The robot controller, as one of the core components of industrial robots, has a decisive impact on the performance of robots, influencing their development to a certain extent. As the core part of a robot, the robot controller is one of the key components that affect robot performance, and it has a significant impact on the development of robots.Currently, due to the significant advancements in artificial intelligence, computer science, sensor technology, and other related disciplines, research on robots is conducted at a high level, which also raises higher performance requirements for robot controllers. For different types of robots, such as legged walking robots and articulated industrial robots, the comprehensive methods of control systems vary greatly, and the design schemes of controllers are also different.Types of Robot ControllersThe robot controller is a device that controls the robot to complete certain actions or tasks based on instructions and sensor information. It is the heart of the robot and determines the quality of the robot’s performance. From the perspective of robot control algorithm processing, it can be divided into two structural types: serial and parallel.1. Serial Processing StructureThe so-called serial processing structure refers to the control algorithms of the robot being processed by a serial machine. For this type of controller, it can be further divided based on computer structure and control method into the following types:(1) Single CPU Structure, Centralized Control Method: A single powerful computer implements all control functions. In early robots, such as Hero-I and Robot-I, this structure was used. However, the control process requires a lot of calculations (such as coordinate transformations), so this control structure is relatively slow.(2) Two-Level CPU Structure, Master-Slave Control Method: The primary CPU serves as the host, responsible for system management, robot language compilation, and human-machine interface functions. It also utilizes its computational power to perform coordinate transformations and trajectory interpolation, periodically sending the computed results as increments for joint movements to shared memory for the secondary CPU to read; the secondary CPU completes all joint position digital control. The two CPUs in this system have basically no connection between their buses and only exchange data through shared memory, resulting in a loosely coupled relationship. It’s quite difficult to further distribute functions by using more CPUs. The computer system of the Motoman robot (5 joints, DC motor driven) produced in Japan in the 1970s belongs to this master-slave structure.(3) Multi-CPU Structure, Distributed Control MethodCurrently, a widely adopted two-level distributed structure consists of a host computer responsible for overall system management, kinematic calculations, trajectory planning, etc. The lower-level machine consists of multiple CPUs, each controlling the movement of a joint. The connection between these CPUs and the master control machine is through a tightly coupled bus form, which significantly improves the working speed and control performance of this structure. However, the common characteristic of these multi-CPU systems is that they adopt a functionally distributed structure tailored to specific problems, meaning each processor undertakes a fixed task. Most commercial robot controllers in the world today follow this structure.The position control part of the controller’s computer control system almost universally adopts digital position control.All the above types of controllers utilize serial machines to compute robot control algorithms, and they share a common weakness: heavy computational load and poor real-time performance. Therefore, most adopt offline planning and feedforward compensation decoupling methods to reduce the computational burden in real-time control. When the robot is disturbed during operation, its performance will be affected, making it more challenging to ensure the precision required for high-speed movements.2. Parallel Processing StructureParallel processing technology is an important and effective means to improve computational speed, meeting the real-time requirements of robot control. According to literature, the research on parallel processing technology for robot controllers mainly focuses on the parallel algorithms of robot kinematics and dynamics and their implementation. In 1982, J. Y. S. Luh first proposed the problem of parallel processing in robot dynamics because the dynamic equations of articulated robots are a set of strongly coupled nonlinear second-order differential equations, making the calculations quite complex. Improving the computational speed of robot dynamics algorithms also lays the foundation for implementing complex control algorithms such as torque computation methods, nonlinear feedforward methods, and adaptive control methods.One of the ways to develop parallel algorithms is to modify serial algorithms to make them parallel and then map the algorithms to parallel structures. Generally, there are two approaches: one is to consider the given parallel processor structure and develop the parallelism of the algorithm based on the computational model supported by the processor structure; the other is to first develop the parallelism of the algorithm and then design a parallel processor structure that supports the algorithm to achieve optimal parallel efficiency.(Source: This article is reproduced from OFWEEK. 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