TECHNICAL FIELD OF THE INVENTION

This invention relates to a manual control device for power assisted presses having fixed and movable tool heads .

BACKGROUND

Power operated presses are widely used in many manufacturing industries. The power source employed may be pneumatic, hydraulic or other means. In each case the power may be transmitted directly or through a mechanism providing a mechanical advantage, typical examples being a toggle linkage or rack and pinion drive.

The traditional method of using a press requires the operator to manually position the workpiece (or pieces) move their hands clear of the press tooling, and operate a switching device. The press then extends and retracts its ram together with any tooling which is connected thereto. Because the movement of the ram is automatic, much legislation exists concerning the guarding of power presses, with the aim of preventing the operator from approaching the workpiece during press operation. Because the movement of the ram is automatic, the operator is also denied any feel of the forces being used in the process. Divorcing the operator from the process in this way makes tasks which

require a degree of precision or force-dependent feedback -jery difficult to carry out.

EP 0 332 420 discloses an hydraulic press which is manually controllable by rotation of a lever secured to a horizontal shaft, which in turn rotates a vertically extending shaft of a hydraulic control mechanism of the press. Where there is no resistance to movement of the respective tool head, rotation of the horizontal shaft results, by virtue of a screw mechanism, in rectilinear movement of the movable tool head without any hydraulic assistance. However, as soon as resistance to movement of the movable tool head is experienced, the movable head is provided with hydraulic assistance. The hydraulic assistance is brought about by operation of an hydraulic control valve upon application of a sufficient torque to a torsion bar. This press requires a considerable amount of precision engineering, and the valve arrangement must be incorporated into the press during manufacture thereof.

An aim of the present invention may be viewed as being to provide an inexpensive and reliable means of manually operating a power assisted press without requiring extensive modification or re-designing of the press itself.

SUMMARY OF THE INVENTION

The present invention proposes a manual control device for a power assisted press having fixed and movable tool heads, the control device including a rotatable drive shaft for generating movement of the movable tool head towards and away from the fixed tool head, a

rotatable input shaft mounted for rotation about a generally horizontal axis, drive transmission means coupling the said shafts, a manual operating lever coupled to said input shaft and angularly movable in a substantially vertical plane to cause rotation of said drive shaft, CHARACTERISED IN THAT the drive transmission means comprises a pair of relatively rotatable members coupled to the respective shafts, one of said rotatable members being provided with first abutment means carrying sensor means for initiating power assistance and the other of said rotatable members carrying second abutment means disposed to operate said sensor means upon relative rotation of the two members, and resiliently compressible means disposed between the said abutment means and arranged to prevent operation of said sensor means until a torque differential exists between the two shafts which is sufficient to cause compression thereof.

The rotatable members are preferably provided with respective sensor means and compressible means, disposed on opposite sides of said axis of rotation. The reaction forces between the two rotatable members are therefore balanced about the axis of rotation.

The rotatable members may comprise a pair of discs arranged co-axially in face-to-face relationship.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description and the accompanying drawings referred to therein are included by way of non-limiting example in order to illustrate how the invention may be

put into practice. In the drawings:

Figure 1 is a partially sectioned view of a controller assembly of the invention,

Figure 2 is a partially sectioned view of a drive plate of the controller assembly, and

Figure 3 is an isometric view of the drive pi ate.

DETAILED DESCRIPTION OF THE DRAWINGS

The controller assembly is mounted on the side of a conventional pneumatically operated power press having a drive shaft 1. Rotation of the drive shaft is arranged to mechanically move a tool head towards and away from a fixed tool head, in any convenient manner.

An input handle 5 is rigidly attached to a collar 4. Input force from the press operator is transferred through the collar 4 to an input shaft 3 via a mechanical key 6 or similar means. The collar 4 is retained on the shaft by a nut and washer 20 or other mechanical means. The input shaft 3 is supported by, and passes through, an outer mounting plate 8 via a bush 7. The torsional force introduced by the operator is then transmitted from shaft 3 to an input drive backing plate 9 via a mechanical key 10 or similar means. An input drive plate 11 is rigidly attached to the backing plate 9 by screws, welding or similar means. As shown in Fig.s 2 and 3, the input drive place 11 carries a mounting plate 21 and a pressure

plate 22, which lie on spaced parallel planes on opposite sides of the axis of shaft 3. The plates 21, 22 are also staggered in the direction of the planes, as shown. The mounting plate 21 carries an on/off switching device 12, which may be powered by electrical, pneumatic or other means. A resiliently flexible collar element 13 is located about the switching device 12 so that the device 12 cannot be operated until the flexible element 13 has been compressed. A second drive plate 14 (the output drive plate) is similarly provided with a switching device 12 and flexible element 13, but the output drive plate is substantially a mirror image of the input drive plate 11. When assembled in the controller the input drive plate 11 and the output drive plate 14 are arranged concentrically about the input shaft 3, arranged such that each flexible element 13 abuts a pressure plate 22 of the opposed drive plate.

Referring back to Fig. 1, the output drive plate 14 is not rigidly fixed to the input drive shaft 3, but is allowed to rotate concentrically about the shaft via a bush 15. This bush supports the end of shaft 3 in an inner mounting plate 23 and also supports an output drive gear 16 which is rigidly attached to the output drive plate 14 by screws, welding or similar means. The output drive gear 16 is in constant mesh with an input drive gear 2 which is connected to the press drive shaft 1 via a mechanical key or similar means. It can thus be seen that the press drive shaft 1 will be caused to rotate in direct proportion to the output drive plate 14.

In use, as the operator rotates the input shaft 3 via

the input handle 5, the inpu-. drive plate 11 attempts to rotate the output drive slate 14. The amount of resistance to this rotation will be in direct proportion to the torque required to rotate the press drive shaft 1, which is directly determined by the resistance to movement of the press ram. When this resistance is small, the torqje required to rotate the press drive shaft 1 will be transmitted directly through the controller, i.e. the operator will have full manual control. As the torque required to rotate the press drive shaft 1 inc-eases, so the amount of torque being transmitted through the controller increases. Since the input drive plate 11 and the output drive plate 14 are separated by the flexible elements 13, as the torque increases, the compression of the flexible elements increases. When the amount of compression allows the switching devices 12 to operate, a pneumatic ram in the press ^_' s thereby activated. As the ram moves, the press dr- ^' ve shaft 1 is caused to rotate, and this in turn causes the output drive plate 14 to rotate in the opposite direction. The net result is that a relative rotational movement takes place between the drive plate 11 and 14, and releases the switching devices 12. Thus, the press ram is powered only for as long as the operator applies sufficient force to the lever 5 to keep the flexible elements 13 compressed.