What should I do if the temperature is too low and the robot cannot start?

As a widely used equipment at home and abroad, it is widely used in spot welding, handling, gluing, arc welding and roller edge processes in the automotive manufacturing industry. As a complex integrated system, due to other related constraints, the industry has experienced a transformation from difficult to flexible application. In view of these application situations, the problems and solutions of robots in low temperature environment conditions are discussed.

Every winter, field operations are always affected by bad weather. I believe that in this season, everyone has encountered the problem that the temperature is too low and the robot cannot be started. In addition to those conventional heating methods to make the robot "alive", is there any treatment method that is in line with the temperament of our high-end smart devices?

Problems

The ambient temperature is -10 to 40°C. At present, the industrial robots in the welding workshop are in the production stage. When the ambient temperature is low in early winter (the air conditioner in the workshop is not turned on, and the ambient temperature is lower than 10°C), some industrial robots may collide with external equipment, deviate from the robot's running trajectory, have excessive joint loads, or have an axis overload during welding, handling, and rolling . After the robot returns to its original position manually, the automatic running speed of the robot is reduced and production is resumed, and the robot failure disappears.

Next, we will use theory and practical experience to tell you how to deal with the above problems!

//1. ABB Robot

In the early winter of the welding workshop, especially during the morning production line startup, the ABB robot frequently had "joint load too high" and "motion monitoring" alarms. The actual torque of the robot joint ROB_X (as shown in Figure 1, X represents the robot joint axis, ROB1_2 is the second joint axis of robot 1) was too high, which may be due to load data errors, excessive acceleration, excessive external process force, low temperature or failure. After the technicians confirmed the status on site, the robot did not collide with objects such as equipment and workpieces, and ruled out excessive torque or load caused by jamming and collision. The robot motion monitoring was triggered and the movement of the robot unit was immediately interrupted.

//2. KUKA robot

Also in the early winter, the air conditioner was not turned on and the ambient temperature was below 10°C. Especially in the morning when the line was turned on, the KUKA robot frequently reported "exceeding the maximum hysteresis error (X)" (as shown in Figure 2, X is the robot or the auxiliary mechanical joint axis, KSP is KUKA SERVO PACK, and 1 is the servo control of the first axis).

KUKA robot alarm interface //3. FANUC robot

Japanese robots are mostly lubricated with grease. When the temperature is low or the robot is shut down for a long time, the grease is prone to solidification and the resistance increases. When the resistance increases, it will trigger a collision.

FANUC robot alarm

Problem analysis and solution:

//1. Unsmooth robot motion trajectory

The robot's running trajectory on site is mainly generated by manual teaching. The trajectories in the teaching process are different, and the generated trajectories are not necessarily smooth. During the operation of the robot, if the movement of a certain axis at certain positions is relatively large, and the speed and acceleration are very large, a momentary overcurrent will occur in the axis.

This is due to improper setting of the position and motion parameters of a certain trajectory point in the program . You can observe the position where the alarm is generated each time to see if it is at the same position. If so, optimize the position of the point appropriately and reduce the speed and acceleration of the point appropriately.

// 2. Check the hardware

If the problem continues to occur on site, that is, it occurs frequently, you need to check the hardware, including motors, cables, servo drives and other related hardware, and replace the corresponding modules. It should be noted that only the corresponding part of the alarm axis needs to be replaced.

This article refers to ABB robots and KUKA robots, and specifically points out that the KPP/KSP of the KUKA robot cannot be replaced at the same time, otherwise an error will be reported and they must be replaced one by one.

// 3. Temperature reasons

Working in a low temperature environment will cause the viscosity of the grease inside the robot to be high . When the robot starts running, the high viscosity of the grease will cause greater resistance to the operation of the equipment, resulting in increased friction in the gearbox, and thus requiring a larger motor torque to overcome the resistance. For this reason, the motor current of one axis (or multiple axes) will reach the maximum value. At the same time, when the temperature is low, the robot's circuit board will also be affected, because the circuit board is mainly made of materials, and semiconductors are unstable in low temperature environments, which may cause problems such as the robot control system freezing or the robot taking a long time to start.

The temperature characteristics of ABB industrial robots are stored at a temperature of -25 to 55°C. The maximum temperature that can be tolerated when the storage time is less than 24 hours is 70°C, and the maximum humidity that the robot can withstand at room temperature is 95%. The operating temperature range of the robot is 5 to 50°C, and the maximum humidity that the robot IRC5 can withstand at room temperature is 95%.

The storage temperature of robot IRC5 is -25～55℃, the maximum temperature it can withstand in storage is 70℃, and the maximum humidity that the robot can withstand at room temperature is 95%. The operating temperature of IRC5 is 5～45℃, and the maximum humidity that robot IRC5 can withstand at room temperature is 95%.

The storage temperature of the KUKA industrial robot is -40 to 60°C, and the operating temperature of the robot is 10 to 55°C. The storage temperature of the robot KRC4 is 5 to 45°C.

// 4.Solution ​

The solution we came up with for robot gear grease is to add antifreeze to the grease in a low-temperature environment. The components of robot grease are additives and grease (grease is generally synthetic oil), but it is generally monopolized by manufacturers and the composition is confidential. ABB robot grease is Japan Kyodo Oil and Mobil grease, and KUKA robot grease is a certain type of Castrol oil.

Since the composition of the grease is confidential, it is not recommended to add any additives without consulting the manufacturer or professionals, because the addition of any ingredients will affect the characteristics of the overall gear grease and may damage the gears of the robot shaft and the seals of the gearbox, etc.

For more questions about grease, you can consult more professional Zhinan Car! Zhinan Car's special lubricating oil is more resistant to high and low temperatures.

In addition to the above methods, ABB robots, KUKA robots and other robots can run at a low speed for a period of time at the beginning of production, and gradually increase the speed to restore to the robot's external full speed or the beat required by the customer. The motor current of the KUKA robot can be monitored through the preheating function. Once the set value is reached, the control system will automatically reduce the movement speed, thereby reducing the motor current.

FANUC robot has reserved di speed selection

Menu-Settings-di speed selection-Enable, configure io, set the required speed.

The application of industrial robots is to cooperate with the production process and improve the level of automation. We need to pay enough attention to the management and troubleshooting of robots in the early stage of equipment installation and commissioning. I hope this article can provide reference help for the problem of industrial robot shaft overcurrent.

Editor: Huang Fei