Introduction: what is the degree of freedom, degrees of freedom in various disciplines have different meanings, if it is based on the principle of mechanics, its meaning is that the position of the mechanism can be determined when the number of independent parameters of motion must be given, which is also known as the degree of freedom of the mechanism. This paper focuses on the meaning of the degree of freedom of the robotic arm, as well as the calculation of the degree of freedom of the robotic arm.
Mechanical arm is similar to the human arm, is a kind of multi-degree-of-freedom robot, by a number of drive joints through the mechanical structure of the arm itself is connected one by one, the end of which can realize the spatial multi-degree-of-freedom movement. By installing actuators such as manipulators, suction cups, welding torches, nozzles, etc. at the end, it can replace people to carry out some of the high-intensity, high-risk repetitive work.
Robotic arms usually have six degrees of freedom, generally specialized robotic arms have only two to four degrees of freedom, while most of the general-purpose robotic arms have three to six degrees of freedom. The higher the degree of freedom of a robotic arm, the more complex the action performed by its mechanism. Here is a brief introduction to the meaning of the degrees of freedom of a robotic arm.
Meaning of Degrees of Freedom of a Robotic Arm
The number of joints on a robot arm that can move independently is called the arm's degree of freedom of movement. The control method adopted by industrial robots is to treat each joint on the robotic arm as a separate servo mechanism, and each axis corresponds to a servo, and each servo is controlled through a bus, which is controlled and coordinated by the controller in a unified manner.
Six degrees of freedom are generally used in the design of industrial robots, which are translation along the x-axis, y-axis, and z-axis; rotation around the x-axis, y-axis, and z-axis. The first three degrees of freedom are used for determining the position, and the last three degrees of freedom are used for determining the attitude in order to realize the control of the robot arm. One reference plane coincides with the bottom surface of the object, limiting the object to translate along the z-axis, rotate around the x-axis, and rotate around the y-axis with three degrees of freedom; two reference planes coincide with the back side of the object again, limiting the object to translate along the x-axis and rotate around the z-axis with two degrees of freedom; three reference planes coincide with the other side of the object, limiting the object to translate along the y-axis with one degree of freedom.
If according to the different structural form of the robot arm can be divided into horizontal multi-joint robot arm and Cartesian coordinate system robot arm and so on. Horizontal multi-joint robotic arms generally have three main degrees of freedom: Z1-axis rotation, Z2-axis rotation, and Z-axis translation, and by adding X-axis rotation and Y-axis rotation to the end of the actuator, it can reach any coordinate point in the space. Cartesian coordinate system robotic arm generally consists of three main degrees of freedom, X-axis translation, Y-axis translation, Z-axis translation, by adding X-axis rotation, Y-axis rotation and Z-axis rotation at the end of the actuator, it can reach any coordinate point in the space.
Calculation of Degrees of Freedom of Robotic Arm
Calculation of the degrees of freedom of the robotic arm is a prerequisite in the design of the robotic arm. By calculating the degrees of freedom of the robotic arm, it is possible to know the type of motion that may be generated by the robotic arm, e.g., if the joints of the robotic arm need to be moved only up and down, it is necessary to restrict the joints to rotate around the X-axis, the Y-axis, the Z-axis, and to move along the direction of the X-axis and the Y-axis. The degrees of freedom of a robotic arm can be categorized into planar and spatial degrees of freedom, and their degrees of freedom can be calculated using simple calculations.
The planar degrees of freedom are calculated. If all the joints of the arm are k, minus the fixed member (the seat), the number of joints of the arm in motion is n=k-1. Before the joints are connected by the motion subs, the total number of degrees of freedom of these joints is 3n. When the motion subs connect these joints to form the arm, the number of degrees of freedom of the individual joints of the arm decreases, and the total number of constraints introduced by all the motion subs in the arm is 2PL+PH. Therefore, the total number of degrees of freedom of the joints less the total number of constraints introduced by the motion subs is equal to the degrees of freedom of the arm. The total number of constraints introduced by all the motion subs in the arm is 2PL+PH. So, the total number of degrees of freedom of the joints minus the total number of constraints introduced by the motion subs is equal to the degree of freedom of the arm, i.e., F=3n-2PL-PH is the way of calculating the planar degrees of freedom.
The way to calculate the spatial degrees of freedom. First of all, we need to know that the robotic arm has six degrees of freedom in space, unlike the three degrees of freedom it has in the plane. Their calculation is basically the same, are the total number of degrees of freedom of the joints minus the total number of constraints introduced by the motion vice is equal to the degree of freedom of the robotic arm, the calculation: F = 6n-5P5-4P4-3P3-2P2-P1. F represents the degree of freedom of the robotic arm, 6n represents the total number of degrees of freedom of the joints, and P1, P2, P3, P4, and P5 represent the number of 1-5 levels of the motion vice, respectively.
Browse the above article to understand the meaning of the degree of freedom of the robotic arm and how to calculate, the number of joints on the robotic arm that can move independently is the degree of freedom of the robotic arm. The number of joints on the arm that can move independently is the number of degrees of freedom of the arm. Usually when designing a robotic arm, we will use the calculation of its degrees of freedom to know the possible movement of the arm through the calculation. Follow us to learn more about the degrees of freedom of robotic arms and their applications.