With the rapid development of microelectronics and computer technology, an increasing number of new programmable logic devices with enhanced functionality have emerged, leading to the widespread adoption of robotic arm controllers for motion control applications. From a hardware implementation perspective, motion controllers can be classified based on the composition of core components in robotic arm control systems and the form of data transmission.
Classification based on the composition of core components in robotic arm controllers:
1. Microcontroller (MCU)-based technology
This approach uses 8-bit or 16-bit MCU microcontroller technology as its core, such as the MCS-51 or MCS-96 series, combined with memory circuits, encoder signal processing circuits, and D/A and A/D conversion circuits. The characteristics of this circuit design are: the overall solution is relatively simple, capable of implementing some basic control algorithms, offering a certain degree of flexibility, and providing simple human-machine interface management. Although the processing speed and computational capabilities of MCUs have significantly improved with the advancement of microelectronics technology, enabling motion controllers made with new components to achieve significantly enhanced performance, based on the current technological level, motion controllers based on MCU technology primarily target simple motion control applications. The MCU-based motion controller shown in Figure 2-27 is an MCU-based motor control system. As shown in the figure, the control system is very simple, primarily consisting of a PIC MCU, an inverter component, a motor, and a feedback unit. Its basic operating principle is as follows: the MCU controls the inverter component in the drive unit to output drive voltage and frequency to control a three-phase asynchronous AC motor. The motor's output results are transmitted to the controller via the feedback unit, enabling the controller to continuously monitor the motor's operational status. Feedback includes current feedback and position feedback, with control algorithms employing PID and field-oriented control.
2. PC-based technology
Given the rapid development, mature technology, and abundant software resources of PCs, fully leveraging PC resources and integrating their functionality into motion controllers has become a key focus of research and development worldwide. Specifically, PC NC systems are constructed on PC hardware platforms and operating systems, utilizing common software and hardware boards to build motion control systems according to the requirements of motion controllers. Since the PC bus is an open bus, the hardware architecture of the PC system features openness, modularity, and embeddability, ensuring that users can add functions to the CNC system and achieve functional personalization through the development of application software. The drawbacks of PC-based motion controllers include lower real-time performance and reliability compared to dedicated robotic arm control systems, as well as higher requirements for the programming skills of actual programmers, especially when developing high-performance motion control algorithms using PCs. Experience becomes particularly important, and the cost of the verification platform itself is also relatively high. Therefore, PC-based motion controller systems are more suitable for mid-to-high-end, multi-purpose motion system applications.
3. DSP-based technology
Since the 1990s, with the rapid advancement of microelectronics technology, digital signal processing (DSP) chips have been increasingly adopted in motion control systems due to their high-speed processing capabilities. DSP chips effectively ensure the real-time performance of complex algorithms, enabling their application in motion controllers. Currently, mainstream robotic arm controllers widely adopt DSP technology. For example, various types of robotic arm controllers from major brands on the market.
PMAC is a multi-axis controller that provides basic CNC functions such as motion control, discrete control, internal controller processing, and interaction with the host. PMAC uses a Motorola DSP56001 chip internally, whose speed, resolution, and bandwidth metrics far exceed those of general controllers. PMAC is an open motion controller.
The compatibility performance of PMAC with various products is as follows.
(1) Connection with different servo systems. Servo interfaces come in analog and digital types, enabling connection with analog and digital servo drives.
(2) Connection with different detection components. For example, connection with tachogenerators, optical encoders, gratings, and rotary transformers.
(3) Implementation of PLC functionality. It includes a software-based PLC that can be expanded to 2048 I/O ports.
(4) Implementation of interface functions. Customized according to user requirements.
(5) Communication with IPC. PMAC provides three communication methods: serial, parallel, and dual-port RAM. The dual-port RAM method enables high-speed communication between PMAC and IPC, while the serial method allows PMAC to operate offline.
(6) Configuration of the CNC system. PMAC forms the CNC system with the computer system in the form of a standard computer expansion card. It can be connected to the computer via PC-XT&AT, VME, STD32, or PCI bus interfaces.
4. Technology based on programmable logic controllers
Implementing motion controller algorithms and circuits on a programmable logic controller can enhance system integration and performance while offering significant flexibility. However, the entire system requires a large number of logic units, making programming challenging and the system expensive. Therefore, this approach is only feasible in scenarioses with relatively simple functionality and high speed requirements. The emergence of SOPC (System-on-a-Programmable-Chip) technology has provided new insights for this approach. SOPC is a special embedded processor system that can include at least one embedded core, offering flexible design options for reduction, expansion, and upgrading, along with software and hardware programmability. SOPC chips have significant advantages in terms of application flexibility and cost, making them one of the future directions for motion controller development.
