Abstract: With the development of robotics, robots are divided into general robots and intelligent robots according to their functions. Among them, general robots refer to robots that only have general programming and operating capabilities. At present, most of the robots produced in China belong to this category. The original industrial robots can only move or move in a fairly closed space, with extremely limited safety functions. The safety performance is not high. With the subsequent emergence of automation control theory and safety devices, the safety functions are gradually improved, making industrial robots able to adapt to more production environments and work tasks, and also making it possible for man-machine coordination to work, but safety accidents It still happens from time to time. As countries in the world pay more and more attention to the safety of people’s lives and property, how to ensure the safe and reliable operation of industrial robots has become more and more important.
1 Risk assessment of industrial robots
Regarding the dangerous factors of machinery and equipment, relevant international and domestic standards have proposed a set of systematic procedures, with the purpose of selecting and adopting appropriate safety measures to reduce or eliminate risks.
1.1 Hazard identification of industrial robots
In order to prevent or reduce the injuries caused by robots, it is necessary to identify the common hazards that occur in the robot post, so that the dangers can be easily identified and analyzed during the design and risk assessment of the robot and its system. For industrial robots and their systems, their hazards are not the same. Common hazards mainly include: facility failure or malfunction, mechanical component movement, energy storage or power source, dangerous gases, materials or conditions, hazards caused by noise, interference The dangers caused by human errors (including design, manufacturing, installation, trial operation, testing, programming, verification, maintenance, etc.), the movement, handling or replacement of robot systems or auxiliary components, etc.
1.2 Risk assessment of industrial robots
Risk is related to special circumstances or the hazard considered in the process of technological development. It is a function of the severity of the hazard's possible harm, the probability of occurrence of the injury, and the possibility of avoiding or limiting the injury.
In order to support the robot risk assessment process, there are many effective risk assessment tools, and users can use different assessment tools according to different robots. Industrial robots generally recommend the use of numerical scoring methods. A specific value represents the acceptable risk level, which can provide a key basis for risk reduction.
2 Safety design of robot control system
The control system is the core of the robot, and ensuring the normal and stable operation of the control system is the key to the realization of safety functions. However, the performance and stability of the control system are often mutually restricted. If the control work of the robot is to be completed better and safer , There must be a balance between the two. From the perspective of safety control, the robot control system design should meet the following points:
(1) Adopt a sophisticated, mature, stable and standardized software development platform to meet the configuration and software programming of safety function related parameters.
(2) Development-type control system, safety modules and safety devices can be added freely, with scalability and interoperability.
(3) The real-time performance is good, and the peripheral security-related tasks can be processed in time. High reliability is one of the primary problems to be solved in the control technology of complex robots. Only by solving the reliability of the control system can the uncertain factors brought by the development of industrial robot technology be solved. P21, the existing new Shida robot control system software development platform adopts It is the CODESYS multi-axis robot control system of Germany 3S company. Its development is smart and real-time, which can meet the reliability requirements of the safety function of the robot control system development.
3 The realization strategy of the safe stop function of the robot in different states
When an external signal triggers or an abnormal state occurs, the robot should be stopped in an appropriate manner. The braking method to be used is mainly determined from the perspective of risk analysis and comprehensively considering factors such as robot safety and performance.
3.1 When the servo drive power supply is disconnected
According to the electrical schematic diagram of the above safety circuit, there are several possibilities for the power supply disconnection of the servo drive:
(1) The external power supply is disconnected, such as a sudden power failure in the factory.
(2) The contactor coil is disconnected, the main reason may be contactor failure, safety circuit failure, etc. At this time, if the robot servo system is in the enabled or running state, after the control system detects the main power disconnect signal, according to the general processing procedure, the servo should immediately turn off the motor holding room and then turn off the servo enable output, which is equivalent to triggering The emergency braking process, but due to the delay of the motor holding the Min itself, a certain degree of falling problems will inevitably be brought about according to factors such as the current position, attitude and speed of the robot.
First of all, when the servo drive is powered off, the robot servo system is in the enabled state and the motor is in the enabled state (the speed is close to zero).
(1) At this time, the possible source of danger is mainly from the fall or fall of the mechanical parts. The root cause is that the braking delay time of the braking device (motor drag room) is not enough to respond to the impact of the gravity fall of the mechanical parts. According to the analysis of the risk assessment The process, severity, probability of occurrence of injury, and possibility of avoidance belong to S1 (mild injury), E1 (infrequent exposure), A1 (may be avoided), generally simple safety control and training awareness can be used avoid.
3.2 When the robot control system is controllable and alarms
When the robot control system reports to the general public, the robot immediately brakes and stops. Which brake stop method is used depends on the type of report. From the perspective of the servo system, it is mainly divided into controllable alarms and uncontrollable alarms. The difference between them is as follows:
(1) Controllable report glimpse, the servo system enable output is not turned off when the alarm, the motor is controllable, and the severity is relatively low alarm, such as input phase loss, position overrun, smart fault, etc.
(2) Uncontrollable alarm, when the servo system enables the output to be turned off immediately, the motor is uncontrollable, and alarms with higher severity, such as motor overcurrent, encoder failure, servo overload, etc.
4.3 When the robot servo system is uncontrollable and alert
At this time, the possible hazards mainly come from the high-speed movement of mechanical components and the possible fall after braking. According to the analysis process of risk assessment, the severity, the probability of injury, and the possibility of avoiding belong to S2 (serious damage ), E2 (infrequent exposure), A1 (may be avoided), generally need to adopt reliable safety control and safety fence to avoid, but the probability of occurrence of injury is relatively low, the following further analysis how to reduce this risk.
(2) If there is no dynamic braking process, the motor will not stop quickly, and a certain drop will occur when the load and speed are large, and only emergency braking will increase the wear of the motor and affect its service life.
(3) Same as the controllable alarm, the main power supply needs to be disconnected by the safety circuit.
5 Test method for safety function of robot system
The common method of functional testing is black box testing, that is, the system function is regarded as a black box that cannot be opened, and the system function interface is tested without considering the internal structure and internal characteristics of the system. The robot function test only needs to check whether the system function is used normally according to the function requirements, whether the control system can properly receive the input signal and perform the correct action. The black box test is more often from the user's perspective, from the input data The corresponding relationship with the output result is tested. Obviously, if there is a problem with the design of the control system itself, it will not be discovered by the black box test method.
The general steps of the robot system function test: first prepare the relevant documents, understand the requirements, and fully and accurately understand the functions to be realized by the robot system, understand the actual operation steps and environmental conditions, and then proceed to formulate the test test cases.
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