Robots are programmed using "on-line" or "off-line" methods.
On-Line Programming For basic Robot tasks such as paint spraying and simple pick and place the Robot programming method
is on-line. This means that the Robot moves in sympathy with commands used by the
teacher / programmer. On line programming a record play-back approach where the
Robot plays back a sequence of moves. There are two types of on-line teaching:-
1) Lead-Through This method is used to teach Robots to carry out such tasks
as paint spraying or Applying adhesive to an irregular surface. The Robot arms using
this teaching method are typically ones with wrist motion plus three degrees of
freedom and having revolute joints. The Robot is taken through its operating cycle
manually and the movements of each axis are logged automatically at frequent
intervals. The joint position sensors ( potentiometer or encoded discs ) provide
position information as the Robot is moved through its cycle. The positional
information is sampled periodically and stored in the computer memory. When played
back the end effector appears to follow a continuous path.
Moving the limbs of an undriven Robot can impair the free hand movements of the
teacher, in order to overcome this problem the programming can be done using a
skeleton arm or counter balanced arm just for the teaching process.
This method has the advantage of simplicity but requires reprogramming for each new
task eg. painting a different component.
2) Drive-Through This programming method is used for industrial tasks of a
pick and place nature such as spot welding and machine loading and unloading.
The Robot movements are controlled by inputs from a teach pendant or keypad, the
programmer can specify the movement and velocity of each robot limb between two
points. The Robot cycle is a sequence of such movements which can be observed
during the programming. In the play-back period the programmer can modify the
sequence to get optimum cycle time and accuracy.
The majority of Robots on the marlcet use drive through programming. The
programmer need not be skilled in the Robot task as in the case of lead through. When
programming the operator may need to be very close to the driven robot, this can
create potential safety problems.
A typical Teach Pendant
Off-line programming of Robots is used to control the overall sequence of
tasks carried out in a Robot serviced system. The drive through programming method
will still be used but only at discrete points in the overall sequence where positional
accuracy is required. In off line programming the program uses a high level computer
language such as VAL which gives the Robot decision making power. This method
needs a large amount of computing power and incorporates the use of sensors on the
Robot or within its environment to provide system status information. Typical input
sensos could be of the position, vision and tactile types. Information from the sensors
can allow the Robot to take alternative action within its overall task cycle. eg A Robot
being fed by a number of machines will only stack finished components from a machine
where a component is available. Using off line programming the Robot can make
decisions such as counting a number of operations or perform one task until another is
ready to be started. Robots which are off-line programmable are more useful in a
production situation since they can be reprogrammed with a minimum of interference
to the production process.
(a) Off-line programming
(b) Coordinate entry programming