Field of the Invention

[0001] The present invention is directed clamping mechanisms and in particular to a rail brake or axis clamping apparatus for eliminating, or effectively eliminating, backlash in machining operations on a machine tool.

Background of the Invention

[0002] The production of complex geometry parts, such as gears and other toothed articles, on machine tools particularly multi-axis machine tools is well established. In general, such multi-axis machine tools may comprise one or more computer- controlled linear and/or non-linear (e.g. arcuate) axes of motion wherein for set-up and operation, machine components, for example, work piece tables, tool supports, slides, etc., are movable (usually linearly) in a desired direction of motion (e.g. X, Y or Z axis directions) via one or more ways or guide rails (e.g. a pair of spaced apart guide rails) on which the particular machine component is positioned. A bearing "truck" or "carriage" attached to the machine component and in engagement with the guide rails enables movement of the machine component along the guide rails.

[0003] Movement of each of the machine components is usually imparted by a separate drive motor preferably associated a feedback device such as a linear, or rotary, encoder as part of a computer numerical control (i.e. CNC) system which governs the operation of the drive motors in accordance with instructions input to a computer controller. Movement of the machine component may be provided by the drive motors through ball screws, by direct drive or by other means as is known to the skilled artisan.

[0004] In positioning a tool and work piece relative to one another before and/or during machining, precise positioning of the machine components along or about each respective machine axis is necessary so that the proper starting positions are achieved as are subsequent positions of machine components during the machining process. An incorrect axis position of any one component during a machining process can result in an unacceptable work piece being produced.

[0005] CNC control and drive systems comprising motors, encoders, ball screws, etc. are quite capable of correctly positioning machine components for machining operations. However, with machining and its related forces to which machine components are subjected, even the most accurate axis control and drive system lends itself to some amount of movement due to, for example, backlash (mechanical "play" or loose motion between contacting parts (e.g. gears)), the number of connections in a drive chain or other machine errors (e.g. skewing of rails, exceeding stiffness limitations of ball screws). Thus, while the drive system is likely capable of moving a component to a desired axis position, it may not be capable of holding a machine component in a particular axis position during machining without some amount of unwanted movement occurring. In processes where work piece tolerances are today expected to be in the range of a few millionths of an inch, even a thousandth of an inch (0.001 in.) (0.0254 mm) of movement can result in an out- of-tolerance work piece.

[0006] In an effort to address this undesirable movement, one or more rail brakes (i.e. axis clamps) are known to be utilized to lock a machine component in position along a guide rail. The rail brakes are attached to the machine component and surround a portion of the guide rail. When activated (e.g. hydraulically, pneumatically or electrically), a contact area of the brake is brought into contact with a surface of the guide rail to lock the position of the machine component on the guide rail. The intended result is that movement due to backlash or other undesirable factors from the drive system and/or from the carriage bearings is eliminated.

[0007] However, where tolerances are small, the present rail brakes may prove insufficient as unwanted motion due to moving parts within the rail brake mechanism itself, especially those parts whose direction of movement is in the same direction as the guide rails extend (i.e. the axial direction), may affect a machined workpiece to an extent such that the workpiece is still not within acceptable tolerances.

Summary of the Invention

[0008] The present invention is directed to a rail brake (i.e. axis clamp) wherein during braking, the movement of internal parts, particularly in the direction which the guide rails extend, is minimized such that backlash is eliminated, or effectively eliminated. The axis clamp includes a plate member attached to an axially movable component of the axis clamp as well as to a stationary component of the axis clamp.

Brief Description of the Drawings

[0009] Figure 1 illustrates a partially assembled axis clamp.

[0010] Figure 2 illustrates an axis clamp according to the present invention.

[0011] Figure 3 is a cross-sectional view of the axis clamp of Figure 2.

[0012] Figure 4 is an exploded view of the axis clamp of Figure 2. Detailed Description of the Preferred Embodiment

[0013] The invention will now be discussed with reference to preferred embodiments as illustrated by the accompanying drawings which are intended to be non-limiting and to represent the invention by way of example only. In the drawings, like elements will be identified with the same reference number. In the present application, the use of "axial direction" is understood to be the direction along which any referenced axis clamp travels or any guide rail extends.

[0014] Figure 1 shows a partially assembled axis clamp 2 of the present invention. The axis clamp 2 includes a body portion 4, a pair of jaws 6, pivot pins 8 and braking (clamping) pads 10. Body portion 4 comprises back surface 5, side surfaces 7 and end surfaces 9. Jaw 6 comprises pivot arm 11 and axial section 13. Located inside of body portion 4 (Figure 3) is a piston 12 associated with each jaw 6 such that outward movement of a piston 12 (such as by hydraulic or pneumatic pressure introduced via opening 14) effects pivoting of a jaw 6 about pivot pin 8 (pivot axis P) resulting in movement of the braking pad 10 toward and into contact with a guide rail (not shown). A bleeder plug is shown at 16.

[0015] It can be seen that the partially assembly of Figure 1 may function to clamp a machine component (to which is it attached) against movement in axial direction A along a guide rail. However, forces exerted on machine components during a machining process may be sufficient to produce small movements (e.g. backlash) of any attached clamp body 4 in the direction of the guide rail (axial direction A) due to, for example, gaps between adjacent clamp elements, such as gap 18 between body portion 4 and jaw 6, or movement of the body portion 4 along the pivot pins 8 which are oriented in the axial direction. In the manufacture of highly precise work pieces, even a very small shift of an axis clamp body 4 along a guide rail may be sufficient to move the associated machine component by an amount such that a tool or work piece will move out of its proper position resulting in an out-of-tolerance work piece. [0016] The inventors have discovered that the above-discussed movements may be eliminated, or effectively eliminated, by the inclusion of plate members 20 (Figures 2-4) preferably on each side surface of the axis clamp body portion 4. The plate members 20 are preferably made from spring steel (e.g. AIS1 1095 Steel) and preferably extend parallel to the axial direction of the guide rails. The plate members 20 are secured to the side surfaces 7 of the body portion 4 with fastening elements 22 located on both sides of the pins 8 (e.g. pivot axis P). Plate members 20 are secured by a plurality (preferably four) of fastening elements 22, such as screws and/or pins, to the body portion 4 of the axis clamp as well as to the jaws 6 of the axis clamp. Preferably, plate members 20 are secured to the body portion 4 near the intersection of body portion back surface 5 and side surfaces 7 and are secured to the jaws 6 at a location beyond the pivot pin 8 (with respect to piston 12) proximate the braking pads 10, most preferably to the jaw axial section 13 to which braking pads 10 are attached. The thickness of plate members 20 may vary. For example, a plate member having a length of 70 mm and a width of 30.5 mm preferably has a thickness of about 0.635 mm. Of course, for larger axis clamps and, hence, larger plate members, the thickness of the plate member may be increased. It follows, therefore, that smaller axis clamps may utilize thinner plate members.

[0017] With the plate members 20 secured to the axis clamp 2 in the manner described, movement of clamp elements in the axial direction is prevented, or effectively prevented, due to the jaws 6 being secured to the body portion 4. Even with gaps and/or mechanical connections in the axis clamp 2, the axis clamp is effectively a unitary body in the axial direction because plate members 20 do not permit any meaningful relative linear motion (e.g. as a result of gaps 18 or along pivot pins 8) to occur between the jaws 6 and the body portion 4 in the axial direction.

[0018] Although the plate members 20 are rigid with respect to movement in the axial direction, they do not prevent pivoting of the jaws 6 about pins 8 (and pivot axis P) and hence, movement of braking pads 10 into engagement with a guide rail. The properties of the spring steel allow the plates 20 to flex outward (perpendicular to the axial direction) when sufficient force is applied to push the pistons 12 outward thereby enabling the jaws 6 to pivot (clockwise in Figure 3, right side) about pins 8 and move the braking pads 10 inward to contact a guide rail. When the force is removed from the pistons 12, the spring steel plate members 20 return to their original state thereby pushing the pistons 12 inward and pivoting the jaws 6 (counter clockwise in Figure 3, right side) to disengage the braking pads 10 from a guide rail.

[0019] While the plate members 20 have been shown attached to the axis clamp assembly of Figure 1 , it will be appreciated that other axis clamp or linear brake assemblies may be utilized with plate members 20.

[0020] While the invention has been described with reference to preferred embodiments it is to be understood that the invention is not limited to the particulars thereof. The present invention is intended to include modifications which would be apparent to those skilled in the art to which the subject matter.