Technology Update Electro mechanical actuators for plastics machinery

Electric technology represents the superior solution for industrial applications, providing important benefits such as environmental cleanliness, lower noise, less energy consumption and high efficiency. While seeking electric-based motion control solutions for key industrial applications, it is critical to have the right technology partner. In addition to understanding electric technologies and their applications, the technology partner must also have a solid foundation in hydraulics and hybrid technologies. After all an unbiased assessment of the best technology for your machine—electric, hydraulic or hybrid technology—should be based on the exact needs of the application.

Electro mechanical actuator

In recent years, there has been a tendency to favour electromechanical actuators that eliminate hydraulics and hydraulic fluid. In such electromechanical actuators, two electric motors are commonly used. A metering motor is operatively arranged to selectively rotate the feedscrew. An injection motor is used to physically translate the feedscrew within the heated barrel, either in connection with or independently of the rotation of the feedscrew.

Such electromechanical injection actuators that have been developed utilise a ball-screw. Basically, this arrangement has a screw mounted for movement relative to a nut while a plurality of balls recirculated through an endless path defined in the nut. A metering motor may be operatively arranged to rotate the screw,and an injection motor may be operatively arranged to translate the screw.

However, one problem that has been encountered lies in the ability of such apparatus to resist the bounce-back or reactionary force exerted on the ball-a springy effect that exerts a reactionary force on the ball-screw.

It would be desirable to design an electromechanical injection actuator having an injection motor optimally sized so as to be capable of injecting heated plastic material into the mould.

However, such device must also be prepared to hold the hot plastic material in the mould against the reactionary force exerted by the plastic material on the ball-screw. In some cases, it is believed that an optimally-sized injection motor may be insufficient to resist the reactionary torque exerted by the compressed load on the ball-screw, particularly after the injecting motion of the feedscrew has stopped. At the same time, it would be desirable to have an optimally-sized injection motor to keep the cost of the apparatus at a practical minimum. Accordingly, some other means of resisting the bounce-back or reactionary force exerted by the compressed plastic on the ball-screw must be found.

Blow moulding using short stroke actuator
One of the biggest European producers of customised blow moulding machines approached Moog to help develop a next generation machine using full electric motion control technology for the extrusion unit. For asymmetric parts which do not have a uniform round shape, the machine needs to adjust the wall thickness of the extruded tube. Formerly, the adjustment of the eccentricity was done by hydraulic servo actuators. However, the customer wanted to switch over to an electromechanical actuator to perform this function.

The Short Stroke Actuator is a precise, compact, robust, low inertia electro mechanical actuator capable of performing highly dynamic position control and force control. This solution maintains high efficiency during positioning even when exposed to high static forces. It is designed with robust construction and lifetime lubrication for maintenance-free operation.

A low friction technology concept enables reliable position control and force control. By using this solution, the customer was able to meet its particular neadidas