Robots are highly complex systems, presenting numerous design challenges in terms of mechatronics, functionality, and electrical aspects. When designing the building blocks of a robot system, it is necessary to understand these requirements and select appropriate design approaches.
Comparison of different controller designs
As we all know, the controller is the core of a robot, comprising motion controllers, internal and external communication systems, and any potential power stages. Let's elaborate on potential power stages here. This concept refers to the amount of force a robot needs to apply to its motors to move heavy objects. This force is generated by electrical energy and supplied to the motors from the power stage. This power level determines whether the robot is a high-voltage or low-voltage system.
There are two approaches to controller design: centralized and distributed. Centralized controller design integrates most of the robot's electronic modules (drive power module, servo drive module, communication module, I/O module) into the controller. Most robot manufacturers choose this design and package it as a whole for downstream manufacturers.
Distributed controller design involves moving some modules from a centralized controller to the robot's end effector operating system. This typically involves moving the servo drive module, allowing the end effector to support a wider range of sizes and providing greater flexibility in cable selection. The challenge of distributed controller design lies in the fact that the operating environment of the servo drive-related electronics is completely different from that in a centralized system, often requiring the redevelopment of parts of the system.
Safe and compact servo drive design
Industry 4.0 has introduced new guidelines and system requirements for servo drives, making it crucial for robot designers to select solutions that meet current and future servo drive needs. Modern robot servo drive power stage module designs emphasize compactness, high efficiency, and comprehensive protection – all three are indispensable.
One of the current functional safety standards for robots, IEC 61800-5-2, defines a safety function called Safe Torque Off (STO), which allows the system to safely stop the motor and prevent accidental starting. Devices like industrial robots and industrial mobile robots typically use DC-powered power stages with a power supply voltage of 48V to 60V, which imposes strong constraints on system hardware size. An MCU or other processor generates a PWM, and a three-phase power stage gate driver controls the power switch. When an STO command is received from an external device, a pulse suppression channel is activated to disconnect the power drive from the gate driver, thus implementing the safety function.
On the other hand, since power switches are involved, using SiC and GaN to improve motor control performance is entirely feasible, and can further improve the robot's power density and efficiency. This well-worn topic will not be elaborated further in robot design.
Low-latency instant messaging
Robots with more axes have higher requirements for network transmission, necessitating the use of real-time communication interfaces (such as high-speed serial interfaces or Ethernet) to achieve precise and safe motion and enable instant communication between all robot systems. It is essential that the main processor supports multiple protocols, such as EtherCAT, PROFINET, and EtherNet/IP, which saves costs, reduces board space and development workload, and minimizes latency associated with communication between external components and the host.
On the other hand, the bandwidth and latency of the PHY also significantly affect the coordination of the robot throughout its movement. Minimizing latency at the physical layer will greatly reduce the time required for the controller to collect and update data from connected devices, thus significantly improving network update time. As long as the PHY bandwidth is sufficient, reducing its latency is a very stable way to improve the synchronization of multi-axis systems.
Precision sensing design
Robot-related sensors cover a very wide range, from internal sensors such as voltage, current, motor speed, and temperature sensors to external sensors such as torque sensors, infrared sensors, 3D LiDAR sensors, vision sensors, and IMUs.
In terms of internal sensing, almost all sensors used in robots are currently temperature-sensitive elements with thermal compensation. This trend has greatly improved the stability of internal sensing applications and eliminated the potential for overheating and power consumption of motors under heavy loads. In terms of external sensing, with advancements in robotics technology, sensor fusion technology is also progressing. Combining different sensing technologies can achieve optimal results when deploying robot systems in changing environments.
summary
As the manufacturing industry becomes increasingly integrated at all levels, robots will play an increasingly important role in performing a wide variety of tasks. Robot developers need to understand the development trends in robot design to enable robots to operate accurately, safely, and cost-effectively.
