ve historically been taught .e. using the robot’s ‘teach o manually drive the robot’s desired point along the part ated on, while visually as much as feasible – the ccuracy. iously a time-consuming o be painstakingly repeated elevant) point along the h in space; furthermore, this early doesn’t provide a high sitional accuracy.
Robot Simulation software, commercialized nowadays by various companies, offers the ability to model an entire robot-cell on computer prior to dealing with it on the actual plant floor: a desired robot model is chosen, the end-effector and the fixture can be modeled, the part can be imported from some other CAD software – all that allowing the final robot program (with all required speeds and including any other desired commands) to be entirely created upfront through Simulation. The created robot program is – theoretically – ready to be executed on the actual robot: this process is referred to as Off-Line Programming (OLP). More specifically, ‘Downloading’ is the process of transferring robot programs created through Simulation software in a ‘nominal’ environment, to the ‘actual’ robot-cell on the plant floor;
In reality, the differences between the ‘nominal’ world in Simulation and the ‘actual’ environment on the plant floor prevent from directly executing on the robot controller a robot program created through Simulation: each robot unit is built with certain manufacturing tolerances; the end-effector and its TCP deviate from their design intent; the fixture holding the part is not located relative to the robot coordinate frame as desired; etc. As a result, the robot programs downloaded from Simulation will not follow the intended path on the plant floor. This doesn’t just affect the positioning of the robot’s TCP, but it can also cause collisions between the robot and other peripherals within the robot-cell.
A robot program generated through Off-Line Programming is accurate enough if the resulting positioning accuracy of the robot’s TCP is within the acceptable limits for the intended application. For example, Off-Line Programming resulting in good enough robot programs for a paint job might not be so for an engine component assembly application. To maximize the success of Off-Line Programming (minimum manual robot program touchup and collision avoidance), it is generally imperative to perform ‘Robot-Cell Calibration’, and to correct accordingly (i.e. ‘Filter’) the robot programs to be downloaded.
A robot is generally capable of repeating the same move towards a specific point in space, over and over, within a high level of tolerance (referred to as ‘unidirectional Repeatability’), generally well below 0.1mm. But this does not mean that that particular point in space is well known relative some global coordinate frame (such as the robot base frame):
The level of ‘Absolute Accuracy’ achieved by an ‘off-the-shelf’ industrial robot is generally in the several millimeters and more. This is generally due to manufacturing tolerances for every robot unit, incorrect joint zero-mastering, mechanical flexibility, gear backlash, etc.
