DE1194079B - Servo device for controlling the displacements of an electrode in an electrical discharge machine - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

HOSb

German class: 21h-30/02

Number: 1194 079

File number: A 30140 VIII d / 21h

Filing date: August 22, 1958

Opening day: June 3, 1965

Servomechanisms are already known for controlling the displacements of an electrode in an electrical discharge machine. These servo mechanisms have one sliding in a cylinder and differential pistons used to control the electrode displacements, their displacements cause unequal and opposite volume changes in two working chambers, whereby a hydraulic circuit emits a liquid under constant pressure Comprises pump, this liquid being directed through a first line into that working chamber, the changes in volume which are smaller in relation to the displacements of the differential piston learns, wherein a second line is provided that the connection between the first Line and the other working chamber to produce, this second line one narrowed passage and, downstream of the same, a passage with adjustable lights Has width, thanks to which the liquid can be drained under pressure, this passage with adjustable clearance is controlled by a device based on the electrical operating conditions the machine responds.

Such servo mechanisms have the advantage that they respond very quickly. If those Servomechanisms are out of order and the piston is due to its own weight or an effect coming from outside shifts, there is a negative pressure in one of the two working chambers, which favors the entry of air into this chamber. Given the compressibility the air, which gives rise to poor servomechanism accuracy, forms such an air inlet a major disadvantage. In addition, it is difficult to move the piston by hand, because the clear width of the narrowed passage and that of the passage with adjustable inside width are very small, so that a considerable amount of force is required to cause the fluid to flow through the passages mentioned.

These disadvantages are substantially eliminated according to the invention in that two automatically Acting valves are provided, which are open in the idle state and serve to drain to allow each of these two working chambers, and that on the other hand, the different parts of the Pistons that protrude from a cylinder, each reach through a chamber that with the liquid medium is filled and with

Servo device for the control

the displacements of an electrode in a

Electrical discharge machine

Applicant:

Ateliers des Charmilles S. A., Geneva (Switzerland)

Representative:

Dipl.-Ing. D. Jander, patent attorney,

Berlin 33, Hüttenweg 15

Named as inventor:

Nicolas Mironoff, Geneva (Switzerland)

Claimed priority:
Switzerland from August 26, 1957

is connected to a container located at a higher level.
The automatically acting valves can be spring-loaded valves, the spring striving to open the valve against the action of the fluid pressure generated by the pump. The arrangement can be such that the passage with adjustable clear width and the two automatically acting valves are arranged on the bottom of a liquid container. The automatically acting valves can also be electromagnetically controlled valves which are closed at the same time as the pump, which is to deliver the liquid under pressure, is started.

The drawing illustrates by way of example and schematically an embodiment of the invention Servomechanism.

F i g. 1 is a schematic of an electrical discharge machine;

F i g. Figure 2 illustrates the servomechanism of this machine in section.

The in Fig. The schematic of an electrical discharge machine illustrated in Figure 1 shows that the machine has a power generator, the terminals α and b of which are connected partly to an electrode E and partly to a workpiece P, both of which are immersed in a dielectric liquid. The power generator supplies the energy required to generate a series of electrical spark discharges between the workpiece P and the electrode E. Every spark lifts some metal off

509 578 / 29S

3 4

Workpiece. A servomechanism S is used to .. those that are due to the inertia of the liquid in the electrode E in the direction of the workpiece P to the line 8, which push, to the extent that the loading changes in quantity in of line 8 arise,
working of the same progresses. Both ends of the cylinder 3 are closed by an electrical The control of the servomechanism takes place 5 pieces 26 and 27, which a Bohrtrisch via a device B, which has the voltage hole 28 and 29, which has a seal between the electrode E and The work piece P is provided and in which the rod 2 slides, measures and supplies the servomechanism with a control current depending on the voltage. space 30 and 31, which is connected to the container 6 a in the in F i g. 2 in which the fluid flows through the servomechanism comprising a differential piston, the line 32 being shown in detail. As can be seen, the ben 1, which is frictionally connected to a rod 2, is connected to the two cavities 30 and 31 by one in the wall, which on each side of the same has a pipe 33 of different diameter provided at the end of the cylinder 3. The electrode £ in connection with each other. The container 6 a is something is not through a. device shown at 15 higher than the cavities 30 and 31, so that this lower part of the rod 2 is attached. The differentiation latter are constantly filled with liquid, the tialkolben slides in a cylinder 3, thereby un- is below a certain level by the level in the container 6 a like and opposite Volumenver- pressure. The rod 2 goes with changes in play in two working chambers 4 and 5 her- through a borehole 34 and 35, which are called in front. The hydraulic circuit is provided around each of the mentioned pieces and includes a container 6 which feeds a pump 7 which is intended to release control fluid between each of the mentioned cavities 30 and 31 under constant pressure and to supply the adjacent working chamber 4 and 5, respectively. This liquid is arranged above a first one.

Line 8 sent into the working chamber 5. The device described works as follows: second line 9 connects first line 8 with 25. Pump 7 pressurizes the liquid and the other working chamber 4. This second line 9, this pressure is transferred to chamber 5. The has a narrowed passage 10 and downstream of the pump dispensed liquid flows through downwardly with respect to the same a passage 11 with the constricted passage 10, whereby a pressure adjustable inner width, through which the flow arises, so that the pressure in the line 9 liquid can be drained. The from the 30 and the chamber 4 is lower than in the line 8 passage 11 outflowing liquid pours into and into the chamber 5. The container 6 α by the pump and then passed through an overflow pipe 6 b then flows through the passage the container 6. This passage 11 with an adjustable passage 11 with an adjustable internal width, in which clear internal width, consists of a ball 12, which again creates a pressure drop. As a result of the pressures prevailing on the electrical lines 8 and 9 with the aid of a finger 14, the valves 18 and 20 responding to the operating conditions of the machine are closed to a greater or lesser extent against the action of their spring device 15 in their 19 and 21 respectively. It is obvious that a piece 13 provided seat can be approximated to the pressure in the chamber 4 through the clear width. This device 15 is not described in detail with regard to the passage 11 with an adjustable clear width, since it does not belong to the invention. 40 is true. If at a given opening this

, The line 9 also has a passage, passage the ratio of the pressures in the chamber

its clear width with the help of a drill 4 and 5 equal to the inverse ratio

Hole 17 accessible screw 16 from the outside of the effective surfaces of the differential piston in

can be provided. This line can be connected to these chambers 4 and 5, so there is a

holder 6 α in connection, namely 45 state of equilibrium, and the piston moves

thanks to a passage that is not automatic if you take the weight of the bar 2

Valve 18 can be closed, which one and the electrode E neglect. If

Action of a spring 19 is exposed, which endeavors at this moment the ball 12 of her

is to open it. The line 8 can also move away with the seat, so the pressure in the chamber 4 increases

the container 6 α are in connection, on its 50 from, resulting in a displacement of the piston 1 after

Bottom a second automatic valve 20 provided above leads. Closing the passage 11 through

which is subjected to the action of a spring 21, the ball 12 causes a movement in the

which strives to open it. opposite direction. By operating the screw

To ensure a constant 16, the discharge resistance of the line 9

Pressure in the chamber 5, the line 8 has a 55 change and so the speed with which the

Set the relief valve to which a valve needle 22 servomechanism should respond,

includes, which is exposed to the action of a spring 23 when lifted from the workpiece P material

is which tends to be against a seat 24, the distance between increases

to press. The relief valve can be connected to the workpiece P and the electrode E, which is

. Screw plug 25 attached and removed 60 increase the breakdown voltage between them

the. When the liquid parts sent into the line 8 and thus the mean voltage at the

If the speed exceeds a certain pressure, the capacitor jams. The device B

it pushes the valve needle 22 against the action and sends a into the device 15

the spring 23 so that they flow out and through the current that the displacement of the finger 14 after

Line 66 can return to container 6. 65 below causes. This results in a reduction in size

The relief valve is as close as possible to passage 11 and an increase in pressure

at the narrowed passage 10 and when working in the chamber 4, which leads to the displacement of the rod 2

chamber 5, so that the pressure fluctuations are avoided and thus the electrode E in the direction of the work-

Piece P leads. Because the distance between the electrode and the workpiece is reduced, the mean voltage between the electrode E and the workpiece P decreases, so that the finger 14 returns to its starting position and the pressure in the chamber 4 is again given that value leads to no displacement of the differential piston 1. It is easy to understand that if the distance between the electrode E and the workpiece? For example, as a result of the accumulation of conductive dust, the servomechanism would react in reverse and lead to the removal of the electrode E from the workpiece P.

During operation of the servomechanism, liquid flows from the chambers 4 and 5 into the cavities 30 and 31 provided in the pieces 26 and 27 very small clearance of a few hundredths of a millimeter is provided. Since, moreover, the clear width between these boreholes and the rod 2 remains the same, the small fluid losses from the chambers 4 and 5 do not interfere with the operation of the servomechanism in any way. Rather, this arrangement has the advantage that the seals are not exposed to the relatively high pressure prevailing in the chambers 4 and 5, but only to the very weak pressure of the liquid contained in the container 6 α.

After completion or interruption of the processing, the pump 7 is switched off so that the liquid in the lines 8 and 9 and the chambers 4 and 5 is no longer under pressure. The automatic valves 18 and 20 then open under the action of their spring 19 and 21, so that the chambers 4 and 5 are directly connected to the container 6 a . The "rod 2 can then very easily be moved by hand, because the connection of the chambers is made 4 and 5 with the container 6 a through conduits suffer only very small pressure losses. This is further avoided that during the displacement of the rod 2 air enters chambers 4 and 5 by hand.

As soon as the pump 7 is put back into operation, the valves 18 and 20 are characterized in that the fluid is pressurized, closed so that the servomechanism is operational again is.

Of course, numerous modifications could be envisaged and the automatic valves could be placed in different locations. One of the valves could e.g. B. be housed in the differential piston so that it puts the two working chambers in direct connection with each other when the pressure is practically zero. This valve would have to be set so that it closes automatically when the pressure in chamber 5 becomes greater than that in chamber 4. The second valve could be placed either on line 8 or on line 9 so that one of these lines can be used is in communication with the container 6 a. In a modification, the automatic valves could also be replaced by electromagnetically controlled valves which would be closed at the same time as the pump 7 is started up.

The valves 18 and 20 could also be replaced by other elements, e.g. B. by automatic Slides through which the chambers 4 and 5 could be opened.

Claims (4)

Patent claims: 1. Lowering device for controlling the displacement of an electrode in an electrical discharge machine with a differential piston in which the displacements of the piston are unequal and opposite to each other in volume changes cause in two working chambers, and with a pump that a liquid underneath releases constant pressure and this in a hydraulic circuit through a first Line pushes into the working chamber, with a second line serving the first line to connect to another working chamber, and has a passage with adjustable width, through which the liquid can be drained under pressure and that from a device is controlled, which responds to the electrical operating conditions of the machine, characterized in that two automatically acting valves are provided which are open in the idle state and serve to to allow each of these two working chambers to be emptied, and that on the other hand through the various parts of the piston that protrude from a cylinder (3) Reach through a chamber that is filled with the liquid medium and open with a higher level container is connected. 2. Lowering device according to claim 1, characterized in that the automatically acting Valves are spring-loaded valves (18, 20), the spring (19 or 21) tending to the valve to open against the effect of the liquid pressure generated by the pump (7). 3. Lowering device according to claims 1 and 2, characterized in that the passage (11) with adjustable clear width and the two automatically acting valves (18, 20) are arranged on the bottom of a liquid container (6 a) . 4. Lowering device according to claim 1, characterized in that the automatically acting Valves are electromagnetically controlled valves that operate simultaneously with the start-up the pump (7), which is to deliver the liquid under pressure, must be closed. Considered publications:
Austrian Patent No. 189 894;
U.S. Patent No. 2,784,619. 1 sheet of drawings 509 578/298 5. 65 © Bundesdruckerei Berlin