GB2068823A - Hydraulic control device for a mechanical press - Google Patents

Abstract

The invention relates to a control device for an excenter press with a spring loaded clutch-brake combination (KB) operated by a single-acting hydraulic motor (H) for respectively switching the drive of the slide of the press on and off and braking said slide. The device comprises in the inlet between the driving agent pump (P) and the motor cylinder (H) a hydraulically controlled seat valve (C1) and in the outlet between the cylinder (H) and the pressure agent tank (T) two hydraulically controlled seat valves (C2, C3) connected in parallel. These three seat valves are controlled by two pilot valves (V1, V2) at least one of which in its rest oposition sets the inlet valve (C1) in closed position and both pilot valves in their rest positions and via a common control pipe (s2) release the outlet valves (c2, c3) so that they allow the cylinder H free discharge to tank, and at least one pilot valve in actuated position releases the inlet valve (c1) so that it opens by the pump pressure and both pilot valves in actuated position connect the pressure side of the pump to the control pipe (s2) so that both outlet valves (c2, c3) close. <IMAGE>

Description

SPECIFICATION A control device for an excenter press Extensive requirements are put on safety against accidence in connection with work with excenter presses and with that also on the safety of the operating means present for switching the device of the slide of such a press on and off and for braking and holding the slide in rest at such a press. It is common practice for the operation of the mechanical clutch of the press between a power source and the slide to use a combination of clutch and brake, which can be actuated by a hydraulic motor.

Such a combination of clutch and brake for switching the drive of the slide on and quickly braking and holding the slide in a chosen idle position, respectively, is formed by a clutch which is provided in the power transmission path between the slide and the power source, a pressure spring loaded brake that effectively brakes the slide and the rest of the movable parts of the press interconnected therewith when the clutch is at rest, and a single-acting hydraulic motor which is set under pressure when the press is to carry out a working stroke, the motor, then, loosening the brake against the action of the pressure spring and setting the clutch for transmitting power from the power source to the slide.

The slide can be stopped by making the hydraulic motor pressureless so that it can return to its idle position under influence of the pressure spring, the clutch being released and the brake of the slide system actuated under influence of the spring.

Commonly applied safety requirements imply that valve movements in two mutually completely independent valve means must be provided concurrently in order for a press stroke to be initiated. Moreover, at least two mutually independent valve means connected in parallel must be provided in a return conduit for the pressure agent from the cylinder of the hydraulic motor to a pressure agent tank in order to make the hydraulic motor pressureless i.e. discharge the pressure agent from the cylinder of the hydraulic motor when the slide is tc be stopped so that the clutch does not remain in actuated position due to the fact that a single valve sticks in closed position .

A further safety at presses of this kind is, moreover, provided thereby that movements of valves of the hydraulic switching device are "actively" monitored meaning that is some pilot valve movement should fail to appear i.e.

some of the valves usually actuated against the action of a spring should stick in some position. further press strokes are prevented.

Hydraulic switching devices known hitherto for this purpose are built up around slide valves that physically have been doubled and actively monitored. However, such switching devices involve some disadvantages particularly with respect to the response rate of the press at connection and disconnecton. Particularly important is the requirement that the hydraulic operating device of the press should be quick to disconnect i.e. make the hydraulic motor actuating the clutch-brake of the press pressureless and thereby quickly let the spring operated brake have full effect in order to obtain as short stop times as possible and thereby obtain as short so called hand safety distances as possible.

According to the present invention deficiencies in this respect are eliminated in hitherto known safety designs of control devices for excenter presses in that the control device have characterizing features set forth in the attached claims.

The invention is described more in detail with reference to the attached drawing which shows a diagram of connections for an embodiment of a switching device according to the invention. In the diagram KB represents the combination of mechanical clutch and brake in an excenter press. The combination clutch-brake is actuated in one direction in which the clutch is disengaged and the brake engaged, by a spring F and can in order to carry out the press troke be actuated against the action of the spring F by a hydraulic motor H which when it is set under pressure, brings the combination clutch-brake to a position in which the brake is loosened and the clutch engaged. That well known arrangement is not shown in detail since it does not as such constitute part of the invention.The hydraulic system of the control device is supplied from a pump P in a normal arrangement with a check valve eV connected in parallel with a restriction r1 in the outlet from the pump, an overflow valve O for holding the working pressure constant and an ackumulator A for load equalization.

In an embodiment according to the invention the hydraulic system of the device is divided in two from each other hydraulically separated parts except for the supply of pressure agent; a control section having control circuits that comprise pilot valves V1 and V2 which constitute the means by which two mutually completely independent valve movements, are carried out before a press strike can be initiated, and a working section which comprise seat valves C1, C2 and C3 controlled from the control section in a connecting pipe between the pump and the tank to which the cylinder of the single-acting hydraulic motor H is connected.

The use of seat valves in a piping circuit which forms the inlet and outlet pipe for the cylinder of the hydraulic motor, leads to a considerably quicker execution of an intended operation than that which can be obtained by means of for this purpose hitherto normal sliding valves.

An arrangement using seat valves in a special working section to which the hydraulic motor is connected in which the necessary safety requirements are fulfilled, is made possible according to the invention in that the working section and the control section are mutually arranged as follows: As shown. the working section has in a pipe 11 from the pump one of the abovementioned controlled seat valves, inlet valve Cl the outlet of which being connected to a pipe 12 which constitutes inlet to as well as outlet from the hydraulic motor and is connected to inlets in each of the other seat valves, outlet valves C2 and C3, that are mutually connected in parallel with outlets via the pipe 13 to the tank.All valves C3 are hydraulically controllable to closed position whereas they are opened by an insignificant fluid pressure in the pipes, possible against the action of a matching spring force which, of course, particularly with resrject to the valves C2 and C3 cannot be so large that a fast discharge of the hydraulic cylinder upon disconnection is prevented.

The control section of the device comprises sliding valves V1 and !2 by means of which the two mutual lav cc,-l pgetel/ independent valve movements a-a provided which may be carried out in order to initiate a press stroke.

The shown valves are mutually fully parallel connected 4-way 4-wav - ion directional valves with inlets 1 the' Viâ 3 pressure pipe s1 via a restriction r2 are connected to the pressure side of the pump, and outlets 3 to tank via a pipe s3. With the valves in non-actuated condition their inlets 1 am connected to outlets 4 that jointly via a control pipe s4 are connected to the control means of the hydraulically controlled seat valve a in the pipe 11, 12 to the hydraulic motor 14 so that this valve Cl is kept closed to thereby prevent the pump in the piping circuit 11, C1, 12, C2 + C3, 13 from being short-circuited to sank. Already in this connection it should be mentioned that from a principle point of view only one of the sliding valves V1 and V2 needs to have an outlet which in rest supplies operating pressure to the seat valve C1 since pressure fluid from this one valve in rest can keep the valve Cl closed. This is indicated in the Figure by the interruption x in a flow path symbol in the valve V2 and in the pipe from the outlet 4 from this valve.The difference in the function of the device arising hereby, is not principle but a brief short-circuiting of the pump via valves C1 and C2 -t- C3 can arise if the pilot valve V1 is actuated somewhat before the pilot valve V2 upon initiation of a press stroke In rest with the ol!cleris 3 to tank the outlets 2 of the pilot valves /1 and V2 are interconnected and jointly interconnected with the hydraulic control means of the controlled seat valves Cl and C3 in the connecting pipe 12, 1 3, between the cylinder of the hydraulic motor and tank. As long as one of the valves V1 and V2 is non-actuated the valves C2 and C3, thus, are not kept closed and, consequently, the cylinder of the hydraulic motor cannot be pressurized.

When the two pilot valves Vl and V2 are actuated the inlets 1 of said valves are both connected to the outlets 2 connected to the ccontrol means of the outlet valves so that the control means of the outlet valves are actuated and keep the valves closed against pressure in the pipe 12.For pressurizing the control means of the valves C2 and C3 it is necessary that both pilot valves V1 and V2 are actuated as in known center presses controlled only by means of sliding valves since upon actuation of only one of the valves the control circuit is short-circuited via the other valve without any build-up of the neces- sary operating pressure. a At ehe same time as the connection for pressure agent is established from the pump to the hydraulic actuating means of the outlet valves C2 and C3 a connection is established (at least in one of the pilot valves Vl, V2) between the outlets 4 of the valves (the valve) connected to the control means of the inlet valve Cl to tank via the outlets 3 of the valves (the valve), whereby the inlet valve C1 can open and pressure agent be supplied to the hydraulic motor H for initiating a press stroke.

As soon as one of the pilot valves V1 and V2 returns to its idle position the hydraulic actuating means or the outlet valves are connecked to tank and, consequently, the valves can open and the hydraulic motor H under influence of the spring F can return to idle position in which the clutch is disengaged and the brake engaged.

The safety requirements on a system of the present kind are fulfilled what concerns the hydraulic circuits of the system by the doubling of the outlet valves C2, C3 and the doubling of pilot valves analogous to known control devices. The required "active monitor- ing" of valve moments is indicated by contact symbols el at the outlet valves C2 and C3 and with the symbol e2 for a pressure controlled contact device connected to the pressure side of the inlet valve Cl.

Claims (3)

1. A control device for an excenter press with a hydraulically operated combination lKE) of clutch and brake for respectively switching the drive of the slide of the press on and off and braking the slide after switch-off and in rest, in which the clutch-brake combination is formed by a clutch which is provided in the power transmission path between the slide and the power source of the press, and a oressure sparing loaded brake which brakes the slide when the clutch is in its off-position, and comprising a single-acting hydraulic motor (H) supplied with a pressure agent from a pump (P) when the press is to carry out a working stroke, it, then, loosens the brake against the action of the pressure spring (F) and sets the clutch for transmitting power from the power source to the slide, and which is made pressureless when the slide is to be stopped, the motor, then, being brought pack to its idle position under influence of the spring, the clutch being released and the slide being braked, characterized in that the control device comprises in a pipe (p, 11, 12) between the pump (P) and the cylinder of the motor (H) a hydraulically controlled seat valve below caled inlet valve (c1), and in a connecting type (12, 13) between the cylinder and a pressure agent tank (T) at least two hydraulically controlled seat valves, below called outlet valves (C2, C3), that are mutually connected in parallel as regards the control as well as the pressure agent flow, and for actuating said three seat valves (C1, C2, C3) hydraulic control circuits comprising two pilot valves (V1, V2) having an idle position and an actuated position, at least one (V1) of said pilot valves in its idle position setting the inlet valve (c1) in closed position by connecting the hydraulic actuating means of the inlet valve to the pressure agent source (P) and both pilot valves (V1 and V2) in their idle position releasing the outlet valves by connecting the hydraulic actuating means of the outlet valves to tank via a common control pipe (s2) so that the outlet valves enable free discharge of the pressure agent from the cylinder of the hydraulic motor to tank, and that said at least one pilot valve (V1) in its actuated position releases the inlet valve by connecting the hydraulic actuating means of the inlet valve (C1) to tank to open a connection between the pressure side of the pump and the cylinder of the hydraulic motor (H) and both pilot valves (V1 and V2) in actuated position connecting the pressure side of the pump to said control pipe (s2) common to the two pilot valves to close the outlet valves (C2 and C3) when both pilot valves are actuated at the same time.

2. A control device as claimed in claim 1, characterized in that the both pilot valves (V1 and V2) in their idle position connect the hydraulic actuating means of the inlet valve to the pressure side of the pump.

3. A control device as claimed in claim 1 and substantially as hereinbefore described with reference to and as shown in the accompanying drawing.