The types, uses, and user requirements of industrial robots vary, but the main technical parameters to consider include degree of freedom, accuracy, working range, maximum working speed, and carrying capacity.
Degree of freedom
The number of independent coordinate axes that a robot has does not typically include the opening and closing degrees of freedom of its gripper or end effector. In general, it takes 6 degrees of freedom to represent the position and orientation of an object in three dimensions. However, the number of degrees of freedom for industrial robots is designed based on their intended use and can be fewer or more than 6.
For example, the Hitachi-manufactured A4020 assembly robot has 4 degrees of freedom and is capable of connecting electronic components to a printed circuit board. On the other hand, the PUMA562 robot has 6 degrees of freedom and is designed for arc welding on complex, three-dimensional surfaces.
From a kinematic perspective, a robot with additional degrees of freedom beyond what is needed to complete a specific task is referred to as a redundant degree of freedom robot, or simply, a redundant robot. For instance, the PUMA562 robot becomes redundant when performing the task of plugging components onto a printed circuit board.
The use of redundant degrees of freedom increases the robot’s flexibility, helps it avoid obstacles, and improves its dynamic performance. As a comparison, the human arm has a total of 7 degrees of freedom, allowing it to work in a highly versatile and flexible manner, avoiding obstacles, and reaching destinations from various angles.
Industrial robot accuracy is defined by bit accuracy and repeat positioning accuracy. Bit accuracy refers to the difference between the actual and target position of the robot’s hand, represented by the distance between the representative point of repeated positioning tests and the designated position.
Repeat positioning accuracy refers to the robot’s ability to repeatedly position its hand at the same target position, expressed by the degree of dispersion of the actual position value. In practical applications, it is often represented by three times the standard deviation value of repeated test results, indicating the density of error values.
The working range refers to the set of all points that the robot’s arm end or wrist center can reach, also known as the working area. This can vary based on the shape and size of the end effector.
To accurately reflect the robot’s characteristic parameters, the general working range is defined as the working area without the end effector installed. The shape and size of the working range are crucial, as a robot may not be able to complete a task if there is a dead zone that its hand cannot reach.
Maximum working speed
The maximum working speed of industrial robots is sometimes referred to as the maximum stable speed or the composite speed of the arm, and is typically listed in the technical specifications. A higher working speed results in higher work efficiency, but also requires more time for acceleration and deceleration.
Carrying capacity refers to the maximum weight that a robot can handle at any point within its working range. This capacity is determined by not only the weight of the load, but also the speed at which the robot is operating, the magnitude and direction of acceleration, and the quality of the end effector.
For safety reasons, the carrying capacity specification typically refers to the capacity at high speeds. The carrying capacity not only includes the load, but also the quality of the robot’s end effector.