Electricity: motive power systems – Positional servo systems – Program- or pattern-controlled systems
Patent
1996-09-17
1998-07-07
Ip, Paul
Electricity: motive power systems
Positional servo systems
Program- or pattern-controlled systems
318570, 318571, 318758, 364475, 5116571, 5116577, 5116588, H02P 326, G05B 1918, G05D 1300
Patent
active
057774501
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method and apparatus for control in power failure, and more specifically, to a method and apparatus for control in power failure in such machines that a workpiece and a tool are required to move always in synchronization with each other as in gear cutting machines including hobbing machines and gear grinding machines.
BACKGROUND ART
Numerically controlled machine tools cut and shape a workpiece as desired by numerically controlling relative motion of the workpiece and tool. Some types among those machines require the workpiece and tool to be always synchronized with each other during the machining operations. A hobbing machine for gear cutting is a typical example of such machines.
FIG. 6 is a perspective view showing the concept of hobbing. The reference numerals 1 and 2 indicate a workpiece and a tool for cutting the workpiece, respectively. The workpiece 1 is rotated by a servo motor for workpiece drive and its rotation speed is thereby regulated, while a spindle motor for tool drive controls the rotation speed of the tool 2 keeping itself synchronized with the servo motor for workpiece drive. The distance between the workpiece 1 and tool 2 is controlled by another servo motor for tool feed; the tool 2 may approach to the workpiece 1 or retract therefrom.
The tool 2 is a gear cutting tool called "hob," which has a thread and several flutes (cutter flutes) running across the thread, thus providing many cutting edges along the trace of the thread. The tool 2 must be positioned in such a way that the trace of its cutting edges will coincide with the tooth trace of the workpiece 1 that is subject to hobbing. By rotating the tool 2, the cutting edges will cut into the workpiece 1 one after another. Since the cutting edges are distributed along the thread trace, the points of engagement will move forward in the axial direction of the tool 2 as it rotates. Therefore, by rotating the workpiece 1 in synchronization with that movement of the engagement points, the teeth are gradually shaped on the workpiece 1 from the addendum to the bottom. In this way, the gear cutting operation is achieved by the tool's rotation synchronized with the workpiece's rotation. After completion of the gear cutting, the tool 2 retracts from the location for engagement with the workpiece 1, driven by the servo motor for tool feed.
However, in case that a power failure has happened in the middle of a machining process, the above-described hobbing machine will encounter a problem described below. Upon power failure, both the spindle motor rotating the tool and the servo motor rotating the workpiece will slow down and stop due to the loss of electric power to the amplifiers which have controlled their rotation. In such a situation, the two motors will stop by themselves independently, in spite of being under the rotation control of the numerical control (NC). It simply means that the behavior of the spindle motor for tool drive and that of the motor for workpiece drive become asynchronous with each other until they completely stop. As such, the conventional control has no means to maintain the synchronous operation when a power failure has happened, thus causing damage to the workpiece or tool in some cases.
To solve the above problem in the case of a power failure that may happen in the middle of a machining process, the applicant of the present invention proposed a technique to retract a tool promptly from a workpiece while maintaining their synchronization. According to this proposed technique, which is disclosed in Japanese Patent Laid-open Publication No. 6-185716 (1994), the energy regenerated from a tool drive and workpiece drive motors during their deceleration is used to drive a tool feed motor in order to carry the tool away from the workpiece.
As such, this prior-art control method hastens to decelerate the tool drive motor and workpiece drive motor when the main power source is interrupted, thereby producing the regenerative energy enough to drive the motor for tool feed.
REFERENCES:
patent: 4107654 (1978-08-01), Nishijima
patent: 4263535 (1981-04-01), Jones
patent: 4445167 (1984-04-01), Okado
patent: 4484287 (1984-11-01), Gamo et al.
patent: 4490946 (1985-01-01), Tsujiuchi et al.
patent: 4584796 (1986-04-01), Yoneda et al.
patent: 4639653 (1987-01-01), Anderson et al.
patent: 4678980 (1987-07-01), Sugimoto et al.
patent: 4709509 (1987-12-01), Yoneda et al.
patent: 4714999 (1987-12-01), Kiya et al.
patent: 5012406 (1991-04-01), Martin
patent: 5070290 (1991-12-01), Iwasa et al.
patent: 5319292 (1994-06-01), Backstrand
Hanyu Shigeki
Kono Shinichi
Fanuc Ltd.
Ip Paul
LandOfFree
Method and apparatus for control in power failure does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for control in power failure, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for control in power failure will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1209767