Development of Take-out Robot for Molding Machine with Active Vibration Control Device

1. Summary

Plastic injection molding technology is a technology for manufacturing plastic products by injecting molten resin into a mold, has many advantages such as mass production at low cost and light weight of plastic. Therefore, the technology has offered many attractive products such as home appliances, communication devices, automobiles and medical equipment. Application of take-out robots has been promoted mainly for the purpose of improving productivity of injection molding. The developed take-out robot is based on shape optimization design for speeding up. It enabled lightweight and high rigidity, the mass of the drive part was reduced by 16% and the take-out cycle time by up to 29% compared with the conventional model, resulting in 10% improvement in productivity. In addition, the robot was equipped with the active vibration control (AVC) device for the first time in the take-out robot industry. The waiting time with the AVC is shortened by up to 71% compared to that without the AVC.

2.  Outline of technology

In the operation of the take-out robot, when vibration is left during movement of the robot arm holding the workpiece, contact between the mold and the workpiece may occur. Therefore, it is necessary to provide a waiting time until the vibration converges and it leads to a decrease in productivity. We developed a take-out robot equipped with an AVC device to reduce this waiting time. Figure 1 shows the developed robot. The AVC device is mounted on the tip of the robot arm. A schematic diagram of the AVC device is shown in Fig.2. This AVC device is composed of two acceleration sensors, a control unit and a driving unit. The acceleration sensor is installed on the arm and the additional mass. These sensors measure the vibration of the robot arm, and the electromagnetic force is generated against the vibration to suppress the vibration.

Generally, the AVC using displacement feedback control is effective to the take-out robot arm. However, it is difficult to measure the arm displacement directly because of the characteristics of the take-out robot that the arm enters into the narrow mold space. Even if we estimate the displacement by integrating the acceleration measured by the acceleration sensor, this integration operation generates a drift component. Although the vibration displacement can be estimated using a filter to eliminate this drift component, a phase shift occurs. It leads to deterioration of vibration damping performance or oscillation. To solve this problem, the developed robot has a function that measures the natural frequency of the arm and carries out correction of phase shift.

Figure 3 shows the effect of AVC. The vibration quickly attenuated by active control, which enabled us to reduce the waiting time.

Fig.1 Developed take-out robot

Fig.2 Schematic diagram of the AVC device

(a)Time series wave form   (b)Trajectory

Fig.3 Effect of AVC

Atsushi Shirasaki*1

Fumitake Watanabe*2

Mitsuharu Hamahata*2

Yoshiyuki Tokuyama*2

Takayo Kotani*1

*1 Member,Yushin Precision Equipment CO., LTD(555 Kuzetonoshiro-cho, Minamiku, Kyoto 601-8205 JAPAN)

Yushin Precision Equipment CO., LTD(555 Kuzetonoshiro-cho, Minamiku, Kyoto 601-8205 JAPAN)