BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram showing an embodiment of the present invention; and
FIG. 2 is a timing chart showing timing and duration of an increase in output torque from a torque motor of the embodiment as shown in FIG. 1.
DETAILED DESCRIPTION
FIG. 1 is a schematic diagram illustrating an embodiment of the present invention. A wire bobbin 2 around which a wire electrode 1 is wound is driven by a torque motor 3 and is subjected to a predetermined torque directed in a reverse direction of a wire electrode feed direction. In addition, a velocity detector 4 is mounted on a rotary shaft of either the wire bobbin 2 or the torque motor 3 (in FIG. 1, an example is shown in which the velocity detector 4 is mounted on the wire bobbin 2). The wire electrode 1 fed out from the wire bobbin 2 is laid along a wire traveling path that passes through a plurality of guide rollers 14, is sandwiched between a brake roller 5 and a press roller 6, and further, passes through an upper guide 8, a work area in which a workpiece 13 is worked (initially a processing start aperture), a lower guide 9, and a guide roller 14, is sandwiched between wire take-up rollers 10a, 10b driven by a wire take-up motor 11, and finally is recovered at a wire recovery box 12. In the drawing, reference numeral 7 designates a brake motor of a brake apparatus that drives the brake roller 5. In addition, reference numeral 15 designates a controller that controls the wire-cut electric discharge machine. As in the related art, the controller 15 comprises a processor, a ROM, RAM or other such memory, control circuits of motors that drive the moving parts of the wire-cut electric discharge machine, an input/output interface, and so forth. To the controller 15 are connected the torque motor 3, the brake motor 7, and the wire take-up motor 11, all of which are controlled by the controller 15. Further, the velocity detector 4 is connected to the controller 15, such that a rotation velocity of the wire bobbin 2 detected by the velocity detector 4 is input to the controller 15.
FIG. 1 shows a state in which the wire electrode 1 is laid partway through the wire traveling path (up to just before the upper guide 8), and further, the wire traveling path along which the wire electrode is laid is indicated by the dotted line.
For example, when the wire electrode 1 is fed out in order to lay the wire electrode 1 up to the state shown in FIG. 1, and further, along the wire traveling path, if the velocity with which the wire electrode 1 is fed out is great, then the wire bobbin 2 continues to rotate due to the inertial force of the wire bobbin 2 and the wire electrode 1 is loosened by the wire bobbin 2 and departs from the wire traveling path, and further, the wire electrode 1 also departs from the plurality of guide rollers 14, 14 . . . along which it had already been laid, thus causing it to depart from the wire traveling path. If the wire electrode 1 departs from the wire traveling path it is necessary to repeat the work of laying the wire electrode 1 along the wire traveling path all over again from the beginning, which takes time and is difficult.
Accordingly, in the present embodiment the velocity of the torque motor 3 or the wire bobbin 2 is detected with the velocity detector 4, and when the velocity with which the wire electrode 1 is fed out reaches a predetermined velocity, torque is raised for a predetermined period of time, preventing slackening of the wire electrode 1. Thereafter, once the rotation velocity of the wire bobbin 2 reaches a safe level, the torque of the torque motor 3 is lowered to a normal value to control the wire electrode 1 feed-out operation.
FIG. 2 shows an operation of preventing slack of a wire electrode 1 when a drawing velocity of the wire electrode 1 is great in drawing or feeding the wire electrode 1. In FIG. 2, the upper graph represents variation of the velocity detected by the velocity detector 4 with respect to time and the lower graph represents variation of an output torque of the torque motor 3 with respect to time. Vmax is a velocity at which the wire electrode 1 departs from the wire traveling path and Vs is a set velocity at or above which an output torque of the torque motor 3 is raised by a predetermined amount. Ta represents a commanded torque that the torque motor 3 normally outputs and Tb represents a commanded torque for increasing the torque.
As shown in FIG. 2, when the wire electrode 1 is drawn or fed at or below the predetermined velocity Vs, the controller 15 commands that the output torque of the torque motor 3 be the normal torque Ta and to be held at the torque Ta. However, if the feed velocity of the wire electrode 1 is fast and the velocity detected by the velocity detector 4 exceeds the preset predetermined velocity Vs, the controller 15 raises the command torque to the predetermined value Tb, which increases the output torque of the torque motor 3, thereby increasing a tensioning force on the wire electrode 1 in the reverse direction of the drawing direction of the wire electrode 1 and preventing slack from arising in the wire electrode 1, thus preventing the wire electrode 1 from jumping the wire traveling path along which the wire electrode 1 has been laid up to that point. Thereafter, after a predetermined sufficient period of time elapses after the velocity of the wire bobbin 2 (or the torque motor 3) falls to or below the predetermined velocity Vs, the controller commands the torque motor 3 to output the normal torque Ta.
Although the predetermined velocity Vs that increases the output torque of the torque motor 3 is a value lower than the velocity at which the wire electrode 1 departs from the wire traveling path, if the predetermined velocity Vs is set to too low a value the velocity with which the wire electrode 1 can be fed out becomes too slow. Accordingly, setting the predetermined velocity Vs at close to the velocity at which the wire electrode 1 departs from the wire traveling path generally enhances usability.
As a method of setting the predetermined velocity Vs, for example, the output torque of the torque motor 3 may be set to Ta, the wire electrode 1 fed out, a minimum velocity at which the wire electrode 1 is loosened from the wire bobbin 2 and departs from the wire traveling path obtained by signals from the velocity detector 4, and this minimum velocity set as the velocity Vmax at which the wire electrode 1 departs from the wire traveling path. Then, a torque increase command is output from the controller 15 to the torque motor 3, a lag time and the like until the actual torque motor 3 output torque increases taken into account, and a velocity slower than the velocity Vmax at which the wire electrode 1 departs from the wire traveling path set as a provisional predetermined velocity Vs'. Then, an experiment is carried out in which the wire electrode 1 is fed out at the usual velocity at which the wire is usually fed out, the output torque of the torque motor 3 switched from the normal torque Ta to the raised torque Tb when the provisional predetermined velocity Vs' is detected by the velocity detector 4, and it is confirmed whether or not the velocity detected by the velocity detector 4 exceeds the velocity Vmax at which the wire electrode 1 departs from the wire traveling path. In this experiment, if the velocity detected by the velocity detector 4 exceeds Vmax when the wire is fed out at the usual feed velocity (the wire electrode 1 departs from the wire bobbin 2), then the provisional predetermined velocity Vs' is lowered further. That provisional predetermined velocity Vs' detected by the velocity detector 4 at which the wire electrode 1 does not come lose from the wire bobbin 2 at the velocity at which the wire electrode 1 is fed out during normal operation and does not exceed the velocity Vmax at which the wire electrode 1 departs from the wire traveling path identified as described above, is then set as a reference predetermined velocity Vs that raises the output torque of the torque motor 3.
In addition, the wire electrode 1 may be prevented from departing from the wire bobbin 2 and departing from the wire traveling path by setting the predetermined velocity Vs at a velocity smaller than the velocity Vmax at which the wire electrode 1 departs from the wire traveling path by a predetermined amount and adjusting the torque Tb raised by the torque motor 3.
Moreover, the period of time for which the output torque of the torque motor 3 is maintained at the greater torque Tb is set to a period of time sufficient to allow the velocity of the wire bobbin 2 to decrease to the predetermined velocity Vs. Alternatively, however, instead of setting a fixed period of time for which the torque Tb is maintained, the torque Tb may be maintained until the velocity detected by the velocity detector 4 falls to or below the predetermined velocity Vs after the output torque of the torque motor 3 is raised to torque Tb. The return of the output torque of the torque motor 3 to the normal torque Ta may be accomplished after the wire electrode 1 feed velocity falls to or below the predetermined velocity Vs. Therefore, for example, the torque Tb may be maintained until the velocity detected by the velocity detector 4 falls to “0”.
Patent Application
20080053963
