Wire Feed Mechanism of Wire Electric Discharge Machine

The present invention relates to a wire feed mechanism of a wire electric discharge machine.

A wire electric discharge machine is arranged to generate electric discharge between a wire electrode and a workpiece while the wire electrode runs under a tension, to perform machining. During electric discharge machining, the wire electrode may be undesirably broken in a workpiece. In this case, the wire electrode must be rewound and connected. Conventionally, wire electrode rewinding is performed by rotatively driving a feed reel while the feed reel is being torque-controlled by an AC motor or the like. However, even when the AC motor is driven with its output torque-controlled, its rotational speed cannot be controlled. Therefore, the feed reel rotates at a high speed and it is idling after the wire electrode rewinding is completed. As a result, a winding state of the wire electrode of the feed reel is degraded. This is inconvenient to connect the wire electrode. Disclosure of Invention

It is an object of the present invention to provide a wire feed mechanism of a wire electric discharge machine, which can rewind a wire electrode, that is broken during electric discharge machining, on a feed reel, without disturbing its winding state, and which can provide a rewinding state convenient for subsequent connection of the wire electrode.

In order to achieve the above object, the present invention comprises a clutch having clutch elements one of which is integrally coupled to the wire electrode feed reel and rotatable therewith and arranged to create a coupling torque between the clutch elements that changes in accordance with a feed voltage, and a geared motor coupled to the other clutch element of the clutch. Preferably, the present invention further comprises detecting means for detecting a breakage of the wire electrode and outputting a breakage detection signal, and control means responsive to the breakage detection signal for supplying a first predetermined voltage to firmly engage the clutch, and for supplying a second predetermined voltage to loosely engage the clutch and driving the geared motor after rotation of the feed reel is stopped.

In this manner, according to the present invention, a wire electrode feed reel is driven by a geared motor through a clutch creating a variable coupling torque between clutch elements, i.e., input and output members thereof. Therefore, during electric discharge machining, a feed voltage applied to the clutch is controlled to control the tension of the wire electrode to a predetermined value. Further, when the wire is broken, the rotating feed reel and the stopped motor are coupled through the firmly engaged clutch. As a result, rotation caused by the inertia of the feed reel and so on can be immediately stopped, and the feed reel may not idle to loosen the wire electrode. Furthermore, the wire electrode is rewound by the geared motor through the loosely engaged clutch at a predetermined torque and at a low speed. Therefore, a breakage point can be easily detected, and the electrode can be stopped at a position convenient for subsequently connecting the wire electrode.

A single figure is a schematic diagram of a wire feed mechanism according to an embodiment of the present invention.

The accompanying drawing shows a wire feed mechanism according to an embodiment of the present invention, which is adapted to be incorporated in a wire electric discharge machine. Reference numeral 1 denotes a wire electrode feed reel which is detachably fitted on a rotating shaft 4 supported by a bearing 2 in such a manner that the reel 1 is rotatable in unison with the shaft 4. A wire electrode P for machining a workpiece W is wound on the feed reel 1. Fixed to one end of the rotating shaft 4 is an output shaft 5 of a clutch 3 which is of a type wherein a coupling torque between input and output members 3a and 3b of the clutch 3 changes in accordance with a feed voltage, i.e., an excitation current. Preferably, the clutch 3 is a powder clutch with ferromagnetic particles filled between its input and output members. An input shaft 6 of the powder clutch 3 is fixed to an output shaft 7 of a geared motor M. Reference symbols R1 to R5 denote guide rollers for guiding the wire electrode P. The pair of guide rollers R2 and R3 and another pair of guide rollers R4 and R5 clamp the wire electrode P and hold it to be movable in a predetermined wire feed path. The wire electrode P is disposed to be driven by feed rollers and so on (neither are shown) to travel along the path. Reference symbol S1 denotes a breakage detection sensor which is arranged to detect a flexure of the broken wire electrode P between the feed reel 1 and the guide rollers R2 and R3, thereby detecting breakage of the wire electrode P. Reference numeral S2 denotes a breakage point detection sensor which is arranged to detect the breakage point of the wire electrode P when a breakage end of the wire electrode P passes near it while the broken wire electrode is being rewound by the feed reel. Reference numeral 8 denotes a numerical controller (to be referred to as an NC hereinafter) for controlling the rotation of the geared motor M and the feed voltage to the powder clutch 3 in accordance with signals supplied from the sensors S1 and S2.

The operation of the above wire feed mechanism will now be described.

During electric discharge machining, the NC 8 supplies a predetermined low voltage to a coil (not shown) of the powder clutch 3 and at the same time drives feed rollers and so on (neither are shown) while the geared motor M is stopped. When the wire electrode P is pulled down upon the rotation of the feed rollers, the feed reel 1 rotates together with the rotating shaft 4 and the output shaft 5 of the powder clutch 3 against a predetermined low frictional force generated between the input and output members of the powder clutch 3 to which the low voltage applied, to feed the wire electrode P to an electric discharge machining section. As a result, a predetermined tension is generated by a force of the feed rollers that drive the wire electrode P and by a predetermined low frictional force of the powder clutch 3, these forces exerting in the opposite directions from each other, and the wire electrode P travels under this tension.

When the wire electrode P is broken at the electric discharge section during electric discharge machining, a portion of the wire electrode P on the feed reel 1 side is operatively disconnected from the feed rollers. However, the feed reel 1 and so on continue to rotate by inertia and the wire electrode P flexes at a location between the feed reel 1 and the guide rollers R2 and R3. The breakage detection sensor S1 detects the flexure and generates a breakage detection output signal. Upon reception of the output signal, the NC 8 outputs a high voltage to the powder clutch 3 and firmly engages the input and output members thereof, thereby increasing the frictional force acting therebetween. At that time, the geared motor M is kept stopped, and its output shaft 7 cannot rotate unless it receives a large torque. Therefore, the output shaft 5 of the clutch connected to the shaft 7 through the input shaft 6 of the clutch 3, the rotating shaft 4, and the feed reel 1, all of which have rotated by inertia, are immediately stopped. Then, the wire electrode P clamped by the guide rollers R2 and R3 is stopped as it flexes between the feed reel 1 and the guide rollers R2 and R3. The NC 8 lowers the feed voltage applied to the powder clutch 3, loosely engages the input and output members of the clutch 3, in other words, decreases the frictional resistance of the clutch to a predetermined small value, and thereafter drives the geared motor M. As a result, the output shaft 7 of the geared motor M rotates at a low speed to rotate the rotating shaft 4 and the feed reel 1 through the loosely engaged powder clutch 3, and rewinds the wire electrode P at a predetermined torque corresponding to the low frictional force resistance of the powder clutch 3. When the breakage point detection sensor S2 detects a breakage point of the wire electrode P, the NC 8 stops the geared motor M, and the wire electrode P stops at a position that facilitates a subsequent connecting operation for it while its portion around the breakage point is clamped by the guide rollers R2 and R3.