GB2135605A - Machine tool clamping device with rotating fluid pressure clamping cylinder - Google Patents

Abstract

The clamping device includes a rotating clamping cylinder (1) and therein a clamping piston (2) and a distributor (4) which comprises a distributor housing (5) carrying connections (6) for the operating medium and a distributor shaft (7) which is coaxially connected to the cylinder housing (1.1). The distributor housing (5) is so arranged that the distributor shaft (7) can rotate therein. The distributor shaft (7) has two shaft ducts (18, 19) which communicates with the connections (6) on the housing and which lead into the clamping cylinder (1) on opposite sides of the clamping piston (2). Associated with each shaft duct (18, 19) is a check valve (20, 21) for controlling the through-flow. The check valves (20, 21) are disposed in the peripheral wall (1.2) of the cylinder housing (1.1) with the directions of displacement of the valve members (32, 33) and the control pistons (26, 27) being parallel to the axis (16) of the cylinder. <IMAGE>

Description

SPECIFICATION Clamping device on machine tools with a rotating clamping cylinder The invention relates to a clamping device for a machine tool having a rotating clamping cylinder and a clamping piston disposed therein to rotate therewith, and a distributor including a distributor housing having ports for the passage of a medium for operating the piston and a distributor shaft connected in co-axial relationship with a cylinder housing for the clamping cylinder, the distributor housing being so arranged on the distributor shaft that the distributor shaft can rotate therein, wherein the distributor shaft has two shaft ducts which communicate with the housing ports and which lead into the clamping cylinder on opposite sides of the clamping piston, while associated with each shaft duct is a check valve for controlling the through-flow to and from the piston, the valve member of which check valve can be opened, against the flow of the operating medium, by a control piston which is subjected to the pressure of the operating medium in the respective other shaft duct.

In a clamping device of that kind, which is disclosed in German patent specification No.

1,91 1,558, the distributor shaft is mounted rotatably in the wall of the clamping cylinder and is fixedly connected to the clamping piston. The check valves are disposed with a direction of displacement, which is radial with respect to the axis of the cylinder, of the valve members and the control pistons, in the cylinder piston itself, with the shaft ducts also extending into the latter. At high speeds of rotation of the clamping cylinder, the above-mentioned radial directions of displacement can give rise to difficulties as the centrifugal forces acting on the valve members and the control pistons can detrimentally affect the valve function and because the radial movements of the valve members and control pistons can give rise to unbalance or alterations in imbalance.

In other clamping devices of the kind set forth in the opening part of this specification, as disclosed in German patent specification No.

1 ,006,236, French patent specification No.

1,417,689 or German Utility Model No.

19 85 828, the distributor shaft is fixedly connected to the cylinder housing of the clamping cylinder. The check valves may be disposed in a particular valve block which rotates with the distributor shaft, between the stationary distributor housing and the clamping cylinder, although that increases the structural length of the clamping cylinder and, because the valve members and the control pistons are also displaced in a radial direction in that arrangement, can give rise to the above-mentioned difficulties (German patent specification No. 1,006,236 and French patent specification No. 1,417,689), or the check valves may be disposed directly in the distributor shaft itself, with the valve members and the control pistons being displaceable in a direction parallel to the axis of the arrangement, although that requires a larger diameter on the part of the distributor shaft and the distributor housing mounted thereon and, at high speeds of rotation, involves a correspondingly large amount of heat being generated in the bearings mounting the distributor housing on the distributor shaft (German Utility Model No. 19 85 828). In addition, that known arrangement also results in the clamping device being of substantial axial lengths.

However, substantially axial lengths make it difficult to achieve dynamically precise balancing of the clamping device, for high speeds of rotation. For, under such conditions of use, it is necessary that the clamping device, being disposed in a cantilever position at the end of the spindle of the machine tool, is substantially free from imbalance not only over its axial length in total, but also in axially spaced cross-sectional planes which are normal to the axis of rotation, if the clamping device which rotates at high speed is not to be subject to flexural oscillations.

Accordingly, the invention is based on the problem of designing a clamping device of the kind set forth in the opening part of this specification, in such a way that it is of optimum short axial length, with an arrangement of the check valves, such that the clamping device is well balanced over its entire axial extent and the function of the check valve cannot be adversely affected by centrifugal forces.

According to the invention, that problem is solved in that the check valves are disposed in the peripheral wall of the cylinder housing, with the directions of displacement of the valve member and the control piston being parallel to the axis of the cylinder. Preferably, the check valves are disposed in diametrically opposing relationship with respect to the axis of the cylinder and at the same spacing from the axis of the cylinder. For each check valve, a valve chamber is desirably bored into the peripheral wall from the cylinder end, with the valve member and the control piston being positioned in the valve chamber in axial succession.

By virtue of the check valves being arranged with the direction of displacement of the valve members or control pistons thereof being parallel to the axis of the cylinder, the function of the valves cannot be adversely affected by the effect of centrifugal force as the centrifugal forces are normal to the above-mentioned directions of displacement. Therefore, movements of the valve members or control pistons also cannot give rise to any substantial imbalance phenomena or changes in imbalance. The peripheral wall of the cylinder housing has sufficient space in the axial direction for accommodating the check valves; the cylinder housing does not need to be extended in the axial direction for that purpose.

The virtually completely symmetrical arrangement of the check valves with respect to the cylinder axis provides a design configuration which can be equally well balanced over its entire axial length.

The same consideration also applies in regard to the distributor shaft which, being free of the check valves, can be of substantially rotationally symmetrical configuration, with shaft ducts only extending in diametrically opposing relationship in the distributor shaft.

An embodiment of the invention will be described hereinafter with reference to the accompanying drawings in which: Figure 1 shows a view in axial section through a clamping device, and Figure 2 shows a front view of the clamping device shown in Figure 1, viewed in the direction of the arrow II shown in Figure 1.

The clamping cylinder shown in the drawings, for clamping devices on machine tools, firstly comprises a cylinder housing 1 having a clamping piston 2 which is displaceable therein and which, in a screwthreaded bore 3, receives the clamping rod (not shown) in the machine spindle (also not shown). Normally, the cylinder housing 1 is secured to the end of the machine tool spindle and rotates therewith, including the clamping piston 2.

A distributor generally denoted by reference numeral 4 is connected to the clamping cylinder.

The distributor 4 comprises a distributor housing 5 which rotates with the clamping cylinder and which carries laterally positioned ports or connections 6 for the operating medium, Figure 1 showing the ports or connections 6 displaced through 1050 in order to make one of them visible. A distributor shaft 7 rotates in the distributor housing 5, being mounted in the distributor housing 5 by means of bearings 8, 9.

In that arrangement, one bearing 9 bears against a shoulder 10 of the distributor shaft 7 and is secured on the other side by a retaining ring 11.

The bearing 8 is arranged in a similar fashion so that the distributor housing 5 is accordingly axially immovable on the distributor shaft 7. The distributor shaft 7 is fixedly connected to the cylinder housing 1.1 of the clamping cylinder 1, more specifically, is formed in one piece therewith. Annular grooves 12 and 13 which extend around the inside of the distributor housing 5 serve to provide the feed and discharge of the operating medium and communicate directly with the ports 6 of the operating medium.

Leakage oil which passes between the distributor shaft and the distributor housing 5 is collected in ducts 14 and carried away through the ports or connections 1 5.

The distributor shaft 7 has two shaft ducts 18 and 19 which lead into the clamping cylinder 1 on opposite sides of the clamping piston 2. For the purposes of controlling the through-flow, check valves generally indicated by reference numerals 20 and 21 are associated respectively with the shaft ducts. The check valves are disposed in the peripheral wall 1.2 of the cylinder housing, with the directions of displacement of their valve members 32, 33 and control pistons 26, 27 being parallel to the axis 16 of the cylinder. They are disposed in diametrically opposing relationship with respect to the axis 1 6 of the cylinder, and at the same spacing from the axis 1 6 of the cylinder.

For each check valve 20 or 21, a valve chamber 22 or 23 is bored into the peripheral wall 1,2 from the end of the cylinder. The valve member 32 or 33 and the control piston 26 or 27 of the respective check valves are disposed in axial succession in the respective valve chamber. More particularly, connected to the ends of the shaft ducts 18 and 19 are the respective valve chambers 22 and 23 which each open at one side of the clamping piston 2, by means of respective openings 24 and 25. Each valve chamber 22 or 23 has a valve seat 28 or 29 for the valve member 32 or 33 of the respective check valve.

Each valve member 32 or 33 is displaceable by the respective control piston 26 or 27, for which purpose each control piston has a push rod for urging the valve members 32 and 33 of the respective check valves in the direction of opening so that, for opening the check valves 20 and 21 , the respective control piston is subjected to the pressure of the operating medium in the shaft duct 1 8 or 1 9, upstream of the respective other check valve, and causes opening of the respective check valve controlled thereby, against the flow of the pressure fluid. For that purpose, the valve chamber upstream of the control piston 26 is connected to the shaft duct 19 by way of conduit 19.1, and the valve chamber upstream of the control piston 27 is connected to the shaft duct 18 by way of conduit 18.1.Pressure oil or compressed air which enters through the annular groove 13 passes into shaft duct 19 and from there goes into the valve chamber 23 and by way of the valve member 33 of check valve 21 which opens under the pressure of the pressure fluid, the pressure fluid flows from the valve chamber 23 through the opening 25 into the cylinder chamber 39 disposed behind the clamping piston 2. At the same time, the pressure fluid acts on the control piston 26, from the side of the shaft duct 1 9, by way of the conduit 19.1. The control piston 26 moves and in so doing opens the valve member 32 of check valve 20 against the flow of the pressure fluid so that the pressure fluid can flow out of the cylinder chamber 40 which is in front of the clamping piston 2, through the opening 24, the valve chamber 22, the shaft duct 18 and the annular groove 12. In that case, the piston 2 moves into the limit position shown in Figure 1.

If the piston 2 is to be moved back, the pressure fluid circuit is reversed so that the pressure fluid is now supplied through the shaft duct 18, opens the valve member 32 of the check valve 20 and flows into the cylinder chamber 40 through the valve chamber 22 and the opening 24. At the same time, the pressure fluid actuates the control piston 27 from the side of the shaft duct 18 by way of the conduit 18.1 so that the valve member 23 opens the check valve 21 and the pressure fluid in the cylinder chamber 39 can flow away through the opening 25, the valve chamber 23 and the shaft duct 19.

Claims (4)

1. A clamping device for a machine tool having a rotating clamping cylinder and a clamping piston disposed therein to rotate therewith, and a distributor including a distributor housing having ports for the passage of a medium for operating the piston and a distributor shaft connected in coaxial relationship with a cylinder housing for the clamping cylinder, the distributor housing being so arranged on the distributor shaft that the distributor shaft can rotate therein, wherein the distributor shaft has two shaft ducts which communicate with the housing ports and which lead into the clamping cylinder on opposite sides of the clamping piston, while associated with each shaft duct is a check valve for controlling the through-flow to and from the piston the valve member of which check valve can be opened against the flow of the operating medium, by a control piston which is subjected to the pressure of the operating medium in the respective other shaft duct, the check valve being arranged in the peripheral wall of the cylinder housing with the directions of displacement of the valve members and the control pistons parallel to the axis of the cylinder.

2. A clamping device according to claim 1, in which the check valves are disposed in diametrically opposing relationship with respect to the axis of the cylinder and at the same spacing from the axis of the cylinder.

3. A clamping device according to claim 1 or claim 2, in which a valve chamber is bored into the peripheral wall of the cylinder for each check valve, parallel to the axis of the cylinder, and the respective valve member and control piston are located in the valve chamber in axial succession.

4. A clamping device for a machine tool, the device being substantially as hereinbefore described with reference to the accompanying drawing.