Patent ID: 12222740

DETAILED DESCRIPTION OF THE INVENTION

Preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings.

Embodiment

FIG.1is a schematic diagram showing the configuration of an electric discharge machine10according to an embodiment.FIG.1shows the X, Y and Z directions in which the axis possessed by the electric discharge machine10extends. The X direction and the Y direction are orthogonal to each other in a plane, and the Z direction is orthogonal to each of the X direction and the Y direction. Note that the −Z direction is a direction in which gravity acts (gravity direction).

The electric discharge machine10machines a workpiece by electric discharge generated by applying a voltage to a gap between it and the workpiece. The workpiece is also referred to as an object to be processed. The electric discharge machine10is provided with a machine main body12, a dielectric fluid unit14, and a controller16for controlling the machine main body12and the dielectric fluid unit14.

The machine main body12includes a work-pan17for storing liquid for immersing the workpiece, and an electrode18for machining the workpiece. A table for holding the workpiece is provided inside the work-pan17. The electrode18is relatively movable with respect to this table. In a state where the workpiece and the electrode18are immersed in liquid stored in the work-pan17, a voltage is applied to the gap between the electrode18and the workpiece, and the workpiece is machined by electrical discharge generated at the gap. Sludge can be produced during this machining.

The dielectric fluid unit14supplies liquid (dielectric working liquid) used for machining the workpiece to the work-pan17. As examples of the dielectric working fluid, deionized water and suchlike can be raised. The dielectric fluid unit14may collect the dielectric working fluid discharged from the work-pan17. When the dielectric working fluid discharged from the work-pan17is collected, the dielectric fluid unit14may remove sludge contained in the collected dielectric working fluid, may adjust the liquid quality or the like of the collected dielectric working fluid, or may return to the work-pan17dielectric working fluid from which the sludge has been removed and in which the liquid quality or the like has been adjusted.

The electrode18of the machine main body12may be a wire electrode or a shaped electrode for die sinking.FIG.1shows the machine main body12in which the electrode18is a wire electrode. When the electrode18is a wire electrode, the machine main body12is provided with a supply system20for supplying the electrode18to the workpiece, and a collecting system22for collecting the electrode18that has passed through the workpiece.

The supply system20has a wire bobbin24around which an unused electrode18is wound, a torque motor26that applies torque to the wire bobbin24, a brake shoe28that applies to the electrode18braking force generated by friction, a brake motor30that applies braking torque to the brake shoe28, a tension detection unit32that detects the magnitude of tension of the electrode18, and an upper die guide34that guides the electrode18above the workpiece.

The collecting system22has a lower die guide36that guides the electrode18below the workpiece, a pinch roller38and a feed roller40that can sandwich the electrode18, a torque motor42that applies torque to the feed roller40, and a collecting box44that collects the electrode18conveyed by the pinch roller38and the feed roller40.

The upper die guide34is provided with a support portion34afor supporting the electrode18, and the lower die guide36is provided with a support portion36afor supporting the electrode18. The lower die guide36is also provided with a guide roller36bthat turns the electrode18and guides it to the pinch roller38and the feed roller40.

At the time of machining, the upper die guide34and the lower die guide36are placed in the work-pan17and immersed in the dielectric working fluid stored in the work-pan17. In addition, at least the upper die guide34out of the upper die guide34and the lower die guide36may jet clean dielectric working fluid that does not contain sludge, toward the gap between the electrode18and the workpiece. When the clean machining fluid is jetted toward the gap between the electrode18and the workpiece, the gap is filled with clean fluid suitable for machining, whereby deterioration in machining accuracy due to sludge generated in accordance with machining can be reduced.

FIG.2is a diagram showing the configuration of a drainage mechanism50of the electric discharge machine10. The drainage mechanism50is a mechanism for draining the liquid stored in a liquid tank52. The liquid tank52may be the work-pan17. When the dielectric fluid unit14collects the dielectric working fluid, the liquid tank52may be a dirty water tank or a fresh water tank provided in the dielectric fluid unit14. The sewage tank is a tank for storing sludge-containing dielectric working fluid (sewage), and the fresh water tank is a tank for storing dielectric working fluid (fresh water) that has come from the sewage tank and passed through a filter for removing sludge.

The drainage mechanism50is provided with a drain valve54, an actuator56, a liquid level sensor58, and a control unit60.

The drain valve54is a valve for opening and closing a drain port62for draining the liquid stored in the liquid tank52. The drain port62may be provided in the liquid tank52or may be provided in a communicating portion64that communicates with the liquid tank52.FIG.2shows a case where the drain port62is provided in the communicating portion64. The drain valve54is disposed so as to cover the drain port62provided at a bottom wall64W of the communicating portion64.

The configuration of the communicating portion64is not particularly limited. InFIG.2, the communicating portion64protrudes outward from a side wall52W of the liquid tank52, and has a box-like shape in such a way that the capacity and height of the communicating portion64are smaller than those of the liquid tank52and an inner bottom surface of the communicating portion64has the same height as an inner bottom surface of the liquid tank52.

The actuator56drives the drain valve54. The actuator56drives the drain valve54in such a way that the amount of opening of the drain valve54with respect to the drain port62can vary. When the drain valve54closes the drain port62, the amount of opening of the drain valve54is 0. When the amount of opening of the drain valve54is greater than 0, the liquid stored in the liquid tank52flows out from the drain port62via the communicating portion64and falls on its own weight to a liquid-receiving portion of a drain channel66. The drain channel66supplies the liquid that has fallen into the liquid-receiving portion of the drain channel66to, for example, the dielectric fluid unit14.

The actuator56may be pneumatic, electric, hydraulic, or solenoidal one. In the case of this embodiment, the actuator56is electric one and has a servomotor56A. The servomotor56A rotates under the control of the control unit60to vary the amount of opening of the drain valve54. That is, the servomotor56A drives the drain valve54in the direction away from the drain port62(in the direction opposite to the direction of gravity) according to the rotation in the positive direction (or negative direction) to increase the amount of opening of the drain valve54. In addition, the servomotor56A drives the drain valve54in a direction (gravitational direction) of approaching the drain port62according to the rotation in the negative direction (or positive direction) to reduce the amount of opening of the drain valve54.

The liquid level sensor58detects the liquid level of the dielectric working fluid stored in the liquid tank52, and outputs a signal indicating the liquid level. The liquid level sensor58may be either contact or non-contact one. Examples of the contact liquid level sensor58include a float type, a capacitance type, an electrode type, a pressure type, a differential pressure type, etc. Examples of the non-contact liquid level sensor58include a radio wave type, an ultrasonic type, etc.

The float type is configured to convert into a level a rotation angle of a pulley connected via a wire to a float placed on the liquid surface. The capacitance type is configured to convert into a level a change in capacitance between a probe and a wall of a container. The electrode type is configured to convert into a level a change in electrical resistance between electrodes over a length corresponding to a liquid level. The pressure type is configured to convert into a level the deformation of a diaphragm due to a liquid level. The differential pressure type is configured to convert into a level a change in differential pressure between the liquid pressure and a container's internal pressure. The radio wave type is configured to emit the microwave changing its frequency, measure a difference in frequency between an incoming signal having reflected off the liquid surface and a transmission signal emitted at that time, and converts the difference into a level. The ultrasonic type is configured to measure and convert into a level the time taken for pulse ultrasound waves to reflect off a measurement object and come back.

The control unit60controls the actuator56and is provided in the controller16. During a machining halt time when machining of the workpiece is stopped, the control unit60changes the amount of opening of the drain valve54through control over the actuator56. In this embodiment, the control unit60can precisely change the amount of opening of the drain valve54by controlling the servomotor56A of the actuator56.

The higher the liquid level of the liquid stored in the liquid tank52during the machining halt time, the higher the water pressure of the liquid, resulting in that the amount of outflow increases that is the amount of liquid flowing out from the drain port62per unit time. Therefore, when the amount of opening of the drain valve54is fully opened from an initial stage of drainage, scattering and overflow of liquid falling from the drain port62to the liquid-receiving portion of the drain channel66are likely to occur in the initial stage of drainage. In addition, if the amount of opening of the drain valve54is fixed at a relatively small state from the initial stage of drainage, the drainage time is likely to be prolonged.

Therefore, the control unit60controls the actuator56in a manner so that the amount of opening of the drain valve54with respect to the drain port62increases as the liquid level detected by the liquid level sensor58decreases. This makes it possible to suppress changes in the amount of outflow, the amount of liquid flowing out of the drain port62per unit time, and as a result, it is possible to reduce scattering and overflowing of the liquid flowing out of the drain port62and at the same time to suppress the prolongation of the drainage time.

In the case of this embodiment, the control unit60is configured as a computer including a processor and a storage unit60A. The storage unit60A stores correspondence information that associates the liquid level with the amount of opening of the drain valve54.

FIG.3is a relational graph showing the relationship between the liquid level and the amount of opening. The relationship graph shows a straight line waveform W1in which the relationship between the liquid level and the amount of opening is linear, a convex curve waveform W2in which the relationship is non-linear, and a concave curve waveform W3in which the relationship is non-linear. The straight line waveform W1, the convex curve waveform W2, and the concave curve waveform W3all have a relationship in which the amount of opening increases as the liquid level decreases.

The storage unit60A stores relational expressions or tables indicating at least one relation among the straight waveform W1, the convex curve waveform W2, and the concave curve waveform W3as correspondence information. The table includes a plurality of liquid levels and the amount of opening associated with each of the plurality of liquid levels.

When the relational expressions are stored in the storage unit60A, the control unit60calculates the amount of opening corresponding to the liquid level detected by the liquid level sensor58using the relational expressions stored in the storage unit60A, and controls the actuator56in a manner so that the calculated amount of opening is obtained. Thus, in comparison with the case where the table is stored in the storage unit60A, the amount of occupation by correspondence information with respect to the storage unit60A can be reduced.

When the table is stored in the storage unit60A, the control unit60uses the table to obtain the amount of opening corresponding to the liquid level detected by the liquid level sensor58, and controls the actuator56so as to reach the obtained amount of opening. Thus, the actuator56can be controlled without calculating the amount of opening, and as a result, the load on the control unit60can be reduced.

When a plurality of relational expressions or tables are stored as correspondence information, the control unit60may control the actuator56based on the correspondence information selected from the plurality of pieces of correspondence information according to the operation of the operator or the like. Thus, even if the type of liquid tank52is changed because of, for example, replacing the liquid tank52with one for a different type of electric discharge machine10or one having a different shape, size, or the like, it is possible to reduce scattering and overflowing of the liquid flowing out from the drain port62while preventing the draining time from being prolonged.

Moreover, the control unit60may control the actuator56in manner so that the flow rate of the liquid drained from the drain port62becomes constant. For example, the control unit60controls the actuator56based on correspondence information indicating the relationship between the amount of opening and the liquid level at which the flow rate of the liquid drained from the drain port62becomes constant. When a flow rate sensor is provided at the drain port62, the control unit60may perform feedback control on the actuator56so that the flow rate detected by the flow rate sensor becomes a target value. The control unit60controls the actuator56so that the flow rate of the liquid drained from the drain port62is constant, thereby being able to suppress changes in the amount of outflow, which is the amount of liquid flowing out from the drain port62per unit time.

Modified Example

The above embodiment may be modified as follows.

For example, the control unit60may control the actuator56in such a way that the amount of opening of the drain valve54increases as the liquid level decreases by switching the driving power to be output to the actuator56according to the level of the signal output from the liquid level sensor58. In this way, the actuator56can be controlled without digital computation.

Inventions That Can be Grasped From the Above Description

The electric discharge machine (10) includes the liquid tank (52) configured to store liquid, the drain valve (54) configured to open and close the drain port (62) for draining the liquid stored in the liquid tank (52), and the actuator (56) configured to drive the drain valve (54). The electric discharge machine (10) further includes the liquid level sensor (58) configured to detect the liquid level of liquid stored in the liquid tank (52), and a control unit (60) configured to control the actuator (56) in a manner so that the amount of opening of the drain valve (54) increases as the liquid level detected by the liquid level sensor (58) decreases. This makes it possible to suppress changes in the amount of outflow, the amount of liquid flowing out of the drain port (62) per unit time, and as a result, it is possible to reduce scattering and overflowing of the liquid flowing out of the drain port (62) and at the same time to suppress the prolongation of the drainage time.

The electric discharge machine (10) may further include the storage unit (60A) in which correspondence information that associates the liquid level with the amount of opening is stored, wherein the control unit (60) may control the actuator (56) in a manner so that the amount of opening corresponds to the liquid level detected by the liquid level sensor (58). Thus, even if there is a design change or the like of the liquid tank (52), the actuator (56) can be controlled only by changing the correspondence information without changing a mechanical system, and it is easy to cope with the design change or the like of the liquid tank (52).

The liquid level may include a plurality of liquid levels. The correspondence information may be a table that includes the plurality of liquid levels; and the amount of opening associated with each of the plurality of liquid levels. Thus, the actuator (56) can be controlled without computing the amount of opening, and as a result, the load on the control unit (60) can be reduced.

The correspondence information may include a plurality of pieces of correspondence information. The storage unit (60A) may store the plurality of pieces of correspondence information, and the control unit (60) may control the actuator (56) based on correspondence information selected from the plurality of pieces of correspondence information. Thus, even if the type of the liquid tank (52) is changed, it is possible to reduce the scattering and overflow of the liquid flowing out from the drain port (62) while suppressing the prolongation of the draining time.

The control unit (60) may control the actuator (56) in a manner so that the flow rate of the liquid drained from the drain port (62) is constant. This makes it possible to suppress changes in the amount of outflow, which is the amount of liquid flowing out from the drain port (62) per unit time.

The liquid tank (52) may be a work-pan (17) configured to store the liquid for immersing the workpiece. This makes it possible to discharge liquid containing sludge generated through machining.

The actuator (56) may include a servomotor (56A). This makes it possible to precisely change the amount of opening of the drain valve (54).

EXPLANATION OF SYMBOLS

Reference Signs List

10: electric discharge machine17: work-pan52: liquid tank54: drain valve56: actuator56A: servomotor58: liquid level sensor60: control unit60A: storage Unit62: drain port