In lead through programming, the robot is moved through the desired motion path in order to record the path into the controller memory.
There are two ways of accomplishing lead through programming:
- Powered lead through
- Manual lead through
The powered lead through method makes use of a teach pendant to control the various joint motors, and to power drive the robot arm and wrist through a series of points in space.
Each point is recorded into memory for subsequent play back during the work cycle. The teach pendant is usually a small handheld control box with combinations of toggle switches, dials, and buttons to regulate the robot’s physical movements and programming capabilities.
Among the various robot programming methods, the powered lead through method is probably the most common today.
It is largely limited to point-to-point motions rather than continuous movement because of the difficulty in using the teach pendant to regulate complex geometric motions in space.
A large number of industrial robot applications consist of point-to-point movements of the manipulator. These include part transfer tasks, machine loading and unloading, and spot welding.
The manual lead through method (also sometimes called the ‘walkthrough’ method) is more readily used for continuous-path programming where the motion cycle involves smooth complex curvilinear movements of the robot arm.
The most common example of this kind of robot application is spray painting, in which the robot’s wrist, with the spray painting gun attached as the end effector, must execute a smooth, regular motion pattern in order to apply the paint evenly over the entire surface to be coated.
Continuous arc welding is another example in which continuous path programming is required and this is sometimes accomplished with the manual lead through method.
In the manual lead through method, the programmer physically grasps the robot arm (and end effector) and manually moves it through the desired motion cycle.
If the robot is large and awkward to physically move, a special programming apparatus is often substituted for the actual robot.
This apparatus has basically the same geometry as the robot, but it is easier to manipulate during programming.
A teach button is often located near the wrist of the robot (or the special programming apparatus) which is depressed during those movements of the manipulator that will become part of the programmed cycle.
This allows the programmer the ability to make extraneous moves of the arm without their being included in the final program.
The motion cycle is divided into hundreds or even thousands of individual closely spaced points along the path and these points are recorded into the controller memory.
The control systems for both lead through procedures operate in either of two modes: teach mode or run mode.
The teach mode is used to program the robot and the run mode is used to execute the program.
The two lead through methods are relatively simple procedures that have been developed and enhanced over the last 20 years to teach robots to perform simple, repetitive operations in factory environments.
The skill requirements of the programmers are relatively modest and these procedures can be readily applied in the plant.