The development of a pneumatic stepping motor concept for valve based flow control during injection molding

To develop the control over mold filling during polymer melt manipulation, an alternative way of driving rotary plug valves, which were placed on mold runners, was investigated in this study. During the present investigation, the pneumatic stepping motor concept was explored by designing, fabricating, and testing a specific motor for a target injection molding base application. In order to improve the actuator performance, which is used to drive the valves, a stepping motor driven by a sequence of digital solenoid valves utilizing pressurized air was designed to enhance torque capacity and reduce energy consumption, while maintaining a fixed position for a long period of time. Similar to electromagnetic stepping motors, this pneumatic stepping motor can be driven by a simple switching circuit, which only moves one step for each driving signal without a fading rotation. This mechanism yields an effective system for speed and position control. Although the speed of pressurized air switching is limited by the response time of air solenoid valves that cause a lower rotation output speed, the holding torque and efficiency of this actuator was found to be relatively higher. By using a set of circular pistons aligned so as to actuate on axial wobble gear, the motor produced a very unique motion between the gear and rotor, causing the beneficial characteristics. In this study, the performance of the new motor was tested and compared to a similar size of electromagnetic stepping motor, as well. Thus, this study provides fundamental concepts to develop a suitable actuator for control valves in injection molding at low cost.