In the application of industrial robots, the robot body is usually selected to meet the usage conditions, while the end effector is customized for different industries and environments.
The main selection principles for robot bodies are: payload, application industry, maximum range of motion, operating speed, braking and rotational inertia, protection level, degrees of freedom, body weight, and repeatability accuracy.
1. 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.
2. Industrial robot application industries
Where you intend to use your robot is the primary factor when choosing the type of robot you need to purchase. If you simply need a compact pick-and-place robot, the SCRA robot is a good choice. If you want to quickly place small items, the Delta robot is the best option. If you want robots to work alongside workers, you should choose collaborative robots.
3. 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.
4. Operating 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.
5. 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.
6. Protection level
This also depends on the required protection level for the robot's application. The required protection level varies depending on whether the robot works with food-related products, laboratory instruments, medical equipment, or is in a flammable environment. This is an international standard, and the required protection level needs to be differentiated based on the specific application or local regulations. Some manufacturers offer different protection levels for the same model of robot depending on the operating environment.
7. Degrees of freedom (number of axes)
The number of axes a robot has determines its degrees of freedom. For simple applications, such as picking and placing parts between conveyor belts, a 4-axis robot is sufficient. If the robot needs to work in a confined space and the robotic arm needs to twist and turn, a 6- or 7-axis robot is the best choice. The choice of the number of axes usually depends on the specific application. It's important to note that having more axes doesn't just mean more flexibility. In fact, if you plan to use the robot for other applications, you might need even more axes—you'll regret not having enough when you need them. However, having more axes also has disadvantages. If you only need 4 of the 6-axis robots, you still need to program the remaining 2 axes.
8. Robot body weight
Robot weight is also an important parameter for designing robot cells. If an industrial robot needs to be mounted on a custom workbench or even a track, you need to know its weight and design the appropriate support.
9. Repeatability
The choice of this parameter also depends on the application. Repeatability is the accuracy/variability with which the robot reaches the same position after each cycle. Typically, robots can achieve accuracy within 0.5mm, or even higher. For example, if the robot is used to manufacture circuit boards, you will need a robot with extremely high repeatability. If the application does not require high precision, then the robot's repeatability does not need to be as high. Accuracy is usually represented by "±" in 2D views. In reality, since robots are not linear, they can be located anywhere within the tolerance radius.
