For seasoned professionals in the automation industry, experienced mechanical and electrical engineers, choosing the right robot might be a simple task. However, for designers or factories preparing to purchase and implement robots for the first time, it can be quite disconcerting.
The following discussion covers nine key parameters to determine how to select a suitable industrial robot .
01 Application Scenarios
First and foremost, the most important starting point is to evaluate the robots being introduced, determining their intended application and manufacturing process.
If the application process requires machines to work alongside humans, especially in the case of semi-automatic lines with human-machine interaction, particularly in situations where frequent changes in workstations or line shifts are needed, and in conjunction with new torque sensors, collaborative robots (Cobots) should be a good option.
If you are looking for a compact pick and place robot, you might want to choose a horizontal articulated robot (Scara).
If you're looking for a solution that allows for quick handling of small objects, the Delta parallel robot is the best fit for that need.
The following discussion will focus on multi-axis vertical joint robots. These robots can be adapted to a very wide range of applications, from picking and placing materials to palletizing, as well as specialized processes such as painting, deburring, and welding. Currently, industrial robot manufacturers basically have robot solutions for every application process. All you need to do is clearly define which task you want the robot to perform and select the most suitable model from the different types available.
02 Payload
Payload is the maximum load a robot can carry within its workspace. It can range from, for example, 3 kg to 1300 kg.
If you want the robot to move a target workpiece from one station to another, you need to add the weight of the workpiece and the weight of the robot's gripper together to its workload.
Another important point to note is the robot's load curve, as its actual load capacity will vary at different distances within the spatial range.
03 Degrees of freedom (number of axes)
The number of axes a robot has is directly related to its degrees of freedom. For a simple, straightforward task, such as picking up and putting items from one conveyor belt to another, a simple 4-axis robot is sufficient.
However, if the application scenario is in a small workspace and the robotic arm needs a lot of twisting and turning, a 6-axis or 7-axis robot will be the best choice.
The number of axes generally depends on the application. It's important to note that, within cost limits, selecting a higher number of axes is not necessarily a problem in terms of flexibility. This facilitates the subsequent reuse and modification of the robot for another application process, allowing it to adapt to more tasks, rather than discovering that the number of axes is insufficient.
Robot manufacturers tend to use slightly different names for their axes or joints. Basically, the first joint (J1) is the one closest to the robot's base. The next joints are called J2, J3, J4, and so on, until reaching the end of the wrist. Other companies, like Yaskawa/Motoman, use letters to name the axes of their robots.
04 Maximum range of motion
When evaluating a target application, it's essential to understand the maximum distance the robot needs to reach. Choosing a robot isn't solely based on its payload—the exact distance it can reach must also be considered. Each company provides a range of motion diagram for their robots, which helps determine if the robot is suitable for a specific application. The diagram shows the robot's horizontal range of motion, paying attention to the non-working area near and behind the robot.
The robot's maximum vertical height is measured as the distance (Y) from the lowest point the robot can reach (usually below the robot's base) to the maximum height the wrist can reach. The maximum horizontal actuation distance is the distance (X) from the center of the robot's base to the center of the furthest point the wrist can reach horizontally.
05 Repeatability
Similarly, this factor still depends on your application. Repeatability can be described as the robot's ability to reach the same position every time it completes a routine task.
The precision is typically between ±0.05mm and ±0.02mm, or even higher. For example, if your robot needs to assemble an electronic circuit board, you might need a robot with extremely high precision and repeatability. If the application process is relatively rough, such as packaging or palletizing, the industrial robot does not need to be so precise.
On the other hand, the selection requirements for robot precision in assembly processes are also related to the transfer and calculation of dimensions and tolerances in various stages of the assembly process, such as the positioning accuracy of incoming materials and the repeatability of the workpiece itself in the fixture. This indicator is represented by ± in 2D. In fact, since the robot's motion repetition points are not linear but move in 3D space, this parameter can actually be located at any position within a spherical space within the tolerance radius.
Of course, with the motion compensation technology of current machine vision, the requirements and reliance of robots on the accuracy of incoming materials will be reduced, and the overall assembly accuracy will be improved.
06 Speed
This parameter is crucial for every user. In fact, it depends on the cycle time required to complete the task. The specifications list the maximum speed of the robot model, but we should know that considering acceleration and deceleration from one point to another, the actual operating speed will be between 0 and the maximum speed. This parameter is usually measured in degrees per second. Some robot manufacturers also specify the robot's maximum acceleration.
07 Body weight
The weight of the robot itself is an important factor when designing a robot unit. If an industrial robot must be mounted on a custom-made machine tool, or even on a guide rail, you may need to know its weight to design the appropriate support.
08 Braking and Moment of Inertia
Basically, every robot manufacturer provides information on their robot's braking system. Some robots are equipped with brakes on all axes, while other robot models do not. A sufficient number of brakes are needed to ensure accurate and repeatable positioning within the work area. Another special case is the risk of accidents occurring in the event of a power outage; without brakes, the axes of a heavy-duty robot may not lock, posing a potential safety hazard.
Additionally, some robot manufacturers also provide the robot's moment of inertia. This provides an extra layer of safety for the design. You might also notice the applicable torque on different axes. For example, if your motion requires a certain amount of torque to complete the task correctly, you need to check if the maximum torque applicable to that axis is correct. Incorrect selection could cause the robot to crash due to overload.
09 Protection Level
Depending on the robot's operating environment, a standard meeting a certain protection level (IP rating) should be selected. Some manufacturers offer product lines with the same robotic arm but different IP protection levels for different applications. The IP rating will differ if the robot is operating in environments involving the production of food-related products, pharmaceuticals, medical devices, or flammable and explosive materials. Generally, for example, standard: IP40, oil mist: IP67, cleanliness ISO rating: 3.
