first surface, herein referred to as the outer surface, and a second, opposite surface, herein referred to as the inner surface, said elongate body portion having at one end thereof a pair of resilient legs, each said leg being connected with said body portion via an inner end of the leg adjacent said inner surface, and extending from said inner end towards the location of said outer surface, each said leg having an abutment surface located somewhat closer to said inner surface than is said outer surface, for engagement with the undercut region of such groove, and said legs diverging from one another from their inner ends so that the surfaces of said legs facing away from one another are spaced by a distance substantially corresponding to the width of said body portion at their inner ends and are spaced apart by a significantly greater distance at the level of said abutment surfaces, and wherein, at the opposite end of said body portion, there is provided releasable catch means for retaining said opposite end in such undercut groove.

According to another aspect of the invention there is provided the combination of a piston and cylinder assembly or linear actuator and a sensor unit according to the first mentioned aspect of the invention, the cylinder of the piston and cylinder assembly, or a casing or holder for such cylinder having on its exterior a groove which extends longitudinally along the cylinder and which is undercut in the sense that a mouth of the groove, opening onto the exterior of the cylinder, or of said casing or holder, is narrower than an interior part of said groove, whereby respective shoulders are provided within the groove, on either side of the groove, facing the bottom of the groove, said shoulders being formed by the transitions between the interior part of the groove and the mouth of the groove, the sensor unit being fitted within said groove, with the region of said body portion providing said outer surface lying within said mouth, and with said legs and said first part of said arm lying within said interior part of said groove, said abutment surfaces of said legs and said abutment surface or detent of said arm opposing respective said shoulders of said groove.

An embodiment of the invention is described below by way of example and with reference to the accompanying drawings in which: Figure l is a perspective view of a sensor unit embodying the invention; Figure 2 is a plan view of the sensor of Figure 1; Figure 3 is a side view of the sensor of Figure 1; Figure 4 is an end view of the sensor unit; Figure 5 is a view from the opposite end of the sensor unit; Figure 6 shows schematically the sensor unit about to be installed in an undercut groove in the cylinder wall or cylinder casing or holder of a piston and cylinder unit or linear actuator (shown only fragmentarily); Figure 7 is a view corresponding to Figure 6 but showing the sensor unit in place; Figure 8 is a view corresponding to Figure 7 but viewed from the opposite end of the sensor unit; and Figures 9 to 14 are perspective views illustrating installation and removal of the sensor unit.

Referring to Figures 1 to 6 there is illustrated a sensor unit embodying the invention and which comprises an electrical sensor (not shown), such a reed switch or a Hall effect sensor, incorporated in an elongate plastics body portion l O which, over most of its length, is of substantially constant rectangular cross- section, (such cross-section being perpendicular to the direction of greatest extension of the body portion). At one end of the elongate body portion 10 is provided a pair of resilient legs 30, whilst at the opposite end there is provided a retaining means 32.

In use of the device, an electrical lead (not shown) is connected thereto for connecting the device to monitoring or control circuitry (not shown), such lead, for example, extending from one end of the sensor unit or from the outer surface thereof. Referring to Figures 6 to 8, the sensor unit is intended to be fitted in an undercut groove or channel 40 in the wall of the cylinder or cylinder casing or holder 44 of a piston and cylinder unit (not shown otherwise in Figures 6 to 8). The member 44 may, as illustrated in Figures 9 to 14, take the form of an extruded body which forms a carrier and external support for a cylinder proper (not shown) of a pneumatic or hydraulic piston cylinder unit (not shown). The groove 40 extends longitudinally - i.e. in the direction in which the piston of the piston and cylinder assembly will move, and has the cross-sectional form best shown in Figure 6. Thus, the groove or channel 40 may have, as shown, a generally rectangular form with a flat bottom wall 42, side walls 40b perpendicular to the wall 40a and spaced apart from one another by a first distance, the groove 40 having a restricted mouth defined between lateral ledges or flanges 40c which are spaced apart from one another by a second distance and which define respective shoulders or abutment faces 40d extending from the upper edges of the side walls 40b and facing towards the bottom wall 40a. The groove or channel 40 may have some form other than rectangular in cross-section, provided that it affords lateral ledges or flanges such as flanges 40c at the mouth of the groove. Thus, the groove may, for example be generally trapezoidal in cross-section, with the opposing walls 40b being inclined with respect to each other, rather than parallel. The body portion 10 of the sensor unit has an upper or outer surface 32a and a lower or inner surface 32b, and side walls 32c substantially perpendicular with the inner and outer surfaces 32b, 32a. The width of the body portion 10 of the sensor unit, as measured between the faces 32c, is only slightly less than said second distance, i.e., than the spacing between the opposing edge faces of the flanges 40c, so l O that when the sensor unit is installed, as illustrated in Figure 7, the body portion fits snugly in the mouth of the groove, between these flanges 40c. The legs 30 extend upwardly from a longitudinal extension 50 of the body portion 10 at one end thereof, the lower surface of extension 50 being substantially co- planar with the inner surface of the body portion 10 but the extension 50 being of significantly lesser depth than the body portion 10. In the unstressed state, as shown in Figure 6, the legs 30 diverge upwardly and outwardly away from the inner surface 32b in the direction generally towards the plane of the upper surface 32a, but the legs 30 stop significantly short of that upper surface, so that, in the installed position, as shown in Figure 7, the upper ends of the legs 30 form abutment surfaces which oppose and co-operate with the downwardly directed shoulders 40d of the flanges 40c, to hold the sensor unit in place.

At the opposite end of the body portion, the retaining means 32 comprises a resilient arm 33 which is connected at its lower, inner end with a further longitudinal extension 34 from the rectangular body portion but is otherwise free to flex about its connection with this extension. The extension 34, in the embodiment shown, comprises an approximately cylindrical stub extending longitudinally from the respective end of the body portion 10. A socket for receipt of an electrical connector may extend longitudinally through this stub 34. Normally, however, the reed switch or other sensor within the body portion 10 will be connected with a cable (not shown) extending through a longitudinal bore in stub 34 and thence, from the end of the unit provided by stub 34, to a monitoring facility, not shown, the reed switch or other sensor and the adjoining part of said cable being potted with epoxy within the body portion 10.

The arm 33 comprises a first or inner portion extending from the connection of the lower end of the arm with the extension 34 to a detent portion 35 providing a face or shoulder facing the face or shoulder 40d on the respective side of the groove 40, the arm 33 having a further or outer portion 36 extending from the location of the detent 35, through the mouth of the groove and terminating substantially flush with the upper surface 32a of the body portion. This further portion 36 serves as an operating portion by which the arm 33 may be deflected laterally, away from the respective edge of the groove 40, for release of the sensor unit, as described below.

The end of the body portion 10 carrying the legs 30 has a screw threaded through bore extending from the outer to the inner surface and which accommodates a grub screw which can be screwed up to lock the sensor unit in a desired longitudinal position in the groove, once it has been adjusted to the desired position by sliding longitudinally along the groove.

Figure 9 illustrates the fitting of the sensor unit. To fit the unit it is simply positioned with the lower inner surface 32b facing towards the bottom 40a of the groove, as shown in Figures 6 and 9, with the body portion 10 aligned with the groove 40 and the whole unit is pushed, in the direction indicated by the arrow in Figures 6 and 9, into the groove 40, the legs 30 deflecting resiliently laterally during such insertion, to pass the flanges 40c.

Once the sensor unit has been fully inserted (see Figure 7 and Figure 10), the legs 30 spring outwardly behind the flanges 40c and the arm 33 springs laterally towards the adjacent side wall of the groove 40 as the detent 35 thereon passes the adjacent flange 40c. Thereafter, movement of the sensor unit from the groove by a reversal of the movement described is prevented by abutment with the ends of the legs 30 and the detent on arm 33 with the undersides of the lips of the groove. The sensor unit can then be slid longitudinally to the desired position along the groove and the grub screw 37 can then be tightened to force the inner end of the grub screw against the inner bottom wall of the groove and conversely to force the free ends of legs 30 against the shoulders 40d afforded by the flanges 40c, whereby the sensor unit is held firmly in place.

In order to remove the sensor unit, when desired, from the groove, the grub screw 37 is slackened, the arm 33 is deflected away from the adjacent side wall of the groove, e.g. by means of a pointed instrument, and simultaneously the end of the unit bearing the arm 33 is swung upwardly out of the groove as shown in Figure 11. As shown in Figures 12 and 13, this swinging movement of the unit is continued until the unit is partially inverted (Figure 13), at which point the unit can be pulled upwards since the directions in which the legs 30 now diverge are such as to allow them to be deflected towards each other by a camming action with the flanges 40c of the groove as the unit is lifted from the groove.

When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims (6)

1. A sensor unit for a linear actuator or piston and cylinder assembly having on the exterior of the cylinder an undercut groove to receive such sensor unit, the sensor unit comprising an elongate body portion accommodating a sensor such as a reed switch, the body portion having a first surface, herein referred to as the outer surface, and a second, opposite surface, herein referred to as the inner surface, said elongate body portion having at one end thereof a pair of resilient legs, each said leg being connected with said body portion via an inner end of the leg adjacent said inner surface, and extending from said inner end towards the location of said outer surface, each said leg having an abutment surface located somewhat closer to said inner surface than is said outer surface, for engagement with the undercut region of such groove, and said legs diverging from one another from their inner ends so that the surfaces of said legs facing away from one another are spaced by a distance substantially corresponding to the width of said body portion at their inner ends and are spaced apart by a significantly greater distance at the level of said abutment surfaces, and wherein, at the opposite end of said body portion, there is provided releasable catch means for retaining said opposite end in such undercut groove, whereby the sensor unit can be released from such an undercut groove by releasing said catch means, lifting said opposite end from said groove and rotating the sensor unit about said one end, about an axis transverse to the direction of elongation of said body portion, to a position in which said resilient legs diverge downwardly in the groove rather than upwardly, and pulling said one end upwardly from the groove.

2. A sensor unit according to Claim 1, wherein said releasable catch means comprises a resilient arm, on one side of said body portion and having an inner end connected with said body portion at a location adjacent said inner surface, said arm extending away from said inner surface, in the general direction of said outer surface of said body portion, with a first part of said arm inclining away from the centre line of said body portion with increasing distance from said inner end of said arm, and a further part of said arm extending from said first part, and an abutment surface or detent being provided on said arm at the junction between said first part and said second part.

3. A sensor unit according to claim 1 or claim 2 wherein said abutment surfaced of said legs are provided by free ends of said legs.

4. A sensor unit according to any of claims 1 to 3 including means at or adjacent said one end of said body portion and capable of being extended from said inner surface in the direction away from said outer surface, for engagement with the bottom of such groove when the sensor unit displaced in such groove.

5. A sensor unit according to claim 4 wherein said means comprises a screw, screw threadedly engaged in said body portion.

6. The combination of a piston and cylinder assembly or linear actuator and a sensor unit according to any of claims 1 to 5, the cylinder of the piston and cylinder assembly, or a casing or holder for such cylinder having on its exterior a groove which extends longitudinally along the cylinder and which is undercut in the sense that a mouth of the groove, opening onto the exterior of the cylinder, or of said casing or holder, is narrower than an interior part of said groove, whereby respective shoulders are provided within the groove, on either side of the groove, facing the bottom of the groove, said shoulders being formed by the transitions between the interior part of the groove and the mouth of the groove, the sensor unit being fitted within said groove, with the region of said body portion providing said outer surface lying within said mouth, and with said legs and said first part of said arm lying within said interior part of said groove, said abutment surfaces of said legs and said abutment surface or detent of said arm opposing respective said shoulders of said groove.