Joint / Linear Movement

There are two primary ways to move the robot from one waypoint to another, by going in a straight line through either the joint space or the task space. As we saw, two points in space can be both described by their joint space coordinates (the set of joint angles to position the robot at the waypoint), or their task space coordinates, the cartesian coordinates representing the translation and rotation of the tool. Going in a straight line from one point to another in joint space means that the robot controller will only look at the joint angle of both waypoints and linearly interpolate from one to another. In practice this would mean that if joint 1 must start at 0 degrees, and finish at 30 degrees, the controller will smoothly move the joint between the 2 values, resulting in a curved trajectory of the tool in task space. On the other hand, going in straight line in task space, means that the robot controller will only look at the waypoints' cartesian coordinates and smoothly interpolate between the two, resulting in a straight line for the tool, but a curved trajectory in joint space (some joints might move very slowly or rapidly in an unpredictable manner). A Joint movement will then be specified with a speed in degrees/sec for the maximum rotation of each joint, while a Linear movement will be specified as a cartesian speed in mm/sec of the tool in space. Projects that do not focus much on the tool but on large movements of the robot in space will often want to use Joint movements, while projects requiring precise positioning of the tool will want to use Linear movements. It is also very common to mix both during sequences alternating with a focus on the tool or on the whole robot.