METHOD AND DEVICE FOR CONTROLLING A RECIPROCATING ACTUATOR

A method is provided for controlling a reciprocating actuator. More particularly, it regards a method for controlling a reciprocating actuator in which the working organ of the ac- tuator is arranged to be moved in a first direction and in a second direction, and in which the actuator is connected to a hydraulic aggregate via at least a directional control valve. A device for practising the method is provided as well.

In what follows, the method and the device are explained with reference to an actuator in the form of a hydraulic working cylinder which is used for tightening bolt connections. This does not in any way mean a limitation of the scope of the set of claims as the method and device provided are usable in a number of operations.

According to the prior art, during tightening operations there is often used a pneumatically driven hydraulic aggregate which delivers pressure fluid to the pressure port of a directional control valve. The directional control valve delivers pressure fluid via its plus port to the plus side of the working cylinder or via its minus port to the minus side of the working cylinder.

A pneumatically controlled hydraulic first pilot valve shifts the directional control valve into its respective positions. A somewhat simplified circuit diagram of a prior art aggre-

gate is shown in figure 3.

When a bolt is to be tightened, for example under water where it is out of the sight of the operator, the working cylinder is controlled via a manual signal to the directional control valve in its plus direction. Fluid pressure must be supplied to the plus side until the operator is sure that the desired pressure has been worked up, after which, by means of a manual signal, the directional control valve is brought into a position in which the working cylinder is moved in its minus direction. After the operator is sure that the working cylinder has taken its minus position, the directional control valve may be shifted again.

It is obvious that a control sequence in which a delay must be included to ensure that the desired pressure or position has been achieved, results in unnecessarily long time being spent on work of this kind.

The invention has for its object to remedy or reduce at least one of the drawbacks of the prior art .

The object is achieved according to the invention through the features which are specified in the description below and in the claims that follow.

A method is provided for controlling a reciprocating actuator, the working organ of the actuator being arranged to be moved in a first direction and in a second direction, and the actuator being connected to a hydraulic aggregate via at least a directional control valve. The method is characterized by a pilot pressure from the minus port of the directional control valve via a first overpressure valve being brought to shift the directional control valve into a posi- tion which causes the working organ to be moved in its first direction, and by a pilot pressure from the pressure port via

a second overpressure valve being brought to shift the directional control valve into a position which causes the working organ to be moved in its second direction.

In a preferred method in which the actuator is constituted by a working cylinder and the working organ is constituted by a piston rod, and in which the first direction corresponds to the plus direction of the piston rod and the second direction corresponds to the minus direction of the piston rod, the method is characterized by a pilot pressure from the minus port of the directional control valve via the first overpressure valve being brought to shift the directional control valve into a position which causes the piston rod to be moved in its plus direction, and by a pilot pressure from the pressure port of the directional control valve via the second overpressure valve being brought to shift the directional control valve into a position which causes the piston rod to be moved in its minus direction.

An aspect of the method is that the first overpressure valve is brought to open at a lower pressure than the second over- pressure valve.

Another aspect of the method is that the respective pilot pressures from respectively the minus port and pressure port of the directional control valve are brought to shift the directional control valve via at least a shuttle valve or a pi- lot valve.

A device for controlling the working cylinder, in which the piston rod of the working cylinder is arranged to be moved in a first direction and in a second direction, and the working cylinder is connected to a hydraulic aggregate via at least the directional control valve, is characterized by a first pilot pipe, which is connected to the minus port of the di-

rectional control valve, being connected via a first overpressure valve to the plus pilot port of the directional control valve, a fluid pressure in the plus pilot port being arranged to shift the directional control valve into a position which causes the piston rod to be moved in its plus direction, and by a second pilot pipe connected to the pressure port of the directional control valve being connected via a second overpressure valve to the minus pilot port of the directional control valve, a fluid pressure at the minus pilot port being arranged to shift the directional control valve into a position which causes the piston rod to be moved in its minus direction.

Another aspect of the device is that the first pilot pipe and the second pilot pipe from, respectively, the minus port and the pressure port of the directional control valve are connected to a shuttle valve which is arranged to control the directional control valve.

Yet another aspect of the device is that the first pilot pipe and the second pilot pipe from, . respectively, the minus port and the pressure port of the directional control valve are connected to the shuttle valve which is arranged to control a first pilot valve, the first pilot valve being arranged to control the directional control valve.

The shuttle valve which is a compressed-air valve is arranged to be operated by means of hydraulic pressure, the shuttle valve being provided with hydraulic seals at its pilot ports.

A method and a device are provided for controlling, in an automated manner, a reciprocating actuator which is dependent on a particular pressure having been achieved before the mov- ing direction of the working organ of the actuator is reversed. The method and the device are well suited for use in

locations in which the actuator is out of sight of an operator, for example under water.

In what follows is described an example of a preferred method and an embodiment which is visualized in the accompanying drawings, in which:

Figure 1 shows a circuit diagram in which the piston rod of a working cylinder has reached its minus position;

Figure 2 shows the circuit diagram of figure 1 after the piston rod of the working cylinder has reached its plus position;

Figure 3 shows a circuit diagram of a prior art aggregate;

Figure 4 shows the circuit diagram of figure 3 in a modified embodiment ;

Figure 5 shows in section a hydraulic-pneumatic pilot valve in a first position; and

Figure 6 shows the pilot valve of figure 5 in a second position.

In the drawings the reference numeral 1 indicates a working cylinder with a piston rod Ia, the working cylinder 1 being supplied with pressure fluid to its plus side from the plus port of a directional control valve 2 via a plus pipe 4, and to its minus side from the minus port of the directional control valve 2 via a minus pipe 6.

The directional control valve 2 is supplied with pressure fluid to its pressure port via a supply pipe 8.

A first overpressure valve 10 communicates with the minus port of the directional control valve 2 via the minus pipe 6. The first overpressure valve 10 is relieved into a tank 12

via a first check valve 14 in parallel with a first choke valve 16. A first pilot pipe 18 extends from the outlet of the first overpressure valve 10 to the plus pilot port of the directional control valve 2.

5 A second overpressure valve 20 communicates with the pressure port of the directional control valve 2 via the supply pipe 8. The second overpressure valve 20 is relieved into the tank 12 via a second check valve 22 in parallel with a second choke valve 24. A second pilot pipe 26 extends from the out-o let of the second overpressure valve 20 to the minus pilot port of the directional control valve 2.

The first overpressure valve 10 is set to open at a lower pressure than the second overpressure valve 20.

When the piston rod Ia of the working cylinder 1 reaches itss minus position, see figure 1, the pressure in the supply pipe 8 and minus pipe 6 increases until the first overpressure valve 10 opens. Pressure fluid thereby flows from the minus port of the directional control valve 2 via the first overpressure valve 10 and the first pilot pipe 18 to the plus pi-o lot port of the directional control valve 2. Excess fluid is drained via the first check valve 14 which helps to maintain sufficient pilot pressure.

After the directional control valve 2 has been shifted to the position shown in figure 2, and the pressure from the supply5 pipe 8 has been directed to the plus pipe 4, the pressure in the first pilot pipe 18 is relieved via the first choke valve 16.

The piston rod Ia of the working cylinder 1 is thereby moved in its plus direction until sufficient resistance arises foro the second overpressure valve 20 to open, see figure 2. Pressure fluid thereby flows from the supply port of the direc-

tional control valve 2 via the second overpressure valve 20 and the second pilot pipe 26 to the minus pilot port of the directional control valve 2. Excess fluid is drained via the second check valve 22 which contributes to sufficient pilot pressure being maintained.

After the directional control valve 2 has been shifted into the position which is shown in figure 1, in which the pressure from the supply pipe has again been directed to the minus pipe 6, the pressure in the second pilot pipe 26 is re- lieved via the second choke valve 24.

The piston rod Ia of the working cylinder 1 shifts between the plus and minus movements as long as pressure fluid is supplied under sufficiently high pressure for the second overpressure valve 20 to open.

A prior art aggregate 30 for operating the working cylinder 1 is shown in figure 3. The aggregate 30 comprises a pneumatics part 32 for operating a pump part 34 and controlling a first pilot valve 36 via a third pilot pipe 38. The first pilot valve 36 controls the directional control valve 2 via a plus pilot pipe 40, respectively a minus pilot pipe 42. The directional control valve 2 is shown in figure 3 in an embodiment with an intermediate position and spring return, which may be advantageous in a practical embodiment.

Pressure fluid is supplied to the first pilot valve 36 from the pump part 34 via a pressure pipe 44 which is connected to an accumulator 46.

Pressure fluid flows from the pump part 34 via the supply pipe 8 to the directional control valve 2.

During operation the first pilot valve 36 and thereby the working cylinder 1 is controlled manually from the pneumatics

part 32 via the third pilot pipe 38.

In figure 4 is shown a circuit diagram which has been modified to include the principles of the method and device provided.

The first pilot pipe 18 and the second pilot pipe 26 are here extended to the two hydraulic pilot ports of a shuttle valve 50 instead of directly to the directional control valve 2.

A selector valve 52 is connected in the third pilot pipe 38 and directs, in one position, pilot air from the pneumatics part 32 directly to the first pilot valve 36 via a fourth pilot pipe 54. With the selector valve 52 in this "manual" position the aggregate 30 works as an unmodified aggregate 30.

In its second position "automat" the selector valve 52 directs the pilot air to the inlet port of the shuttle valve 50 via a fifth pilot pipe 56. From the outlet port of the shuttle valve 50 a sixth pilot pipe 58 extends to the selector valve 52, at which it communicates with the fourth pilot pipe 54 when the selector valve 52 has been set into the "automat" position.

By automatic operation the selector valve 52 is set into the "automat" position, see figure 4, in which the piston rod Ia of the working cylinder 1 is moved in the minus direction. The pilot air supplied to the shuttle valve 50 via the third pilot pipe 38, selector valve 52 and the fifth pilot pipe 56, cannot flow past the shuttle valve 50 which is closed. Pressure fluid is therefore carried via the pressure pipe 44, the first pilot valve 36 and the minus pilot pipe 42 to the minus pilot port of the directional control valve 2. Pressure fluid thereby flows from the supply pipe 8 and minus pipe 6 to the minus side of the working cylinder 1.

When the fluid pressure in the minus port of the directional control valve 2 exceeds the opening pressure of the first overpressure valve 10, pressure fluid flows via the first pilot pipe 18 to the opening port of the shuttle valve 50, whereby the shuttle valve 50 opens, directing pressure fluid via the sixth pilot pipe 58, selector valve 52 and fourth pilot pipe 54 to the first pilot valve 36. The first pilot valve 36 shifts, directing pressure fluid via the plus pilot pipe 40 to the plus pilot port of the directional control valve 2, whereby pressure fluid is carried to the working cylinder 1 via the plus pipe 4.

When the pressure at the supply port of the directional control valve 2 exceeds the opening pressure of the second overpressure valve 20, pressure fluid flows via the second pilot valve 26 to the closing port of the shuttle valve 50. Thereby the shuttle valve 50 closes to pilot air to the first pilot valve 36 which shifts and brings the directional control valve to shift back, whereby pressure fluid again flows into the minus pipe 6.

The shuttle valve 50, see figures 5 and 6, includes a valve housing 60 with sealing end walls 62 which include pilot ports 64 for hydraulic fluid. The valve housing 60 is provided with a first compressed-air port 66, a second compressed-air port 68 and a third compressed-air port 70.

In a through bore 72 in the valve housing 60 are arranged cylinder sleeves 74 near the end walls 62. For each compressed-air port 66, 68, 70 there are arranged open spacer rings 76 in the bore 72, which are arranged to hold seals 78 in position between respective compressed-air ports 66, 68, 70 in the valve housing 60.

A valve slide 82, turned down at its mid portion 80, is mova-

bly disposed in the spacer rings 76 and is arranged to be sealingly movable along the seals 78. At its end portions, the valve slide 82 is provided with hydraulic seals 84, sealing internally in their respective cylinder sleeves 74.

By adjusting the length of the cylinder sleeves 74 and spacer rings 76 and the thickness of the seals 78 to the length of the valve housing 60, a suitable pre-tensioning of the seals 78 is achieved for them to seal against compressed air both against the bore 72 and the valve slide 82.

When hydraulic fluid is directed into one of the pilot ports 64, the valve slide 82 is moved across to the opposite end wall 62 and an opening forms between the first compressed-air port 66 and the second compressed-air port 68 via the mid portion 80, the third compressed-air port 70 being closed, see figure 6. Alternatively, an opening forms between the second compressed-air port 68 and the third compressed-air port 70 via the mid portion 80, the first compressed-air port 66 being closed.

To facilitate the understanding of claim 1, the reference nu- merals from the exemplary embodiment are used also for the more general indications in claim 1. Thus, the actuator and working cylinder are both indicated by the reference numeral 1, whereas the working organ and piston rod are both indicated by Ia.