A DOUBLED TWO-CHANNEL, PNEUMATIC CONTROL SYSTEM

Abstract: A duplicate two-channel pneumatic control system enables a flow of compressed air to be delivered to a consumer by applying two control signals essentially simultaneously. The system includes a set-up of pneumatic valves (21, 22; 21', 22'; 40, 40') and accumulators (30, 30'), wherein the set-up is adapted to monitor all valves and accumulators with respect to their correct function in each working cycle. The control system is adapted to prevent compressed air being delivered to the consumer when any of the system components malfunctions or when the control signals are applied at a time difference which is greater than a pre-selected time difference.

Description: A DOUBLED TWO-CHANNEL, PNEUMATIC CONTROL SYSTEM The present invention relates to a control system which when actuated by two essentially simultaneous control signals enables a flow of compressed air to be delivered to a consumer, such as a working cylinder or like device, of the kind defined in the preamble of Claim 1. The control signals can be established by an operator actuating a trigger signal with each of his two hands. It is necessary to construct the control system so that the control signals must be applied within a predetermined time period of each other, for instance within an interim time period of 0.5 seconds, in order to drive the working cylinder. One problem with such control systems is that all re-settable components must be monitored in each working cycle in order to ensure that the components function correctly. Furthermore, the control system must be able to prevent delivery of the flow of pressurised medium to the consumer if any of the system components malfunctions, or when the respective control signals are applied with a time spacing that is greater than the chosen time interval. It has not been possible with older technology to completely fulfil the desire to ascertain that all re-settable components function correctly in each working cycle; see DE- A-32 30 056, for instance, in this respect. Although a critical control function consists in comparing two parallel working components constantly with each other, the comparison device is not checked in each cycle and is only reset when the comparison between said components shows a malfunction. This means that the comparison device is very liable to become inoperable before of one of the two mutually compared components malfunctions. This problem has been addressed in later technology and a solution provided; see EP-A10 780 743, for instance, in this respect. However, the control system known from EP-A1-0 780 743 has certain weaknesses, which are manifested in exotic types of erroneous handling of the control system and malfunctioning in said system. In the worst of cases, these weaknesses can result in unintentional activation of the working cylinder or the like. These weaknesses are associated with the basic structural design of the control system. The European standard EN 954- 1:1996, category 4, sets out requirements that are to be fulfilled by such control systems. The object of the present invention is to provide a control system which is constructed so as to reduce the risk of the occurrence of malfunctions in the system. A further object is to provide a control system that fulfils the requirements laid down in EN 954-1:1996, category 4. The object of the invention is achieved with a control system according to the embodiment set forth in the accompanying Claim 1. Further embodiments of the invention will be apparent from the accompanying dependent Claims. According to the invention, the control arrangement/control system includes two mutually identical control units each comprising an operating device, a power valve and an accumulator. The working cylinder is supplied with compressed air from the mains through a conduit that includes the two power valves in series . The power valves are normal spring biased towards a first position in which they block the conduit. When the two operating devices are actuated generally simultaneously, for instance within a chosen time period of 0.5 seconds, for example in response to actuation from respective hands of the operator, the power valves of respective control units can be set to their second position in which compressed air is delivered to the working cylinder. The air supply to the working cylinder is stopped immediately one of the operating devices is released, wherewith the working cylinder is normally caused to return to its initial state. Each operating device includes two driven operating valves which are moved in parallel to their actuated second position with the aid of a bridge which is actuated by a control signal, for instance by an operator depressing the bridge with one hand. When said valve is in its first position, compressed air taken from the net is delivered through each power valve to a conduit that includes two branches. Each branch passes the two operating valves in respective operating devices when the two operating valves are in their first inactivated position. The accumulator is connected to one end of respective branches . When the two operating devices are switched to their second position, respective accumulators are emptied through the adjacent first operating valve, wherewith the working medium passes through a supply line to the associated power valve for switching said valve to its second position, said accumulator emptying conduit having a branch that leads to the surroundings via the second operating valve in the second operating device provided that this second operating valve has not been switched to its second position in which it blocks the branch outlet. The outlet of said branch through the second operating valve of the second control unit forms an air throttle or constriction which defines the aforesaid chosen time interim period (e.g. an interim of 0.5 seconds) together with the accumulator volume and the pressure of the compressed air source. If the second operating valve of the second control unit fails to close within 0.5 seconds of the actuation of the operating device of the first control unit, the volume of air in the accumulator will be insufficient to switch the power valve of the first control unit to its second position (and is then held in this second position). By ensuring that the volume of accumulator air that switches said power valve is enclosed (by the aforesaid blocking of the branch outlet) the enclosed air volume is able to hold the power valve in said switched position during the working cycle concerned. This obviates the need of other separate means to hold the power valve in its second position subsequent to said valve having switched to said position. To enable the function of the power valves to be controlled (e.g. to check that the power valves have been restored completely to their first positions by their respective return springs, i.e. that none of the springs has broken and that the valves have not stuck), each power valve may conveniently be designed so that the outlet of the through- passage of the power valve from the compressed air source to the accumulator supply conduit will cause compressed air to leak to atmosphere, for instance return the air from this conduit through an adjacent port in the power valve to atmosphere, already in response to a slight deviation in the movement of the power valve from its first position. This can be readily achieved in a 5/2-valve of standard design, by widening said outlet port. In practical embodiments, this leakage flow of compressed air taken from the net back through the power valve and out into the surroundings can be achieved by displacing the power valve through a distance of 1.5 mm when the total length of stroke of the valve is 9 mm between said two end-positions. If the operating valve, which in its second position empties the accumulator in a direction towards the associated power valve, has a leakage in its first position that tends to switch the power valve to its second position, there is a danger that the power valve will actually be switched because compressed air taken from the net is supplied constantly to the accumulator via the two operating valves of the operating device concerned. By restricting the replenishing flow to the accumulator from the compressed air source with the aid of means suitable to this end (for instance with the aid of one or more restrictions), the accumulator replenishing flow can be made smaller than the leakage flow that is able to switch the power valve. This flow limiting means may, for instance, comprise a restriction in respective accumulator charging branch conduits. When these flow restricting means are provided in the accumulator charging conduit or in its branches to the accumulators, said means will also prevent a "puff" of compressed air being delivered to the accumulators should only one of the power valves have been returned to its first position. The minus side of the working cylinder is subjected to pressure from the net through each of the power valves, which are then connected in parallel in their first positions. The plus side of the working cylinder is evacuated through one of the power valves, regardless of whether said valve is in its first end-position or in its second end-position. Compressed air is delivered to the minus side of the working cylinder from the net either via the first power valve (in its second position) and one supply conduit, or via the second power valve (in its second position) and the accumulator charging conduit connected to this latter supply conduit. The invention will now be described in more detail with reference to exemplifying embodiments thereof and also with reference to the accompanying drawings. Fig. 1 illustrates schematically a valve layout for a pneumatic two-hand control system according to the invention. Fig. 2 illustrates a first modification of the return of the working cylinder to its first end-position. Fig. 3 illustrates a second modification of the return of the working cylinder to its first end-position. A pneumatic two-hand control system or arrangement includes two generally identical control units 1, 1'. Since the two units 1, 1' are mutually identical, it will suffice to describe only one of these units. The unit 1 includes an operating device 20 that has two parallel operating valves 21, 22. In the illustrated case, each of these valves is provided with an associated pilot valve 11, 12 which form a pilot unit 10 and is each coupled to an operating bridge 13 so that both valves can be switched to an active state by an operator pressing down on the bridge 13 with one hand, for instance. If power amplification is unnecessary, the unit 1 can be omitted and the bridge 13 positioned so as to bridge the operating valves 21, 22. An accumulator 30 is arranged to coact with the operating device 20 so as to be emptied via the one operating valve 21 when said valve is switched, wherewith the accumulator is emptied of air through the conduit 81 and its branch 82 and therewith cause the power valve 40 to be displaced to its second position. The power valve 40 is biased to its first end-position by means of a spring 41. The plus side of a working cylinder 50 is connected to a compressed air source 60 via a conduit 90 that includes the two power valves 40, 40', said valves allowing compressed air to pass to the plus side of the cylinder 50 when in their second position. When in their first position, each of the power valves 40, 40' will function to supply compressed air from the net to the minus side of the cylinder 50, wherewith the plus side of the cylinders is evacuated to atmosphere via one, 40, of the power valves . When the operating device 20 is in its first position or state, compressed air is delivered through the power valves in their first position to a common accumulator supply conduit 72 which has a respective branch 73, 73' to an associated accumulator 30, 30', wherewith the branch 73, 73' extends through respective operating valves 22, 21. Thus, the accumulators 30 are charged when the control system is in the illustrated state. When the operating device is switched to its second position, the accumulator 30 is discharged via the conduit 81 and the conduit 82, so as to switch the power valve 40 instantaneously. The conduit branch 83 extends to the surroundings through the second operating valve 22' of the control unit 1', although this passageway through the valve 22' (in its first position) has relatively small cross- sectional dimensions and has a throttling function such that the accumulator 30 is able to hold the power valve 40 switched in its second position over at least said selected time period. The conduit 83 is closed immediately the operating device 20' is switched to its second position, thereby keeping the volume of air in the accumulator enclosed therein and enabling the power valve 40 to be kept in its second position. When the operating device 20 is switched, the accumulator 30' is emptied to the power valve 40' therewith switching said valve. The end of the conduit branch 83' is already closed, by virtue of the valve 22 being switched to its second end-position and therewith blocking its outlet port 3. It will be apparent that if the operating device 20' is switched after the chosen time period has expired, air will already have leaked from the accumulator 30 through the conduit branch 83 and via the operating valve 22' (in its first position), so that the spring 41 will have returned the power valve 40 to its first position, said valve 40 then preventing pressurisation of the plus side of the working cylinder 50 via the conduit 90, 93 from the net 60. According to one particularly preferred embodiment of the invention, the power valves 40, 40' are comprised of conventional 5/2-valves that have been modified with respect to the port 4 , which has been widened to provide a leakage facility from the port 4 to the port 1 and thus to atmosphere already when the valve 40, 40' has been displaced through only a slight distance from its first position. For instance, should the spring 41' malfunction or the valve body of the valve 40' become stuck for some reason or other or is prevented from moving to its first end-position, there is achieved a favourable effect in which the accumulators 30, 30' are each emptied via their respective operating devices 20, 20' in their first position through the conduit 73, 72 and via the malfunctioning/leaking power valve 40' and its associated conduit branch 71'. Pressurised air taken from the net 60 through the second power valve, which can be assumed to have been returned to its first position, passes through the branch conduits 71 concerned and is then able to leak out through the branch conduit 71' and the valve 40' via the leakage from the port 4 to the port 1 and from there to the surroundings. A "puff" of compressed air through the branch conduit 71 would be able to float up through the supply conduit 72 to the accumulators, although the valves 75, 75' in the conduit sections 73 will ensure that the accumulators 30, 30' cannot be charged. The accumulators are therefore evacuated relatively quickly through the conduit 71'. It will be apparent from Fig. 1 that the power valves and the operating valves of the illustrated embodiment may be conventional 5/2-path valves, which enables the two-hand control system or arrangement to be constructed with standard components. The pilot control arrangement 10 is of conventional design and is provided to enable an operator to effect switching of the two operating valves 21, 22 by exerting a small force on the bridge 13, as will be understood by those skilled in this art. Although the invention has been described above with reference to two-hand control wherewith an operator physically actuates respective bridges 13, 13' with respective hands, it will be obvious that the control signals that cause switching or resetting of the operating device 20, 20' can have other origins. It will also be understood that the illustrated working cylinder 50 can be replaced with some other energy consumer. It has been assumed in the aforegoing that the control arrangement and the working cylinder 50 in the control system are driven with compressed air taken from a common compressed air system, although it will be understood that the power valves can adjust the supply of energy to the working cylinder 50 or its technical equivalent more indirectly. It will also be understood that the operating valves 21, 22 may be physically built together with the pilot valves 11, 12 or rather together with parts of a larger valve unit, if so desired. The working cylinder 50 may include conventional flow regulating valves and safety valves, as shown in the drawing. It will be seen from the drawings that the port 1 of one power valve 40' connects with an outlet conduit 94 which opens into atmosphere, and that the conduit 90 to the plus side of the working cylinder 50 passes between the ports 2 and 1 of the power valve 40 when said power valve is in its first position, wherewith a conduit 92 connects from the port 1 of the valve 40 to the outlet conduit 94 between the port 1 and the valve 40' and the outlet of the conduit 94. The conduit 90 leading to the plus side of the cylinder 50 is also evacuated through the valve 40 when said valve is in its second position, and from there through a conduit 93 and to atmosphere through the valve 40' with said valve in its first position, and then out through a conduit 94. It will also be seen that compressed air is delivered to the minus side of the cylinder 50, i.e. the conduit 91, through each of the valves 40, 40' with said valves in their first position. Thus, it is necessary for the cylinder 50 to return or having had returned to its withdrawn position before the accumulator 30, 30' can be filled. It can be said that the inventive control system is a duplicate or duplicated two-channel pneumatic control system for controlling the flow of fluid from a fluid pressure source to a consumer, such as a working cylinder or the like. If the air leaking from the valves is greater than the volume of air that can pass through the constriction 73, 73', the pressure in the accumulator will decrease so as to prevent the power valve from being switched in a later manoeuvre. Thus, in order for the accumulators to be filled with sufficient energy to switch or reset the power valve, it is necessary for all valves to be in their first position and that no substantial leakage occurs. In order for the working cylinder 50 to be able to execute a working stroke, it is necessary for all valves to be switched and for the accumulators to contain sufficient energy for switching the power valves . It will be apparent from the drawings that when one operating device 20 is switched, its power valve 40 will be switched at least temporarily by air from the accumulator 30. Activation of the accumulator 30' of the second operating device 20' will therewith commence via the port 4 of the power valve 40 to the port 1. When the operating device 20' is switched within a chosen time period (0.5 sec), both accumulators will contain sufficient compressed air, which is enclosed in respective circuits, and be able to hold respective power valves in their switched positions. Immediately the operating device 20 of one unit 1 is released, the accumulator 30' of the other unit will be evacuated to the port 1 through the port 2 of the valve 22, so as to cause the valve 40' to return and break the supply of air to the cylinder 50. The compressed air that held the valve 40 switched is also evacuated via the valve 21, so that the valve 40 will return to its first position and break the air supply through conduit 93, 90. Figs. 2 and 3 illustrate alternative means for restoring the working cylinder 50 to its first deactivated position. Fig. 1 shows the minus chamber of the cylinder 50 coupled with a conduit 51 to the conduit 71 for evacuation through the valve 40 in its second position. In the case of the variant shown in Fig. 2, the minus chamber of the cylinder 50 is no longer connected to any part of the pneumatic two-hand control arrangement, but stands open to the surroundings, wherewith the piston of the cylinder 50 is biased towards the deactivated end-position of the cylinder by a mechanical compression spring. Fig. 3 shows a pneumatic variant of the return spring shown in Fig. 2. In the Fig. 3 embodiment, the minus chamber of the cylinder 50 is coupled to the net 60 via a conduit 95 which includes a valve 96 that closes the conduit 95 when the pressure in the minus chamber equals the net pressure. An accumulator VI6 is coupled to the conduit 95 to enable the piston of the working cylinder 50 to be returned quickly, by discharging the contents of the accumulator. The accumulator V16 includes an overpressure valve V17 which relieves the pressure when the working cylinder 50 is manoeuvred to its activated second end-position.

Claims: CLAIMS 1. A duplicate two-channel pneumatic control system for controlling the flow of pressured fluid from a pressurised fluid source (60) to a consumer (50), wherein the system includes two control units (1, 1') each of which has an operating device (10, 13, 20; 10', 13', 20'), wherein each operating device includes two separate operating valves (21, 22; 21', 22'), wherein each control unit (1, 1') has an associated accumulator (30, 30'), wherein each accumulator is adapted to be evacuated in response to actuation of the associated operating device, so as to move a respective power valve (40, 40') from its first inactivated position, towards which said valve is biased by spring means (41, 41'), to an activated second position, wherein the two power valves (40, 40' ) are coupled in a conduit leading from a compressed air source to the consumer so as to power the consumer with compressed air when both power valves are in their second positions, and wherein the system is adapted to enable the consumer to be powered solely when the two operating devices (13, 20; 13', 20') are actuated to their second positions within a predetermined time period, characterised in that the two power valves are adapted so that when in their first position, each valve will lead compressed air from the compressed air source (60) through a conduit system (71, 71'; 72; 73, 73') that includes a common conduit (72) and a respective first conduit branch (73, 73' ) which leads from said common conduit to a respective accumulator (30, 30' ) via the two operating valves (22, 21; 22'; 21') in respective operating devices (20, 20' ) when said operating valves are in their first non-activated position; in that in each control units (1, 1') the accumulator (30, 30') is adapted to be emptied via a conduit path (81, 82; 81', 82') leading to the power valve for switching said valve (40, 40') to its second position when the operating device is actuated to take its second position, wherein the conduit part includes a branch (83, 83') which includes one (22') of the operating valves in the operating device (20') of the second control unit (1'), wherein when the operating valve (22' ) in this last mentioned conduit branch (83) is in its activated second position, said valve functions to block said conduit branch so as to enable the air volume in the accumulator (30) to switch the associated power valve (40) and to hold said power valve in its switched position; and in that the passageway (81, 82; 81', 82') is adapted to be evacuated via the last mentioned conduit branch (83) and the operating valve (22') provided therein when said valve is in its non-activated first position. 2. A control system according to Claim 1, characterised by means (75, 75') for restricting the flow of replenishment air to respective accumulators to a volume that is lower than a volume corresponding to a hazardous valve leakage. 3. A control system according to Claim 1 or 2, characterised in that each of the conduit branches (83, 83' ) of the conduit path (81, 82; 81', 82') includes a constriction that defines a predetermined emptying time with respect to the associated accumulator (30, 30' ) when the operating valve (22', 22) provided in the branch is in its first position. 4. A control system according to Claim 3, characterised in that the constriction is formed by the flow passageway through the operating valve (22', 22) in the conduit branch (83, 83' ) . 5. A control system according to any one of Claims 1-4, characterised in that the operating valves of respective operating devices (20, 20') are adapted to be displaced simultaneously to their second end-position by means of a bridge (13, 13') which is coupled mechanically to said valves for simultaneous displacement thereof. 6. A control system according to Claim 5, characterised in that each operating device (20, 20') includes a pilot valve (11, 12; 11', 12') for displacing respective operating valves; and in that the pilot valves of respective operating devices are mutually connected by an actuator bridge (13, 13' ) . 7. A control system according to any one of Claims 1-6, characterised in that each power valve (40, 40' ) is adapted to allow compressed air to be delivered to the accumulator replenishment conduits (71, 71', 72) solely when the power valve is in the immediate vicinity of its first end-position; and in that the power valve (40, 40') is adapted to evacuate the replenishment conduit (71', 71, 72) and therewith the accumulators (30, 30' ) to atmosphere from and in a position slightly spaced from the first position, when the operating valves are in their first position. 8. A control system according to any one of Claims 1-7, characterised in that the consumer (50) is a working cylinder; in that the plus side of the cylinder (50) is adapted to be evacuated through either power valve (40) in its first position and via a conduit (93) serially through the other power valve (40') in its first position; and in that said one power valve (40) is also adapted to evacuate the plus side of the cylinder (50) when in its second position. 9. A control system according to any one of Claims 1-8, characterised in that the consumer (50) is a working cylinder (50) , wherein compressed air is delivered to the minus side of the cylinder partly via one power valve (40) in its first position and a supply line (91), and partly via the other power valve (40' ) in its first position and via the accumulator replenishment conduits (71', 71) that are in communication with the supply conduit (91) . 10. A control system according to any one of Claims 1-9, wherein the consumer (50) is a working cylinder (50) and wherein compressed air is delivered to the plus side of the working cylinder from the net via the two power valves in their second positions.

Inventors: SVENSSON NILS, WETZEL UWE, SVENSSON, NILS, WETZEL, UWE
Applicants: RUDOLF WESTERBERG AB, SVENSSON NILS, WETZEL UWE, SVENSSON, NILS, WETZEL, UWE
Application year: 1999
Main classification: F16P3
IPC codes: F15B20, F16P3