The present invention relates to a servo-press machine that includes a drive power supply capacitor, drives a servomotor based on slide motion information, and performs a press-forming operation while converting the rotational motion of the servomotor into a vertical movement of a slide through a slide drive mechanism.
A press machine that utilizes a servomotor allows the user to easily set or select slide motion (e.g., JP-A-2003-205395). Specifically, the slide speed can be arbitrarily changed. Moreover, the slide can be stopped temporarily, and the slide motion can be reversed by reversing the rotation of the servomotor. Therefore, adaptability to press-formed products can be increased, and high-quality products can be produced.
In such a servo-press machine, a motor rotation control section controls the rotation of the servomotor based on slide motion information (motion instruction signal) set in advance. A slide drive mechanism receives rotation power generated by rotating the motor to drive the slide. As the slide drive mechanism, an eccentric drive mechanism, a link drive mechanism, and a screw drive mechanism have been known. Among these, the eccentric drive mechanism (crank mechanism or eccentric shaft structure) has been generally employed from the viewpoint of the structure or the function. The slide motion information is created as a slide position corresponding to each stroke (time or angle).
FIG. 6 shows the case of using a crank mechanism. The slide position moves downward from the top dead center (position Pu) toward the bottom dead center (position PI) along a path Rsp (i.e., slide motion information), and then moves upward toward the top dead center. The slide speed is indicated by a path Rsv.
Specifically, the slide starts to move downward at a time t0 (0.0 sec) on the horizontal axis. The slide speed is reduced immediately before a time t1 in order to achieve a soft touch. The motor torque (path Rmt) thus decreases. A forming area (time t1 to t2) then occurs. The bottom dead center is reached at a time t2, and the top dead center is reached at a time t3 (about 3.6 sec). Specifically, one stroke (production cycle) is 3.6 sec.
The motor rotational speed corresponding to the slide motion (path Rsp) shown in FIG. 6 is indicated by a path Rmr. For example, when performing a deep-drawing operation, the motor is driven at low speed in order to improve the quality. The motor is accelerated immediately after completion of forming (after the time t2) along an acceleration path Rmrin to reach a high speed (allowable maximum rotational speed Mrh).
As a measure to improve speed controllability, a device that accurately estimates the load inertia that changes during operation by calculations or the like and automatically corrects a speed control constant has been proposed (JP-A-2001-352773).
The motor torque (path Rmt) rapidly increases from the minimum value up to the time t1 at which a forming load (load) occurs to reach the forming maximum motor torque Tmh. The motor torque is reduced after completion of forming (time t2). The motor torque is then increased by a torque necessary for accelerating the rotational speed. The allowable maximum motor torque Tms indicated by a bold dotted line indicates the allowable maximum motor torque of the servomotor during forming. The capacity of the servomotor and the capacity of the motor rotation control section including a position/speed control section, a current control section, and the like are selected corresponding to the allowable maximum motor torque.
A motor drive power supply device that generates a drive power supply voltage (direct-current) based on a power supply voltage (alternating-current) has been known (e.g., JP-A-2007-282367). This type of power supply device is generally used as a power supply device of a servo-press machine. In FIG. 7, a power supply device 110 includes a rectifier circuit, a switching circuit, and the like, and generates a drive power supply voltage (direct-current) based on a power supply voltage (alternating-current) input from a power supply system 100. The power supply device 110 and a current control section 33 (that forms part of a motor rotation control section) are connected through positive and negative power supply paths 120. A capacitor 130 is connected between the positive power supply path P and the negative power supply path N. The drive current is supplied from the current control section 33 to a servomotor 7.
The load (torque Rmt) of the servo-press machine increases in the forming area (time t1 to t2), and decreases in the vertical movement areas before and after the forming area, as described above. A change in load of the servo-press machine is very large as compared with other industrial machines. Specifically, a change in load within one production cycle (one slide stroke) is large. Therefore, the capacitance of capacitor 130 is relatively large in order to achieve a drive power supply voltage (voltage Vpn) smoothing function and a buffer (capacitor) function. The capacitance of the capacitor is carefully studied and appropriately selected from the viewpoint of reducing the capacities of the power supply device 110 and the power supply system 100 and reducing cost. Specifically, the capacitor 130 discharges a large amount of power (drive power supply voltage) during forming and supplies the drive power supply voltage to the current control section 33. The induced voltage of the servomotor 7 is indicated by Vm.
When performing a high-quality forming operation, the slide speed Rsv is relatively reduced in the forming area. The slide speed is increased as much as possible over the entire area from the viewpoint of improving the productivity. Specifically, the operator performs a press-forming operation while selecting various types of slide motion (path Rsp) in a production site. However, the slide motion is not selected taking into consideration the relationship among the capacities and the characteristics of the motor rotation control section 33, the servomotor 7, the power supply system 100, the power supply device 110, the capacitor 130, and the like.
Specifically, a mismatch between the selected or set slide motion and the device functions and characteristics results in an unstable operation. Moreover, such an unstable operation may or may not occur depending the experience and the skill of the operator. Specifically, the causes of unstable operation may not be determined.
Therefore, a situation in which the operation must be stopped or the device malfunctions or breaks may occur. This results in a decrease in productivity and an increase in production cost.