In automated production with a large number of industrial robots, downtime for adjusting robot positions is inevitable due to various circumstances. This process often takes several hours, and the resulting production loss is often unacceptable to customers. "Rapid deployment and easy debugging" is one of the biggest challenges faced by almost every industrial robot integrator and vendor.
In the 3C manufacturing industry, industrial robots are increasingly being used in the processing, handling, and assembly of 3C components. Due to the large production capacity demand, the most significant feature that distinguishes the 3C manufacturing industry from the traditional equipment manufacturing industry is the compact layout of each section and the short working hours. Such a short and fast pace inevitably makes it difficult to do without the cooperation of workers—even with humans supervising and leading the work, while robots assist in completing the complex physical tasks.
The above discussion points to the future development trend of robotics technology for robot integrators: a "human-centered" industrial technology development philosophy. This requires industrial robots, these emotionless and thoughtless cold metal tools, to become "soft" and capable of close interaction with humans to a certain extent, in order to truly adapt to the development requirements of future smart factories and unmanned factories. Currently, more and more robot manufacturers have noticed this and are committed to tackling key technologies such as direct teaching and human-robot collaboration.
Technical Overview
To achieve in-depth human-robot collaboration, it can be simply understood as using various technical means to make robots "softer" than rigid bodies, enabling them to sense and identify relatively small external forces during operation and produce specific responses. For example, in working mode, they should stop if an unexpected collision occurs; in teaching mode, the robot's working surface can be easily pulled to a designated position (direct teaching). The technical foundation of this technology is zero-force control technology.
Currently, there are two known implementation methods for zero-force control technology: position-based zero-force control and direct torque control-based zero-force control. The former requires the use of various force detectors or estimation methods to obtain the direction of the external force and implement corresponding compensation until the external force disappears. The latter calculates the gravity and friction forces corresponding to each joint, and the servo controller operates in torque control mode. By controlling the servo drives of each joint to output corresponding torques, the robot can overcome inertial forces and move under the action of external forces.
Current state of technology
In the earlier ISO 10218 standard, four human-machine collaboration methods were proposed, ranked from lowest to highest level of collaboration:
1. Safety-rated monitored stop
2. Handguiding
3. Speed and separation monitoring
4. Power and force limiting
Analysis of the industrial robot and equipment market reveals the following: First, foreign countries currently hold a significant lead in this field, with representative brands like KUKA and UR offering dedicated human-robot collaborative models. In contrast, my country is still in the theoretical and laboratory stages, with few mature products available. Second, all direct control methods, both domestic and international, rely on force sensors, necessitating the addition of force sensing units at the end effector or within the robot body. This inevitably increases the robot's manufacturing cost considerably.
In summary, it is imperative to develop mature zero-force control and collision detection technologies as soon as possible and apply them to industrial robot control to reduce the manufacturing, maintenance, and deployment costs of robots.
Technological Application Examples
Adhering to a people-oriented philosophy, Shenzhen Jingjiang Robotics Technology Co., Ltd. (hereinafter referred to as "Jingjiang") has been committed to the development of human-machine friendliness and human-machine collaboration technologies since its establishment, continuously applying the concept of human-machine collaboration to the industrial automation equipment it researches, develops, and manufactures. To ultimately achieve the goals of human-machine collaboration and intelligent manufacturing, Jingjiang has adopted a three-step technology development strategy:
1. Security-level monitoring stopped – full coverage of security doors and safety light curtains.
Currently, "Jingjiang" has implemented safety-level monitoring and shutdown functions in all its industrial equipment. This involves complete human-machine separation through safety barriers, and the use of safety doors or light curtains. When an operator's limb enters the machine's working space, a sensor is immediately triggered, and the equipment stops instantly. The equipment resumes operation only after the operator has exited the space and confirmed their presence. This minimizes the risk of production safety accidents.
Waterproof testing equipment for a certain product manufactured by Jingjiang
A barcode scanning device for a certain 3C product manufactured by Jingjiang
Safety railings and safety doors in the Jingjiang testing workshop
2. Trial import of the "Speed and Distance Monitoring" function
After two years of effort, "Jingjiang" has tried to introduce the "speed and distance monitoring" function in situations where close human-machine cooperation is required. The specific implementation method is to use safety light curtains, industrial cameras and distance sensors to sense the distance to workers and to classify the work area. When a worker enters the robot's work area, the robot and all related equipment slow down and switch from normal working mode to "safe mode" so that users can make simple adjustments without stopping the machine. If an unexpected collision occurs, the robot will stop immediately.
3. Human-computer collaboration with direct teaching and collision detection as the ultimate goals
Currently, Jingjiang is increasing its manpower investment in research on zero-force control mode and has achieved certain results in direct torque control technology. In the near future, Jingjiang will embed the "zero-force control with torque mode control" module into all of its small six-axis robots and attempt to add a single-axis torque detection module to certain medium-sized models, in order to reliably realize the "direct teaching" function in the debugging state and the "human-machine collaboration" function in the working state in the near future.
Human-machine collaboration concept (Image from the internet)
Conclusions and Outlook
It must be recognized that we still lag significantly behind world-class levels in human-machine collaboration technology. Our functionalities are incomplete, and due to limited resources, it's difficult to accumulate a vast amount of experience in a short period. Furthermore, our company faces numerous challenges in developing the technologies described in this paper: zero-force control based on position modes requires the use of various types of force sensors, inevitably leading to a significant increase in costs; while direct torque control modes are accompanied by system instability, necessitating a redesign and optimization of safety features.
To address these challenges, we need to invest more in research and development to overcome technical difficulties. We also hope to engage in academic exchanges and collaborations with more research institutes and enterprises to achieve joint breakthroughs. Simultaneously, we hope to see more advanced components in automated tooling equipment, such as more cost-effective force sensors and electronic skin, truly enabling industrial robots and other equipment requiring close human interaction to possess "tactile sensation," and allowing safer, more reliable, and human-friendly equipment to be more widely deployed in industrial production.
