Work-clamping unit for use in machine tools

DETAILED DESCRIPTION OF THE INVENTION Referring to FIGS.
1 and 2, a drilling machine (M) includes a horizontal table 1 on which a clamp unit (C) is mounted.
The clamp unit (C) has a flat top surface 2 on which a work (W) is held by means of clamping members.
The clamping force is imparted to the clamping members 3 in the form of hydraulic pressure, which is fed from a hydraulic supply source (S) through a pipe 4.
Referring to FIGS.
3 to 6, the clamp unit (C) will be explained in greater detail: The clamp unit (C) includes a base plate 5 as a matrix, made of a thick steel in which 15 hydraulic cylinders (H) are totally embedded at equal spaces so as to form 3 lines and 5 rows as best shown in FIG.
3.
The hydraulic cylinders (H) are single-acting types, each consisting of a stationary section 6 and a movable section 7.
The stationary section 6 is the cylinder itself, and the movable section 7 is a piston.
The cylinder 6 is fitted in a hole 5a produced in the under-surface of the base plate 5.
The piston 7 is inserted in the cylinder 6 and vertically moves within the limit that its rod 7a never rises up the top surface 2 of the base plate 5.
When an oil is introduced into an oil chamber 8, the piston 7 is caused to descend against a spring 9, and when the oil is withdrawn, the piston 7 restores under the action of the spring 9.
The cylinder 6 has a shoulder 6a, and the piston 7 has a shoulder 7b.
When the piston 7 ascends, these shoulders come into abutment, and the piston 7 is prevented from its further upward movement.
The hydraulic cylinders (H) in the same line are communicated by an oil path 10 passing through the base plate 5 such that the oil chambers 8 in each cylinder are communicated one after another.
The oil path 10 is supplied with oil at a port 11 at which the pipe 4 is connected to the base plate 5.
The piston rod 7a includes a hole 12 so threaded as to receive a threaded portion of a clamping bolt 3, thereby effecting their associated movement.
The clamping bolt 3 includes a head (P), which is intended to hold a workpiece (W) against the top surface 2 of the base plate 5