Patent EP-2314415-A1 (EP)
Inventor: TATSUDA YOSHINORI
IPC: B23Q16/10
Filed: 2009-10-26
Abstract: The present invention relates to a main shaft driving device (1) for a machine tool comprising a frame (2), a main shaft (4a), a driving device (6, 9), and a clamping device (10), wherein the main shaft is rotatably supported by the frame (2) and rotationally driven by the driving device (6, 9), the main shaft (4a) has a member that is rotationally driven (5) secured to an end portion thereof, the clamping device (10) includes a clamp piston (44), a pressure chamber (36a, 36b, 49a, 49b), and an operating fluid supplying mechanism (42), the clamp piston (44) being provided so as to be displaceable in an axial direction of the main shaft (4a) with respect to the frame (2), the clamp piston (44) including a pressure-receiving surface (35a, 35b) and a braking portion (31a, 31b, 44c), the pressure-receiving surface (35a, 35b) receiving pressure of an operating fluid, the braking portion (31a, 31b, 44c) causing a press-contact force to act upon the main shaft (4a), the pressure chamber (36a, 36b, 49a, 49b) is formed by the pressure-receiving surface (35a, 35b) and the frame (2), the operating fluid supplying mechanism (42) is provided for supplying the operating fluid from an operating fluid supply source to the pressure chamber (36a, 36b, 49a, 49b), wherein the press-contact force is caused to act upon the main shaft (4a) by displacing the clamp piston (44) towards the main shaft (4a) by the pressure of the operating fluid that is supplied to the pressure chamber (36a, 36b, 49a, 49b), characterized in that: 
the clamping device (10) includes a spring member (61) that urges the clamp piston (44) in a first direction, which is the same as a direction in which the braking portion (31a, 31b, 44c) causes the press-contact force to act upon the main shaft (4a), the spring member (61) causing a spring force to act upon the pressure-receiving surface (35a, 35b), the spring force causing the press-contact force that causes the main shaft (4a) to be set in a partially clamped state to act upon the main shaft (4a) by the braking portion (31a, 31b, 44c), 
the clamp piston (44) has a first pressure-receiving surface (35a) and a second pressure-receiving surface (35b), the first pressure-receiving surface (35a) extending in a second direction that is orthogonal to the first direction and receiving pressure of an operating fluid in the first direction, the first pressure-receiving surface (35a) receiving the spring force of the spring member (61), the second pressure-receiving surface (35b) extending in the second direction and receiving pressure of an operating fluid in a direction opposite to the first direction, and 
the operating fluid supplying mechanism (42) includes a switching portion (48) that selectively supplies the corresponding operating fluid from a common operating fluid supply source to either the first or the second pressure chamber (36a, 36b, 49a, 49b), the first pressure chamber (36a, 49a) being formed by the first pressure-receiving surface (35a) and the frame (2), the second pressure chamber (36b, 49b) being formed by the second pressure-receiving surface (35b) and the frame (2).