Abstract: Currently, most commercially available injection molding machine robots utilize a minimal control system consisting of a dedicated microprocessor and interface. In terms of mechanical structure, when positioning accuracy requirements are not high, timing belt drive is used, with the walking mechanism equipped with a sliding guide rail and speed controlled by a frequency converter. This paper proposes a PLC-based injection molding machine robot, fully utilizing the flexible control features of PLC. The walking mechanism is equipped with a sliding guide rail, employing helical gear and rack drive and frequency converter speed control; it is a cost-effective mechatronic device. The paper provides a relatively complete discussion of the machine from both mechanical structure and electrical control perspectives.
1 Introduction
Plastic products can be broadly categorized into four types based on their processing methods: injection molding, blow molding, extrusion molding, and calendering. Among these, injection molding products boast the widest application, the most diverse range, and the highest precision. These range from everyday household items like pots and pans and children's toys to components in precision industrial equipment. With the continuous emergence of various new polymer materials, many metal parts are gradually being replaced by these new materials. To meet the requirements of automated production for injection molding products and to ensure high quality and efficiency, it is essential to minimize human intervention. Based on this principle, many injection molding machine manufacturers have included specialized robotic arms for injection molding machines in their customer-selectable auxiliary components.
However , most existing injection molding machines do not have this device. Therefore, developing a dedicated auxiliary robot suitable for injection molding machines has become an important means and an inevitable choice to enhance the competitiveness of manufacturers' products.
2. Industry Status
Various types of robotic arms are essential equipment in automated production. Especially in hazardous environments where human safety and health are seriously threatened, using robotic arms to replace humans is of great significance.
The plastics industry in the Pearl River Delta region is highly developed, holding a leading position in China and being known internationally as the "world's factory." Currently, most of the injection molding machine robotic arms used in this industry are manufactured in Taiwan, such as the "Kingly" brand robotic arms produced by Taiwan's Kingly Corporation and the "Weideke" W255 series injection molding machine robotic arms produced by Taiwan's Weideke International Co., Ltd. , etc.
Analyzing the structure of such robotic arms, their electrical control systems generally employ a microcomputer minimum system or a single-chip microcomputer system. The robotic arm's drive system utilizes pneumatic drive, variable frequency speed control drive, and servo drive. In terms of mechanical construction, they employ a sliding rail structure with timing belt drive, or a ball gear rack structure with a sliding rail. The overall design philosophy is to utilize mature control technologies and combine mechanical parts and mechanisms as much as possible.
3. PLC-controlled robotic arm for injection molding machines
The aforementioned injection molding machine-specific robotic arms , from the perspective of robotic arm manufacturers , are expensive due to their specialized auxiliary equipment , especially when used for upgrading existing injection molding machines , which seems economically unprofitable. Therefore, injection molding machine-specific robotic arms with a "high performance-to-price ratio" have become an important choice and the greatest demand for all injection molded product manufacturers to improve product quality using existing injection molding equipment.
3.1 PLC-based control system
A PLC (Programmable Logic Controller) is a new type of industrial automatic control device developed around a microprocessor , integrating computer technology, automatic control technology, and communication technology. Its greatest advantages are its small size , powerful functionality , fast response speed, and high reliability. The control process is programmed using ladder diagrams. It can be modified at any time according to different production process requirements and is also scalable. Currently, because PLCs are professionally researched, developed, and mass-produced by world-renowned electrical control equipment manufacturers , their low production costs result in low prices. With the acceleration of global economic integration , market competition has led to further price reductions , providing favorable conditions for the widespread adoption of this control system across various industries.
3.2 Mechatronics Mechanical Transmission Mode
In today's rapidly evolving technological landscape, those who keep pace with technological advancements are likely to gain market share. Currently, all popular injection molding machine robotic arms on the market are designed using the aforementioned approach. This article extends this idea into a design pattern : a modular structure. This involves configuring relatively independent components within the system using mechanisms that offer the highest performance-to-price ratio, while still meeting the system's process requirements. For this system's structure, the horizontal axis is driven by a frequency converter motor with a reduction gear; the vertical and horizontal axes, as well as the pull-out axis, are driven by cylinders. Imported high-rigidity linear guides are used in the horizontal, pull-out, and vertical travel mechanisms. The mounting supports for the vertical and horizontal axes and the pull-out axis are made of commercially available high-rigidity aluminum alloy profiles, and the horizontal axis uses helical gear and rack transmission. In conclusion, the combination of a high-performance mechanical configuration and a high-performance control system has given rise to a highly competitive injection molding machine robotic arm.
4. Conclusion
Practice has proven that by utilizing mature PLC technology, frequency converter speed control technology, and advanced mechanical transmission components, and adopting a modular architecture, application engineers can quickly design and manufacture mechatronics equipment urgently needed for enterprise production. This becomes a powerful tool for equipment modification and upgrading, improving product quality, and participating in market competition.
