GB2025561A - A compressed air actuated control device comprising two- handed actuation - Google Patents

Abstract

This invention relates to a compressed air actuated control device 10 with two-handed actuation in which control signals from two pushbuttons 13 and 14 have to be released at least substantially simultaneously for the control of a working piston 11, for example of a press. The control device simply comprises two 5/2-multiway valves 17 and 18 which are so connected to one another and to the pushbuttons 13 and 14, with the interposition of a timing element 22, that a safety locking is achieved thereby. <IMAGE>

Description

SPECIFICATION A compressed air actuated control device comprising two-handed actuation State of the art The invention originates from a compressed air actuated control device comprising twohanded actuation according to the type set forth in the main claim. Such a control device is already known in which the functions of safety locking as well as simultaneous switching and self-monitoring are met to a considerable extent but which require, however, three similar 5/2-multiway valves in a special circuit arrangement for the purpose. A disadvantage with this control device is that the expenditure is relatively high due to the use of three multiway valves and their associated circuitry.

Also the safety of the control device is influenced disadvantageously due to the danger that components can fail when using three multiway valves.

Advantages of the invention As opposed to this, the control device in accordance with the invention comprising the characterising features of the main claim has the advantage that it involves substantially less expenditure without reducing the operational capabilities of the safety locking. Thus, instead of the previous three 5/2-multiway valves it only requires two 5/2-multiway valves whereby the cost is reduced correspondingly. Moreover, the safety locking prevents a signal from occurring at the load port, not only when the pushbuttons are actuated separately or with too great an interval between them, but also when, on simultaneous actuation of the pushbuttons, a signal has existed previously at the load port and when the actuation is interrupted only temporarily by one pushbutton.Furthermore, the safety of the control device is increased by using only two multiway valves; the danger of a valve slide jamming or a spring breaking in the third multiway valve is excluded so that a failure can only occur in respect of components of the two multiway valves.

Further advantageous developments of the subject-matter of the invention will become apparent from the other sub-claims, the description and the drawing.

Drawing An embodiment of the invention is illustrated in the drawing by way of example and is described in more detail in the following specification.

Figure 1 shows the circuit diagram of a control device comprising two-handed actuation, Figure 2 is a diagram showing the input and output signals, and Figure 3 is a second embodiment of the control device.

Description of the invention The control device 10 illustrated in Fig. 1 serves for the control of a working piston 11 operated by compressed air of a machine tool, such as a press for example, not illustrated in detail. The purpose of the control device 10 is to prevent damage to the hands during dangerous advancing movements of the machine tool by forcing the operator to maintain the hands outside the danger zone. The control device 10 consists of a control unit 1 2 and two pushbuttons 13, 14 to be operated separately which are formed as 3/2-multiway valves.

The compressed air for operating the working piston 11 is obtained from an optional compressed air source 1 5 through a compressed air supply line 1 6. The first pushbutton 1 3 and the second pushbutton 14 are illustrated in Fig. 1 in their neutral position in which they generate no control signal. The outputs from the two pushbuttons 13, 1 4 are connected to the control unit 1 2.

The control unit 1 2 is formed by two compressed air actuated 5/2-multiway valves 17, 1 8 with spring return. Each of the 5/2multiway valves has an actuating port Z, three inputs R, P, S and two outputs A, B. In the neutral position 1 9 of each of the 5/2-multiway valves 17, 1 8 illustrated in Fig. 1, the first output A is connected to the second input P and the second output B is connected to the first input R. The third input S is blocked. In the second switching position 21, the first output A is connected to the third input S, the second output B is connected to the second input P, wherein the first input R is blocked.

(In the following, the reference letters to the ports of the 5/2-multiway valves (17, 18) are each provided with an index corresponding to the reference numeral of the multiway valve).

The actuating port Z,7 of the first 5/2-multiway valve 1 7 is connected to the output from the first pushbutton 1 3. The first input R,7 is ventilated, the second input P,7 is connected to the output from the second pushbutton 14 and the third input S,7 is connected to the compressed air supply line 1 6. The first output A,7 from the first multiway valve 1 7 is connected through a timing element 22 to the first input R,8 to the second multiway valve 1 8 whilst the second output B,7 to the first multiway valve 1 7 is connected to the actuating port Z,8 of the second multiway valve 1 8. Of the second multiway valve 18, the second input P,8 is ventilated and the third input S,8 is once more in communication with the compressed air supply line 1 6. The first output A,8 from the second multiway valve 1 8 is in communication with the load port 23 and furthermore with the working piston 11. From the second output B,8 from the same multiway valve 18, a line leads to a second actuating port Y,8 of the second multiway valve 18, which is arranged at the return spring end and thus opposite the first actuating port Z,8.

The timing element 22 referred to is formed by a non-adjustable throttle non-return valve 24 and a chamber 25 in series therewith.

All the multiway valves 17, 1 8 and the timing element 22 may with advantage be screwed onto a common channel guide plate which is not described in detail and which provides a control device of compact construction.

The operation of the control device 10 is as follows, wherein reference is also made to Fig.

2: If, as is apparent from case 1 in Fig. 2, only the pushbutton 1 3 is actuated on its own, then the first multiway valve 1 7 switches into its second switching position 21. In so doing, compressed air from the supply line 1 6 arrives at the actuating port Y,8 through the first multiway valve 17, the timing element 22 and the second multiway valve 1 8 remaining in its neutral position. The load port 23 remains ventilated through the output A,8 and the second input P,8 so that no control signal can form at that location.

On the other hand, if only the second pushbutton 14 is actuated on its own, as is shown in case 2 in Fig. 2, then the first multiway valve 1 7 remains in the illustrated neutral position 1 9 and compressed air can arrive from the supply line through the first multiway valve 17, the timing element 22 and the second multiway valve 1 8 at the actuating port Y,8. The load port 23 is ventilated through the second multiway valve 18; a control signal cannot exist at that location.

If both pushbuttons 13, 14 are actuated, as shown in detail in case 3 in Fig. 2, then pressure exists at the load port 23 and as a consequence in the working piston 11, only when control signals have been generated at least substantially simultaneously by the pushbuttons 13, 14. On actuating the pushbutton 13, the first 5/2-multiway valve 1 7 is of course moved into its second switching position 21. In this switching position, compressed air arrives at the timing element 22 from the supply line 1 6. A short time later, by operating the second pushbutton 14, the operator must generate a control signal which finally brings the second 5/2-multiway valve 18 into its second switching position 21 in which the first input R,8 of the second 5/2multiway valve 1 8 connected to the timing element 22 is closed.Moreover, the control signal generated by the second pushbutton 14 must happen so quickly that still no pressure signal arriving through the delay element 22 exists at the first input R,8 to the second 5/2-multiway valve 18. If the second 5/2multiway valve 1 8 is now in its second switching position, then compressed air from the compressed air supply line 1 6 is conveyed through the third input S,8 and the first output A,8 to the working piston 11 which is thereby set in motion. Thus, a signal only exists at the load port 23 when the time period t, between the signals from the pushbuttons 13, 14 is less than a time interval t provided by the timing element 22.

Now, if at the end of case 3 as is illustrated by case 4, the actuation of the pushbutton 1 3 is interrupted only temporarily, then the first multiway valve 1 7 moves into the neutral position 1 9 as does the second multiway valve 1 8 and the load port 23 is ventilated.

Actuation of the working piston 11 is then only possible when both pushbuttons 13, 14 are moved back into their initial positions in which the lines leading to the ports Z,7 and P,7 have been ventilated and have been at least simultaneously ventilated once again.

If the control signal generated at the second pushbutton 14-as shown in case 5-arrives only after a period t3, which is longer than the time interval t determined by the timing element 22, then compressed air from the supply line 1 6 arrives through the first multiway valve 1 7 located in its second switching position 21, the timing element 22 and the second multiway valve 1 8 located in the neutral position 19, at the actuating port Y,8, whereupon the second multiway valve 18 remains in the said position even when a pressure signal is present at the actuating port Z,8 thereafter. Thus, no compressed air arrives at the working piston 11.

If a component fails (for example if a spring breaks) the control device 10 may be no longer released or only once more, but then only by correct operation of the pushbuttons 13, 14.

Fig. 3 shows a second control apparatus 30 in which the load port 23 of the control unit 1 2 is not connected directly to the working piston 11, as in Fig. 1, but to the actuating port Z3, of a third 5/2-multiway valve 31 which is of similar construction to the first multiway valve 17. Of the multiway valve 31, the first input R3, is ventilated, the second input P3, is connected to the compressed air supply line 1 6 and the third input S3, is likewise ventilated. The two outputs A3, and B31 are connected to the chambers of a double-acting working piston 32. Like references are used for the other parts which correspond to those in the control device 10 according to Fig. 1.

The method of operation of the control unit 12 is the same as in Fig. 1; unlike Fig. 1, the control unit 1 2 in Fig. 3 simply controls a 5/2-multiway valve 31 which, in its turn, controls the connections to the working piston 32 which in this instance is made doubleacting.

Claims (5)

1. A compressed air actuated control device comprising two-handed actuation for a load, such as the working piston of a machine tool, especially a press, wherein two pushbuttons, preferably 3/2-multiway valves, need to be released at least substantially simultaneously for generating a control signal, and comprising two compressed air actuated 5/2multiway valves provided with spring return each of which has one actuating port, three inputs and two outputs in which, in a neutral position, the first output A is connected to the second input and the second output is connected to the first input and the third input is blocked, whereas in the second switching position the first output is connected to the third input, the second output is connected to the second input and the first input is blocked, and in which, of the first 5/2-multiway valve, the actuating port is connected to the first pushbutton, the first input is ventilated, the second input is connected to the second pushbutton, the third input is connected to a compressed air supply line and the first output is connected through a timing element to the first input to the second 5/2multiway valve, whereas, of the second 5/2multiway valve, the second input is ventilated, the third input is connected to the compressed air supply line and the first output is connected to the load port, characterised in that, the second 5/2-multiway valve has a second actuating port associated with the spring loaded end and which is connected to the second output from the same multiway valve and that the first actuating port of the second 5/2-multiway valve is connected to the second output from the first multiway valve.

2. A control device according to claim 1 characterised in that altogether the control unit has only two 5/2-multiway valves.

3. A control device according to claim 1 or 2, characterised in that the load port is connected directly to a single-acting working piston.

4. A control device according to claim 1 or 2, characterised in that the load port is connected to the actuating port of a third 5/2-multiway valve which is of similar construction to the first multiway valve and the second input to which is connected to the compressed air supply line and the outputs from which are connected to a double-acting working piston and the first and third inputs to which are ventilated.

5. A compressed air actuated control device substantially as herein described with reference to Figs. 1 and 2 or Fig. 3 of the accompanying drawings.