Patent Description:
In the field of machining using a wire electrical discharge machine, there is known a technique for suppressing the occurrence of wire breakage by changing the machining conditions when the number of breakages of the wire electrode exceeds a predetermined number (for example, <CIT>).

<CIT> discloses a wire disconnection position detecting apparatus according to the preambles of claims <NUM> and <NUM>. The apparatus is configured to, after detection of a disconnection position, display the disconnection position and the possible causes of disconnection at the disconnection position.

There are various causes of breakage of the wire electrode. However, there are cases where adjustment of machining conditions is not needed such as wear of parts and temporary disturbance of the wire traveling system. If unnecessary adjustments of machining conditions are performed, the production efficiency may decrease instead due to lowering in machining speed and the like.

It is therefore an object of the present invention to provide a wire electrical discharge machine and a method of adjusting machining conditions, which can prevent a decrease in efficiency due to the unnecessary adjustments of machining conditions.

According to a first aspect of the present invention and a second aspect of the present invention, a wire electrical discharge machine and a machining condition adjustment method are set forth in independent claims.

According to the present invention, it is possible to prevent a decrease in efficiency due to the unnecessary adjustment of the machining conditions.

The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.

The wire electrical discharge machine and the machining condition adjustment method according to the present invention will be detailed below by describing a preferred embodiment with reference to the accompanying drawings.

<FIG> is a view schematically showing a configuration of a wire electrical discharge machine <NUM> according to the present embodiment. The wire electrical discharge machine <NUM> is a machine tool that performs machining (also referred to as electrical discharge machining) on a workpiece W by applying voltage to a gap (also referred to as an electrode gap) formed between a wire electrode <NUM> and the workpiece W to generate electrical discharge.

The wire electrode <NUM> is made from, for example, tungsten-based, copper alloy-based, brass-based metal or the like. The workpiece W is made from, for example, metal materials such as iron-based material or superhard material. Here, the workpiece W is supported by an unillustrated table that can move along a plane intersecting the wire electrode <NUM>. The table is moved by unillustrated motors driven by a control device <NUM>.

The wire electrical discharge machine <NUM> includes a transport mechanism <NUM> (transport device) that transports the wire electrode <NUM> along a predetermined transfer path C. The wire electrical discharge machine <NUM> further includes a tension detector (breakage detector) <NUM> for detecting the tension of the wire electrode <NUM>, a tip detection electrode <NUM> for detecting the tip of the wire electrode <NUM>, and the control device <NUM> for controlling the operation of the entire wire electrical discharge machine <NUM>.

The transport mechanism <NUM> includes, in the following order from the upstream to the downstream in the transfer path C: a wire bobbin <NUM>; guide rollers <NUM> and <NUM>; a brake roller <NUM>; a guide roller <NUM>; an upper pipe <NUM>; an upper wire guide (upper wire guide unit) <NUM>; a lower wire guide (lower wire guide unit) <NUM>; a lower pipe <NUM>; a pinch roller <NUM>; a feed roller <NUM> and the like.

The transport mechanism <NUM> automatically performs wire feeding and conveys the wire electrode <NUM> along the transfer path C under the control of the control device <NUM> when the wire electrode <NUM> is broken or other cases. The wire feeding is a process whereby the wire electrode <NUM> wound on the wire bobbin <NUM> is fed along the transfer path C, passed through the upper wire guide <NUM>, the workpiece W to be machined, the lower wire guide <NUM> and others, and held between the pinch roller <NUM> and the feed roller <NUM>. When the wire electrode <NUM> is fed, a predetermined tension is applied to the wire electrode <NUM>.

The transport mechanism <NUM> also conveys the wire electrode <NUM> after wire connection along the transfer path C, for example, during electrical discharge machining. Now, each component included in the wire electrical discharge machine <NUM> will be described along the transfer path C.

The long wire electrode <NUM> is wound on the wire bobbin <NUM>, and supplied from the wire bobbin <NUM>, then stretched around the guide rollers <NUM> and <NUM>, the brake roller <NUM>, and the guide roller <NUM>, to be sent to the upper pipe <NUM>. The wire electrode <NUM> sent to the upper pipe <NUM> passes through the inside of an insertion hole 50a of the upper pipe <NUM> to proceed downstream (downward), and is sent to the upper wire guide <NUM>. Then, the wire electrode <NUM>, sent to the upper wire guide <NUM>, passes through a machining start hole Wh or a machining groove Wg of the workpiece W placed between the upper wire guide <NUM> and the lower wire guide <NUM>, and further sent downstream (downward) toward lower wire guide <NUM>. The wire electrode <NUM> reaching the lower wire guide <NUM> passes through the inside of an insertion hole 56a of the lower pipe <NUM>, and is then collected by the pinch roller <NUM> and the feed roller <NUM> which hold the wire electrode <NUM> therebetween.

The wire bobbin <NUM> is turned by the torque given from a motor M1 having an encoder EC1. The motor M1 is driven under the control of the control device <NUM>. When the wire electrode <NUM> is broken, the motor M1 rotates the wire bobbin <NUM> under the control of the control device <NUM> to rewind the wire electrode <NUM>. The encoder EC1 measures the rotary position of the motor M1.

The guide rollers <NUM> and <NUM> deflect the transfer direction of the wire electrode <NUM> delivered from the wire bobbin <NUM> and guide the wire electrode <NUM> toward the brake roller <NUM>.

The brake roller <NUM> is turned by the torque given from a motor M2 having an encoder EC2. The motor M2 is driven under the control of the control device <NUM>. A braking force can be applied to the wire electrode <NUM> by changing the torque applied to the brake roller <NUM>. The brake roller <NUM> changes the transfer direction of the transported wire electrode <NUM>. The brake roller <NUM> in this embodiment feeds and deflects downward the wire electrode <NUM> being conveyed in a predetermined direction. The brake roller <NUM> applies a braking force caused by friction to the wire electrode <NUM> to move the wire electrode <NUM> without causing a slippage. As a result, the wire electrical discharge machine <NUM> can accurately recognize the delivered amount of the wire electrode <NUM> based on the amount of rotation of the brake roller <NUM>.

When the wire electrode <NUM> is broken, the motor M2 rotates the wire bobbin <NUM> under the control of the control device <NUM> to rewind the wire electrode <NUM>. The encoder EC2 measures the rotary position of the motor M2.

The tension detector <NUM> is a sensor that is arranged in the transfer path C between the brake roller <NUM> and the guide roller <NUM> to detect the tension of the wire electrode <NUM>. The tension detector <NUM> can also provide a function as a wire breakage detector for detecting a breakage of the wire electrode <NUM> because a break of the wire electrode <NUM> can be known by detecting the change of the tension of the wire electrode <NUM>. Hereinafter, the tension detector <NUM> is also referred to as a wire breakage detector.

The guide roller <NUM> guides the wire electrode <NUM> sent out from the brake roller <NUM> to the insertion hole 50a of the upper pipe <NUM>.

The tip detection electrode <NUM> is provided between the upper pipe <NUM> and the upper wire guide <NUM> in the transfer path C.

The tip detection electrode <NUM> detects the leading end of the wire electrode <NUM> formed due to its breakage. The tip detection electrode <NUM> moves into contact with the wire electrode <NUM> under the control of the control device <NUM> when the tension detector <NUM> detects a breakage of the wire electrode <NUM>. The tip detection electrode <NUM> in the present embodiment is movable in a direction perpendicular to the transfer direction of the wire electrode <NUM>, is located at a retracted position away from the transfer path C during electrical discharge machining, and moves to a position where the tip detection electrode <NUM> touches or crosses the transfer path C. Thereby, the tip detection electrode <NUM> contacts the wire electrode <NUM> when the wire electrode <NUM> exists at the position where the electrode <NUM> has moved.

The tip detection electrode <NUM> is connected to a voltage sensor and a power supply unit (not shown). If the tip detection electrode <NUM> is not in contact with the wire electrode <NUM>, the voltage of the tip detection electrode <NUM> remains equal to the voltage of the power supply, and if the tip detection electrode <NUM> touches the wire electrode <NUM>, a current flows between the tip detection electrode <NUM> and the wire electrode <NUM>, and the voltage of the tip detection electrode <NUM> becomes a value different from the voltage of the power supply unit. Thereby, it is possible to detect the touch of the wire electrode <NUM> to the tip detection electrode <NUM>. Thus, while the wire electrode <NUM> is broken if the tip detection electrode <NUM> moves toward the transfer path C and comes into contact with the wire electrode <NUM> and then the wire electrode <NUM> is rewound, the position of the tip of the wire electrode <NUM> can be recognized when the tip detection electrode <NUM> moves away from the wire electrode <NUM>.

The upper pipe <NUM> is arranged downstream of the guide roller <NUM> in the transfer path C, and formed with the insertion hole 50a that allows the wire electrode <NUM> to pass therethrough. As the wire electrode <NUM> is inserted into the insertion hole 50a, the upper pipe <NUM> guides the wire electrode <NUM> downstream along the transfer path C.

The upper wire guide <NUM> is arranged in the transfer path C on the downstream side of the tip detection electrode <NUM> and on the upstream side of the workpiece W so as to transport and support the wire electrode <NUM>. The lower wire guide <NUM> is arranged in the transfer path C on the downstream side of the workpiece W so as to transport and support the wire electrode <NUM> as the upper wire guide <NUM> does.

The lower pipe <NUM> is provided downstream of the lower wire guide <NUM> in the transfer path C, and formed with the insertion hole 56a that allows the wire electrode <NUM> to pass therethrough. The lower pipe <NUM> in this embodiment horizontally sends out the wire electrode <NUM> from the lower wire guide <NUM> to the pinch roller <NUM> and the feed roller <NUM>.

The pinch roller <NUM> and the feed roller <NUM> are arranged in the transfer path C downstream of, and at the side of, the lower pipe <NUM>. The pinch roller <NUM> and the feed roller <NUM> hold the used wire electrode <NUM> therebetween and pull the used wire electrode <NUM> in the transport direction on the transfer path C. The pulled wire electrode <NUM> is collected by an unillustrated collection unit. The feed roller <NUM> is turned by the torque given by a motor M3 driven under the control of the control device <NUM>.

<FIG> is a diagram showing an example of functional blocks of the control device <NUM> in the present embodiment. The control device <NUM> includes a motors drive controller <NUM>, an electrode controller <NUM>, a position calculator <NUM>, a storage <NUM>, an adjustment unit <NUM> and others. The control device <NUM> can be configured of, for example, a processor such as a central processing unit (CPU), a memory such as a read only memory (ROM) or a random access memory (RAM), various interfaces and the like. The memory implements the function of the storage <NUM>. The processor functions as the position calculator <NUM> by executing processing using information acquired via the interfaces, a program stored in the memory and various information. The processor executes processing using programs and various information stored in the memory and provides the functions of the motors drive controller <NUM>, the electrode controller <NUM>, and the adjustment unit <NUM> through the interfaces.

During the machining, the motors drive controller <NUM> drives the motors M1 to M3 so as to feed the wire electrode <NUM> along the transfer path C with a constant tension applied to the wire electrode. Additionally, at the time of breakage of the wire electrode <NUM> during machining, the motors drive controller <NUM> drives the motors M1 to M3 so as to rewind in the direction opposite to the transfer direction the wire electrode <NUM> that lies upstream of the position (also referred to as the breakpoint) where the wire electrode <NUM> is cut in the transfer path C, and conveys the wire electrode <NUM> that lies downstream of the breakpoint in the transfer direction.

The electrode controller <NUM> controls the operation of the tip detection electrode <NUM>, and moves the tip detection electrode <NUM> to a position where the tip detection electrode <NUM> can touch the wire electrode <NUM> when the tension detector <NUM> detects a breakage of the wire electrode <NUM>.

When the tension detector <NUM> detects a breakage of the wire electrode <NUM> and the tip detection electrode <NUM> detects the wire electrode <NUM>, the position calculator <NUM> collects pulses from at least one of the encoder EC1 and the encoder EC2, from the start of rewinding of the wire electrode <NUM> up to the moment at which the tip of the wire electrode <NUM> is detected. The pulses are output from the encoder EC1 or EC2 every time the motor M1 or the motor M2 makes a certain amount of change in rotary position. The position calculator <NUM> counts the pulses.

The position calculator <NUM> calculates the amount of rewinding of the wire electrode <NUM> based on the number of pulses acquired from at least one of the encoder EC1 and the encoder EC2. The position calculator <NUM> derives the breakage position of the wire electrode <NUM> from the amount of rewinding of the wire electrode <NUM>. The breakage position is located downstream from the tip detection electrode <NUM> along the transfer path C by the rewound amount of the wire electrode <NUM>. Therefore, by calculating the rewound amount of the wire electrode <NUM>, the breakage position along the transfer path C starting from the tip detection electrode <NUM> is calculated.

The storage <NUM> stores machining conditions. The machining conditions are the machining conditions under which electrical discharge machining is performed, and include at least one of the voltage pulse pause time, the servo voltage and the feed rate of the workpiece W. The voltage pulse pause time refers to a period from the end of the application of voltage to the electrode gap to the next application of voltage. The servo voltage refers to a reference voltage for advancing the wire electrode <NUM> so as to keep the discharge interval constant during machining. The discharge interval refers to a time interval from the application of a voltage pulse to the start of discharge. The feed rate of the workpiece W indicates the moving speed of the workpiece W on the plane intersecting the wire electrode <NUM>, toward the wire electrode <NUM>. The storage <NUM> also stores the range of a predetermined section on the transfer path C. The predetermined section refers to, for example, a section between the upper wire guide <NUM> and the lower wire guide <NUM>.

The adjustment unit <NUM> sets up the predetermined machining conditions stored in the storage <NUM> for electrical discharge machining. When a wire breakage takes place during the execution of electrical discharge machining under the predetermined machining conditions and when the breakage occurs within the predetermined section, it is deduced that the breakage is attributed to the machining conditions. The adjustment unit <NUM> therefore changes the machining conditions. Since a breakage occurring due to the machining conditions is considered to be caused by the fact that the discharge energy is too high, the adjustment unit <NUM> changes the machining conditions so as to lower the discharge energy generated. Specifically, the adjustment unit <NUM> controls the power supply unit (not shown) that applies voltage across the electrode gap, and performs, at least, one of the action of extending the voltage pulse pause time, the action of raising the servo voltage, and the action of lowering the feed rate of the workpiece W, as compared to those when no wire breakage is detected.

The adjustment unit <NUM> will not make any change to the machining conditions as above when no wire breakage occurs during execution of electrical discharge machining under the predetermined machining conditions, and even when a wire breakage has occurred outside than the predetermined section.

<FIG> is a flowchart showing an example of processing by the wire electrical discharge machine <NUM> according to the present embodiment. When the tension detector (breakage detector) <NUM> detects a breakage of the wire electrode <NUM> while the wire electrical discharge machine <NUM> is performing an electrical discharge machining process in step S1 under predetermined machining conditions (step S2: YES), the control of the wire electrical discharge machine <NUM> proceeds to step S3. When the tension detector <NUM> does not detect any breakage of the wire electrode <NUM> (step S2: NO), the wire electrical discharge machine <NUM> continues the current machining process (step S1).

At step S3, the wire electrical discharge machine <NUM> stops the machining process. At this time, the motors drive controller <NUM> controls and stops the motors M1 to M3 operating so as to stop the delivery of the wire electrode <NUM> in the transfer direction and other operations.

Next to step S3, the electrode controller <NUM> controls and moves the tip detection electrode <NUM> to a position where the tip detection electrode <NUM> can contact the wire electrode <NUM> (step S4). At step S5, the position calculator <NUM> resets the counter to zero that counts the pulses from the encoder EC1 or the encoder EC2.

At step S6, the motors drive controller <NUM> controls the motor M3 and the like to wind up the wire electrode <NUM> remaining downstream of the breakage position in the transfer path C, collect the wire electrode <NUM> into the collection unit, and thus remove the wire electrode <NUM>. When the tip detection electrode <NUM> is in contact with the wire electrode <NUM> (step S7: YES) after the removal of the downstream wire electrode <NUM> (step S6), the motors drive controller <NUM> controls the motor M1 and the motor M2 so as to rewind the wire electrode <NUM> by a fixed length α (step S8). In this embodiment, the fixed length α of the wire electrode <NUM> is a length that corresponds to one pulse to be output from the encoder EC1 or the encoder EC2.

After removal of the wire electrode <NUM> downstream of the breakage position (Step S6), if the tip detection electrode <NUM> is not contacting the wire electrode <NUM> (Step S7: NO), the control of the wire electrical discharge machine <NUM> proceeds to step S13.

When the tip detection electrode <NUM> is in contact with the wire electrode <NUM> after the operation at step S8 (step S9: YES), the operations at steps S8 and S9 are repeated.

When the tip detection electrode <NUM> does not detect the contact of the wire electrode <NUM> at step S9 (step S9: NO), the position calculator <NUM> multiplies the fixed length α by the number of pulses obtained from the encoder EC1 or the encoder EC2 to calculate the rewound amount of the wire electrode <NUM> and determine the breakage position (step S10).

The adjustment unit <NUM> determines whether the breakage position calculated at step S10 belongs to the predetermined section (step <NUM>). If the breakage position is within the predetermined section (step S11: YES), the adjustment unit <NUM> changes the machining conditions as described above (step S12). After the operation of step S12, the wire electrical discharge machine <NUM> executes the operation of step S13. If the breakage position is not within the predetermined section (step S11: NO), the wire electrical discharge machine <NUM> performs the operation of step S13.

At step S13, the wire feeding operation and the procedures associated therewith are executed. The wire feeding process is automatically performed by the wire electrical discharge machine <NUM>, but may be manually performed by an operator if required.

After the process at step S13, the wire electrical discharge machine <NUM> executes a machining process (step S1).

Claim 1:
A wire electrical discharge machine (<NUM>) for performing electrical discharge machining on a workpiece (W) to be machined by applying voltage to an electrode gap formed between a wire electrode and the workpiece to generate electrical discharge at the electrode gap under a predetermined machining condition while conveying the wire electrode (<NUM>) along a transfer path (C), comprising:
a wire breakage detector (<NUM>) configured to detect a breakage of the wire electrode; and
a position calculator (<NUM>) configured to calculate the breakage position of the wire electrode in the transfer path;
characterized in that the wire electrical discharge machine (<NUM>) further comprises:
an adjustment unit (<NUM>) configured to automatically adjust the machining condition when the breakage position is in a predetermined section of the transfer path and to not perform any adjustment to the machining condition when the breakage position is not in the predetermined section,
wherein the wire electrical discharge machine (<NUM>) is configured to:
automatically execute a wire feeding operation and a machining process after the machining condition has been adjusted when the breakage position is in the predetermined section,
automatically execute a wire feeding operation and a machining process without any adjustment to the machining condition when the breakage position is not in the predetermined section, and
not execute a process before or after the wire feeding operation and before the machining process when the breakage position is not in the predetermined section.