The future of servo technology

NIDEC’s technical capabilities

New servo technology supports control systems of unprecedented scale and precision

The rise of factory automation has brought many benefits to the manufacturing industry. Machining, in-factory transportation, assembly—every step of the manufacturing process continues to evolve with advances in automation technology. In this trend, control technology, which is the core of automation, has also made great progress. However, as the requirements for servo mechanisms that control robots and other automated equipment continue to increase, current control technology cannot keep up, and new breakthrough solutions are needed.

Until now, a control loop feedback algorithm called PID (Proportional Integral Derivative) control has been the main tool used to control the motion of robots and other equipment. The working principle of PID control is to calculate the difference between the desired value and the actual value of the controlled object based on the three items P (proportional), I (integral) and D (derivative), and then try to minimize the difference through the feedback process. These systems are not designed to conduct detailed testing of the controlled objects, but instead rely on continuous adjustment of control parameters through trial and error. Since it is an analog/hardware control method, it does not have issues related to responsiveness, which facilitates its wide application in many independent fields, including aircraft autopilot systems, motors, and hydraulic systems. In this way, PID control has evolved into many different forms. However, as the scale of a single control system expands and the requirements for accuracy become higher and higher, the number of controllers required also increases, making the trial-and-error process rather slow. In addition, there are even situations where PID control cannot achieve the required performance at all.

As the size of controlled objects (industrial robots, etc.) increases, PID control systems become more and more complex. There may even be situations where the system cannot achieve the required performance.

Industrial robotics is one area where PID control cannot keep up. NIDEC INSTRUMENTS, which develops and manufactures a wide range of industrial robots for various applications, including robots used to handle glass substrates for LCD panels, has experienced significant growth recently. As end products become larger and the focus turns to manufacturing efficiency, the size of the mother glass (the substrate that is cut into single LCD panels) increases year by year – the latest models can be as large as 5.5 square meters. In order for robots to handle these large, thin mother glass substrates, their movements need to be controlled with minute precision, as the slightest error risks breaking the glass. In addition, the increase in the size of these industrial robots brings many other problems; due to the lower mechanical resonance point, they are more susceptible to resonance, and their load can vary greatly depending on the load carried by the robot and the extension rate of its telescopic arm. big change. Even in the face of these problems, faster and more precise operations are an absolute necessity due to the need for higher productivity.

As industrial robots carrying LCD panels become larger and larger, PID control systems cannot control within the required specifications.

High-speed/high-precision operation of large industrial robots requires the following characteristics:

  • Closed-loop characteristics accommodate lower mechanical resonance frequencies
  • Disturbance response characteristics enable robust and stable operation by compensating for significant load fluctuations and disturbances
  • Command echo feature improves efficiency

Large industrial robots operating with high precision and speed require a control method that can isolate the above (at first sight, mutually exclusive) properties and control them individually. Since parameter-based control systems such as PID control cannot do this, engineers at NIDEC INSTRUMENTS had to develop a completely new control method based on current control theory, in which the controlled object is represented as a mathematical model and combined with a specially designed suitable algorithm. Pair for each individual object. Furthermore, by abandoning the idea of ​​an overall detailed model and instead using a coarse model combined with a perturbation observer function – ensuring robustness to the specified local bandwidth by compensating for uncertainty and variation – we successfully designed A versatile and stable control method. Furthermore, we designed the system so that the closed-loop characteristics can be freely matched to the mechanical characteristics of any chosen model. Finally, we have improved the command response characteristics of the feedforward controllers while also allowing them to be freely configured by applying feedforward compensation based on the closed-loop characteristics of the matching model.

The need for trial-and-error adjustment, speed sensing delay, and bandwidth prone to sympathetic vibrations—all these inherent problems of traditional PID control can be bypassed through NIDEC INSTRUMENTS’ model matching control servo technology.

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