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Electro-magnetic clamp for gripping a shaftRelated Patent Categories: Brakes, RodElectro-magnetic clamp for gripping a shaft description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060196737, Electro-magnetic clamp for gripping a shaft. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] The invention relates to a releasable clamp for gripping a shaft, for holding a component in a selected fixed position relative to a shaft. BACKGROUND OF THE INVENTION [0002] Mechanical and electro-mechanical devices for holding a component in position in relation to a shaft have applications in many fields. For example, an optical device for measuring a patient's eyes must be precisely positioned in relation to the patient, requiring that the device be freely moveable along a shaft until it reaches the correct position, at which time it must be clamped to the shaft in a releasable fashion but which holds it firmly in place. Numerous other applications exist for a clamp which releasably holds a component in a fixed position along a shaft, but which may be readily released to permit either sliding or rotary movement or both. Existing clamps may comprise a clamp body which supports a pair of angled plates having an aperture therethrough, the plates being pivotable about one end such that a shaft passing through the plates may slide or rotate freely therethrough when the plates are steeply angled relative to the shaft, but is prevented from moving when the plates are more shallowly angled. However, this type of system is subject to a high level of wear and other drawbacks. Other systems have been proposed, all of which involve a relatively high degree of complexity. There is a need for a relatively simple, effective clamp suitable for actuation by electromagnetic means such as a solenoid motor. [0003] A variety of mechanical clamping systems have been proposed for releasably fixing a component to a shaft in a manner such that the component may be readily re-positioned on the shaft. For example, U.S. Pat. No. 5,052,842 to Janatka discloses a slotted hub having a central bore for receiving a shaft, with a screw to tighten the collar around the shaft for locking engagement. In a somewhat similar fashion, U.S. Pat. No. 4,142,811 to Burnham discloses a hub having a central bore, with the hub being perforated with threaded openings to receive a plurality of screws which when tightened directly or indirectly contact a shaft extending through the bore. Upon tightening the screws, contact is made with the shaft thereby locking the shaft relative to the hub. [0004] Another type of locking system is disclosed in U.S. Pat. No. 4,893,810, the commercial embodiment of which is the "Grip Fast.TM." collar, and is specifically intended for locking athletic weights to a barbell shaft. The collar comprises concentric inner and outer sleeves, the inner sleeve having a plurality of openings to receive bearings extending partway through the openings. A plurality of wedges are positioned to contact the bearings, such that when the outer sleeve is aligned relative to the inner sleeve, the bearings are wedged inwardly and extend through the inner sleeve so as to contact and lock the shaft in position. Axial displacement of the sleeves relative to each other permits the bearings to retract, thereby releasing the shaft. The inner and outer shafts are spring biased relative to each other so as to maintain the locked position until the user retracts the outer sleeve. Similar locking systems are disclosed in U.S. Pat. Nos. 4,395,051 and 4,453,449. SUMMARY OF THE INVENTION [0005] An object of the invention is to provide an improved clamp for releasably fastening a component along a shaft, such that when released the component may be rotated or slid along the shaft, or both rotated and slideably displaced, and which when engaged, prevents either axial or rotary movement, or both, relative to the shaft. A further embodiment is to provide such a clamp which may be actuated by an electromagnetic component such as a solenoid. [0006] In one aspect, the invention relates to a clamp for gripping an elongate shaft comprising a clamp body having a bore for slideably receiving the shaft. Within the body is provided at least two opposing shaft grippers coaxial with the bore for selectively gripping the shaft. The shaft grippers are of the type comprising a pair of concentric sleeves displaceable relative to each other, whereby when aligned the outer sleeve urges bearings or other contact members to press against the shaft so as to firmly grip the shaft to prevent movement relative to the gripper, and when displaced the contact members retract to release the shaft. Alternatively, the gripping may occur when the sleeves are displaced relative to each other and release when aligned. Typically, such grippers are most effective only in a single direction, since a retraction of the shaft in a first direction cooperates with the wedging action of the contact members, while retraction in an opposed direction will release the gripper. Thus, in order to prevent shaft slippage in either axial direction, it is desirable to provide a pair of grippers within the clamp body, aligned along the shaft and in opposing directions whereby they may be simultaneously actuated for gripping or releasing the shaft. [0007] In order to actuate the grippers, a pair of opposing plungers is provided for contacting the inner sleeve of each gripper so as to urge the inner sleeve inwardly towards the centre of the body, so as to release the shaft. The grippers are recessed into the clamp body. The outer sleeve of each gripper is fixed in position, by abutting against a shoulder within the interior of the clamp body. The inner sleeve can move axially within a pocket inboard of the shoulder. The plungers are each operatively connected to an arm extending outwardly from the body, the arm mounted to the body for sliding movement in a direction axial to the shaft. For example, the arm may be engaged to the body by means of one or more guide pins. Conveniently, the arms include an opening to permit the shaft to pass through the arm, such that the arms may be positioned on either end of the body in a generally central position. Drawing the arms towards each other will thus urge the plungers inwardly towards each other, thereby releasing the shaft so as to slide and rotate freely within the clamp body, while urging the arms apart from each other has the opposite effect. It will be readily seen that the invention may work equally well in the reverse direction, whereby the grippers operate in the reverse direction and urging the arms apart would serve to grip the shaft to the clamp body. [0008] The grippers may be biased so as to urge the arms apart so as to fixedly engage the shaft unless the arms are urged together by a user to release the shaft. A solenoid motor or other linear actuator may join the respective arms, the motor being actuated by a controller so as to rapidly release or engage the grippers by urging the arms together or apart. [0009] The body is conveniently provided with bosses or other fasteners to permit the attachment of components. The bosses may permit the rotateable attachment of components to the clamp body. [0010] The present invention will now be further described by way of a detailed description of a preferred embodiment. It will be understood that this description merely illustrates an example of the invention and is not intended to limit the scope of the invention in any respect. Rather, a full scope of the invention is described in this specification as a whole, including the claims. It will be understood that unless otherwise specified, any element or component described herein may be replaced by an obvious mechanical equivalent. Further, directional or geometric references herein are not intended to be read in a strictly limiting sense, for example a reference to a "cylindrical shaft" may include a shaft having a non-circular cross-section. In similar fashion, directional references herein are generally provided merely for convenience of description. It will be understood that the invention may be readily used in any orientation. BRIEF DESCRIPTION OF THE DRAWINGS [0011] FIG. 1 is a side elevational view of the clamp, partly in section to illustrate the internal components. [0012] FIG. 2 is a side elevational view of the clamp body, showing internal elements in dotted lines. [0013] FIG. 3 is a front elevational view of the clamp. [0014] FIG. 4 is a perspective view of the clamp body. [0015] FIG. 5 is a perspective view of the clamp body engaged to a shaft and mounted to an optical component. [0016] FIG. 6 is a sectional view of an example of a prior art gripper for use in the present invention. DETAILED DESCRIPTION [0017] Referring to the Figures, the clamp body 10 comprises a suitable rigid material, such as a metal such as stainless steel or aluminum, or injection-molded plastic. The body includes a central bore 12 for receiving the shaft 14 in a manner which permits the shaft to slide and rotate freely within the bore when the clamp is in the released position. The bore is symmetrical about its elongate axis, with widened cylindrical recesses 16 at each of its opposed, outboard ends to receive a pair of opposed grippers 24, described below. The recesses 16 open to the opposed ends 18 of the body. The base of each recess 16 is inwardly stepped and comprises an annular shoulder 20 for abutting the outer sleeve 22 of a gripper 24, and a recessed pocket 26 to receive the inner sleeve 28 of gripper 24 to permit a degree of axial movement of the inner sleeve 28 relative to the outer sleeve 22 which is fixed in position. Protruding outwardly from opposing positions on either side of the body is a pair of bosses 30, for mounting a component to the body (not shown). The mountable component may comprise any suitable item or component which includes mating members for attachment to the bosses. It is contemplated that a useful application for the clamp is to fasten an optical instrument for use by optometrists to measure a patient's eyes. However, this is but one example of a suitable application. As will be seen in FIG. 5, the bosses may be provided with a lock 32 to fasten the component 33 to the bosses, and a pivot mount 34 to permit pivoting of the component. The component 33 is shown here as comprising an element of an optical system for measuring patient eyes. It will be readily seen that this is but one example of the many possible applications of the clamp. [0018] The shaft 14 extending through the central bore 12 is of any suitable material in cross-sectional configuration. It is contemplated that the shaft 14 is cylindrical, but it will be seen that the system may be adapted for use with shafts having other cross-sectional shapes. [0019] Inserted within each recess is a gripper 24, the preferred type being a somewhat modified version of the gripper sold under the trade-mark "Grip Fast.TM.". As seen in detail in FIG. 6, the gripper 24 comprises concentric inner and outer sleeves 28 and 22. The inner sleeve 28 includes a plurality of openings 29 to each receive a bearing 31 capable of extending partway through the openings 29. The outer sleeve 22 is associated with a wedge-shaped member 35 in contact with the bearings 31 such that when the sleeves are aligned the member 31 urges the bearings 31 partway through the openings 29, so as to tightly contact the shaft 14 to prevent axial movement of the shaft. A spring 37 or other biasing means urges the sleeves towards their aligned, gripping position. Continue reading about Electro-magnetic clamp for gripping a shaft... Full patent description for Electro-magnetic clamp for gripping a shaft Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Electro-magnetic clamp for gripping a shaft patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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