What are the main technical specifications for selecting an industrial robot?

　　For seasoned veterans in the automation industry—experienced mechanical and electrical engineers—choosing the right “robot” may be a straightforward task. However, for designers or factories that are considering purchasing and implementing robots for the first time, the process can feel somewhat daunting.

　　Below, we will discuss how to select an appropriate industrial robot by examining the specifications of nine different types.

　　01 Application Scenarios

　　First and foremost, the critical starting point is to assess the robots being introduced—specifically, the application scenarios they will serve and the types of manufacturing processes involved.

　　When an application requires machines to collaborate alongside human operators, collaborative robots (cobots) are an excellent choice—particularly for typical human–machine hybrid semi‑automatic lines, especially in scenarios where workstations need to be frequently reconfigured or production lines relocated, as well as when paired with advanced torque sensors.

　　If you’re looking for a compact pick-and-place robot, you might want to choose a SCARA robot.

　　In the following discussion, we will focus on multi-axis vertical‑articulated robots. These robots are well suited to a wide range of applications, from pick-and-place operations and palletizing to specialized processes such as painting, deburring, and welding. Today, industrial robot manufacturers typically offer dedicated solutions for virtually every application. All you need to do is specify the task you want the robot to perform and select the most appropriate model from the available options.

　　02 Payload

　　Payload is the maximum load a robot can carry within its workspace, ranging from, for example, 3 kg to 1,300 kg.

　　If you want the robot to pick up a target workpiece and move it from one workstation to another, be sure to account for both the workpiece’s weight and the weight of the robot’s gripper when determining its payload capacity.

　　In addition, it is particularly important to note that the robot’s load curve varies with distance and position within its workspace, resulting in differences in actual payload capacity.

　　03 Degrees of Freedom (Number of Axes)

　　The number of axes in a robot’s configuration directly determines its degrees of freedom. For a straightforward, linear application—such as picking from one conveyor line and placing onto another—a simple four-axis robot is usually sufficient.

　　However, if the application takes place in a confined workspace and the robot arm requires extensive twisting and rotational movements, a 6-axis or 7-axis robot would be the optimal choice.

　　The number of axes typically depends on the specific application. It’s worth noting that, within budgetary constraints, selecting a robot with more axes poses no issue in terms of flexibility. This approach facilitates the reuse and reconfiguration of the robot for other process applications, enabling it to handle a wider range of tasks—rather than running into the problem of insufficient axis count.

　　Robot manufacturers tend to use slightly different naming conventions for their axes or joints. Generally, the first joint (J1) is the one closest to the robot’s base. The subsequent joints are designated J2, J3, J4, and so on, continuing until the wrist end. Meanwhile, other companies, such as Yaskawa/Motoman, use letters to name their robot axes.

　　04 Maximum Operating Range

　　When evaluating the intended application, it’s important to determine the maximum reach required by the robot. Selecting a robot should not be based solely on its payload capacity; the exact reach distance must also be carefully considered. Each manufacturer provides a reach‑area diagram for their robots, which can help assess whether the robot is suitable for a particular application. Pay attention to the robot’s horizontal working envelope, and note the non‑working zones near the base and behind the robot.

　　The robot’s maximum vertical reach is measured as the distance (Y) from the lowest point the robot can access—typically below the base—to the highest point its wrist can attain. The maximum horizontal reach is the distance (X) from the center of the robot’s base to the center of the farthest point its wrist can reach horizontally.

　　05 Repeatability

　　Similarly, this factor also depends on your application. Repeatability can be defined as the robot’s ability to reach the same position each time when performing a routine task.

　　Typically, repeatability ranges from ±0.05 mm to ±0.02 mm, and can even be more precise. For example, if your robot is tasked with assembling an electronic circuit board, you’ll likely need a highly precise robot with exceptional repeatability. Conversely, for coarser operations such as packaging or palletizing, industrial robots do not require the same level of precision.

　　On the other hand, the selection of robotic precision for assembly operations is also linked to the propagation and calculation of dimensions and tolerances across all stages of the assembly process—for example, the positioning accuracy of incoming materials and the repeatability of workpiece positioning within the fixture. This metric is typically expressed in two dimensions as a ± tolerance. In reality, since a robot’s repeatable motion does not follow a linear path but instead occurs in three-dimensional space, the actual position of the robot can lie anywhere within a spherical volume defined by the tolerance radius.

　　Of course, with today’s motion compensation techniques integrated into machine vision systems, the requirements for and reliance on incoming‑part accuracy are reduced, thereby enhancing overall assembly precision.

　　06 Speed

　　This parameter is closely tied to each user. In fact, it depends on the cycle time required to complete the task. The specification sheet lists the robot’s maximum speed, but it’s important to note that, accounting for acceleration and deceleration between points, the actual operating speed will fall somewhere between zero and the maximum speed. This parameter is typically expressed in degrees per second. Some robot manufacturers also specify the robot’s maximum angular acceleration.

　　07 Body Weight

　　The robot’s own weight is a critical factor in designing its control unit. If the industrial robot must be mounted on a custom workstation or even on a rail system, you may need to know its weight to design appropriate support structures.

　　08 Brakes and Moment of Inertia

　　In essence, virtually every robot manufacturer provides information on its robots’ braking systems. Some robots are equipped with brakes on all axes, while others have brakes only on select axes. To ensure precise and repeatable positioning within the work envelope, an adequate number of brakes is essential. In another specific scenario, in the event of an unexpected power loss, the unbraked axes of a loaded robot will not lock, posing a potential safety hazard.

　　Meanwhile, some robot manufacturers also provide the robot’s moment of inertia. In fact, this serves as an additional safeguard for design safety. You may also notice the applicable torque ratings for each axis. For example, if your motion requires a specific amount of torque to perform the task correctly, you should verify that the maximum allowable torque for that axis is sufficient. If the selection is incorrect, the robot could shut down due to overload.

　　09 Protection Rating

　　Select a robot that meets the required Ingress Protection (IP) rating based on its operating environment. Some manufacturers offer product lines of the same robotic arm with different IP ratings to suit various applications. When the robot is used in environments involving food production, pharmaceuticals, medical devices, or flammable and explosive materials, the appropriate IP rating will differ. For example: standard operation—IP40; oil‑mist exposure—IP67; cleanroom ISO class—3.