Joint and Linear Motion
Motion control affects how a job is completed by an industrial robot. There are two main types of motion that are used with industrial robots: joint motion and linear motion.
For some applications, a robot needs merely return repeatedly to a limited number of programmed positions. This type of motion is called joint motion. Joint motion, also known as Point-to-Point motion, only uses start and stop locations. The path is predictable, however it will not be linear. Joint motion is often faster and is used for tasks, like picking up and placing disks, when the path does not need to be precise.
With linear motion, the path is very important. Linear motion is typically used when motion must be continuously controlled to follow a path in space with precision and accuracy. With the VEX V5 Workcell, linear motion is important for drawing shapes or other tasks with a need for precision while following a path. Linear motion takes more time and is used for more sophisticated applications, such as welding, cutting, finishing, or painting.
Robot Dynamics
As a robot’s arm moves there are many forces acting on it. There are outside forces such as friction, gravity acting on the arm, and gravity acting on the payload/tool. Then there are the forces coming from the robot’s actuators to overcome the outside forces. Collectively, these forces define a robot’s dynamics, in other words, how it moves.
If the forces are balanced the robot is in a steady state, meaning the robot arm is not moving or it is moving in a constant velocity (speed and direction). If the forces are not balanced, then the robot arm will be changing its motion. For instance, if the arm mounted on the V5 Workcell is programmed to move to a specific x, y, and z coordinate, there will be a number of robot dynamics which will come into play.
The joints on the arm mounted on the V5 Workcell all need to provide a coordinated set of forces which are greater than the forces of friction and gravity acting on the V5 Workcell to create the unbalanced forces to move to its new location. Once the arm mounted on the V5 Workcell reaches the new set of coordinates, the arm’s motors need to provide a balanced set of forces equal to the gravity forces acting on the arm to keep it at its new location.
It should be evident that, whether it be the robot’s controller and operating system or a robot’s dynamics, there are many factors which need to be considered when programming a robotic arm to move and complete a task.