Work Support

Abstract: A support rod (3) vertically movably inserted into a housing (2) is urged upward by an advancing spring (4). An annular piston (6) is inserted between a barrel portion (2c) of the housing (2) and an outer peripheral surface of the support rod (3). A collet (10) externally fitted onto a holding and fixing portion (C) of the support rod (3) is received by a lower end wall (2b) of the housing (2). A tapered transmission member (17) externally fitted onto the collet (10) is urged downward by a holding spring (22). The urging force clamps the support rod (3) at a predetermined height through the collet (10).

Description: BACKGROUND OF THE INVENTION Technical Field The present invention relates to an apparatus for supporting a work when machining the work by a milling machine, a grinder or the like machine tools. Explanation of Prior Art Generally, a work support of this type is adapted to hold a support rod at a predetermined height through a collet with a pressurized fluid supplied to a clamping actuation chamber (for example, see Japanese Utility Model Publication No. 6-7868 proposed previously by an Assignee of the present Applicant). Though the above-mentioned conventional technique is excellent in that it can strongly hold the support rod with fluid pressure, it has a problem that the foregoing holding force disappears when the actuation chamber loses its pressure due to the leakage of the pressurized fluid or the like. SUMMARY OF THE INVENTION The present invention has an object to solve the aforesaid problem of the conventional technique. The invention is defined in claim 1. A document disclosing the features in the pre-characterising part of claim 1 is US-A-3 643 765. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a vertical sectional view of a first embodiment of the present invention. Fig. 2 is a vertical sectional view of a second embodiment of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a first embodiment of the present invention is explained with reference to Fig. 1. A housing 2 of a work support 1 comprises an upper end wall (first end wall) 2a, a lower end wall (second end wall) 2b and a barrel portion 2c. And it is fixed to a table (T) by a plurality of bolts (not shown). A support rod 3 is vertically movably inserted into the housing 2. The support rod 3 projects upwards by an advancing spring (advancing means) 4 and its upper end comes to contact with a work (W). A bolt 5 regulates the projecting length of the support rod 3. Further, an attachment (not shown) may be brought into screw-thread engagement with a female screw 3a provided in an upper end of the support rod 3 so as to be vertically adjustable and made to contact with the work (W) at its upper portion. An annular clamp chamber (A) is formed between the barrel portion 2c of the housing 2 and an outer peripheral surface of the support rod 3. A spring chamber 7 is formed on an upper side of a piston 6 inserted into the clamp chamber (A) and a hydraulic actuation chamber (fluid-pressure actuation chamber) 8 is formed on a lower side of the piston 6. A holding and fixing portion (C) is provided at a lower side portion of the outer peripheral surface of the support rod 3 and a cylindrical collet 10 is externally fitted onto the holding and fixing portion (C). The collet 10 is adapted to diametrically contract owing to elastic deformation by a single slit 11 extending vertically. The collet 10 is also formed on its outer periphery with an upwardly tapered pressure receiving surface 12. The collet 10 is urged downward by a return spring 13, which is a return means, to be received by the lower end wall 2b. Numeral 14 designates a spring retainer. A tapered transmission member 17 to be externally fitted onto the collet 10 is composed of an outer cylinder 18 placed on an upper surface of the piston 6 and an inner cylinder 19 serving as a low friction liner. The pressure receiving surface 12 is engaged with a pushing surface 20 formed on an inner surface of the inner cylinder 19 and upwardly tapered. Attached between a lower portion of the outer cylinder 18 and the upper end wall 2a is a holding spring 22, which is composed of a compressed coil spring rectangular in section. The work support 1 operates as follows. When supporting the work (W) from below, pressurized oil is first supplied to the hydraulic actuation chamber 8 through a supply and discharge port 24. Then, as shown, the piston 6 moves the transmission member 17 upward against the holding spring 22 to release the diametrical contraction of the collet 10 and the advancing spring 4 makes the support rod 3 lightly contact with the under surface of the work (W). Next, when the pressurized oil within the actuation chamber 8 is discharged, the transmission member 17 is moved downward through the urging force of the holding spring 22 and the pushing surface 20 of the inner cylinder 19 comes into tapering engagement with the pressure receiving surface 12 of the collet 10. Thus the collet 10 diametrically contracts, so that its inner surface radially pushes the holding and fixing portion (C) of the support rod 3 and holds the support rod 3 at an illustrated height. Incidentally, if a tapering angle of the pressure receiving surface 12 of the collet 10 is set at about 4°, there is produced a holding and fixing force which is about two to three times the urging force of the holding spring 22. As a result, the support rod 3 can be strongly held. Subsequently, an upper surface of the work (W) is machined. After the machining has been completed, it is enough if pressurized oil is supplied again to the actuation chamber 8 so as to cancel the clamping condition of the support rod 3. The work support 1 of the foregoing construction has the following advantage when compared with the above-mentioned conventional work support of hydraulic clamp type. According to the conventional technique, any hydraulic force does not act in unclamping condition while a strong hydraulic force acts in clamping condition. Therefore, a big difference occurs between these two conditions in the amount of the elastic deformation caused axially of the housing. However, the present invention does not cause such a big difference for the following reasons. In the unclamping condition shown in Fig. 1, the holding spring 22 has an urging force (e.g. about 500 kgf) greater than in the clamping condition because it is compressed by the upward movement of the piston 6. The urging force of the spring 22 is received by the lower end wall 2b through a lower portion of the transmission member 17, the piston 6 and an oil column of the actuation chamber 8, and it is also received by the upper end wall 2a, thereby pulling the housing 2 axially to elastically deform it. When the pressurized oil within the actuation chamber 8 is discharged so as to switch over from the unclamping condition to the clamping condition, the holding spring 22 is extended to bring the transmission member 17 into tapering engagement with the collet 10. Thus the urging force of the spring 22 is received by the lower end wall 2b through the transmission member 17 and the collet 10, and it is also received by the upper end wall 2a, thereby pulling the housing 2 axially to elastically deform it as in the case of the unclamping condition. The urging force of the spring 22 in the clamping condition is e.g. about 450 kgf, which is substantially the same as that in the unclamping condition because it only decreases in correspondence with the length extended for the tapering engagement. Accordingly, on switching over from the unclamping condition to the clamping condition, there is not caused a big variation in the pulling force acting on the housing 2, which in turn prevents a big difference from occurring in the amount of the elastic deformation caused axially of the housing 2. As a result, the present invention can inhibit the height of the holding and fixing portion (C) of the support rod 3 from varying with respect to the housing 2 to thereby increase the accuracy of the machining dimension of the work (W). The above first embodiment further presents the following advantage. It is possible for the collet 10 to be attached at a lower portion within the housing 2, so that the height of the holding and fixing portion (C) of the support 3 can be lowered. Therefore, the collet 10 deforms by compression through the urging force of the holding spring 22 in a reduced amount. As a result, the height of a leading end of the support rod 3 held and fixed to the collet 10 varies only by a small amount to further enhance the accuracy of the machining dimension of the work (W). Notably, in the above embodiment, the piston 6 and the transmission member 17 may be formed in an integral structure instead of being formed separately from each other as shown. Further, the urging force of the holding spring 22 may be made to act on the transmission member 17 through the piston 6 instead of directly. Next, a second embodiment of the present invention is explained with reference to Fig. 2. In this second embodiment, the members of the same constructions as those of the first embodiment are in principle designated by the same characters. In this embodiment, the piston 6 is composed of an O-ring which is a sealing member. Further, a retaining ring 30 regulates the projecting length of the support rod 3. Besides, the urging force of the advancing spring 4 is adjusted by a bolt 31 threadably engaged with the female screw 3a of the support rod 3. The upper end wall 2a of the housing 2 is secured to the barrel portion 2c by a plurality of bolts (not shown). The foregoing respective embodiments can be modified as follows. The collet 10 may be provided with plural slits instead of such a single slit 11 as exemplified. In addition, the collet 10 may be formed from plural segments instead of being formed as an exemplified integral unit. In this case, the diametrical contraction of the segments may be released either by their own elastic restoring force or by a separately provided spring for diametrical expansion. The advancing means 4 may employ either other kinds of elastic members such as rubber or compressed air instead of a spring. The holding spring 22 may have a circular section instead of a rectangular section. A pressurised fluid to be supplied to the actuation chamber 8 may be air or like gases instead of a liquid such as pressurised oil. The work support 1 may be disposed so that the axis of the support rod 3 is directed horizontally or slantingly instead of vertically.

Claims: A work support comprising. a housing (2); a support rod (3) having a holding and fixing portion (C) and mounted in the housing (2) for movement along the axis of the rod; an advancing means (4) for advancing the support rod (3) outwardly of the housing (2); a collet (10) externally fitted onto the holding and fixing portion (C) and received by the housing (2); a tapered transmission member (17) externally fitted on the collet (10); a holding spring (22) for moving the transmission member (17) in a first direction along the axis so as to diametrically contract the collet (10), an exterior pressure-receiving surface (12) of the collet (10) inwardly tapering in a second direction away from the piston (6), an adjacent inner surface of the transmission member (17) being correspondingly tapered; and an annular fluid-pressure piston (6) for moving the transmission member (17) against the spring (22) in said second direction along the axis so as to release the diametrical contraction of the collet (10): characterised in that . (a) the annular fluid-pressure piston (6) has an outer peripheral surface and an inner peripheral surface both hermetically supported by respective parts (2b, 2c) of the housing (2); (b) the holding spring (22) is mounted in an annular space between the tapered transmission member (17) and a barrel portion (2c) of the housing (2); and (c) a low-friction liner means (19) is disposed between the exterior pressure receiving surface of the collet (10) and the said inner surface of the transmission member (17). A work support according to claim I wherein the low-friction liner means (19) is a tapered cylindrical liner. A work support according to claim 1 or 2, wherein the collet (10) is adapted to be movable along the axis within a predeternlined range, a return means (13) being mounted so as to urge the collet (10) in said first direction. A work support according to any foregoing claim, wherein the annular piston (6) is constructed separately from the transmission member (17). A work support according to any of claims 1 to 4, wherein the piston (6) is composed of a sealing member received by the transmission member (17).

Inventors: YONEZAWA KEITARO, YONEZAWA, KEITARO
Applicants: KOSMEK KK, KABUSHIKI KAISHA KOSMEK
Application year: 1997
Main classification: B23Q3
IPC codes: B23Q3, B23B31