Robot Programming

The greatest force of robots is their flexibility, their ability to rearrange for new production and their large movement range. Utilization of the robot's flexibility presupposes effective programming. The robot programming can take place in two principally different ways: on-line or off-line. In On-line programming the use of the robot and equipment is required, whereas off-line programming is based on computer models of the production equipment. Both these methods have advantages and disadvantages. In this section we will take a look at how the two methods can be combined.

On-line programming

On-line programming takes place at the site of production itself and involves the workcell. The robot is programmed with a teach box. On-line programming has the following advantages and disadvantages compared to off-line programming:

Advantages Easily accessible.

Disadvantages Slow movement of the robot while programming. Program logic and calculations are hard to program. Suspension of production while programming. Cost equivalent to production value. Poorly documented.

The most significant advantage of on-line programming is that the robot is programmed in concordance with the actual position of equipment and pieces. Contrary, the most significant disadvantage is that it occupies valuable production equipment.

Off-line programming

Off-line programming takes place on a computer and models of the workcell with robot, pieces and surroundings are used. The robot programs can in most cases be created by the reuse of existing CAD data so that the programming will be quick and effective. The robot programs are verified in simulation and any errors are corrected.

Off-line programmering in Ropsim.

Advantages Effective programming of program logics and calculations with state-of-the -art debugging facilities. Locations are built according to models and this can mean that programmers will have to fine tune programs on-line or utilize sensors. Effective programming of locations. Verification of program through simulation and visualization. Well documented through simulation model with appropriate programs. Reuse of existing CAD data. Cost independent of production. Production can continue while programming. Process support tools for instance selection of welding parameters.

Disadvantages Demands investing in an off-line programming system.

The biggest advantage of Off-line programming is that it does not occupy production equipment, and in this manner production can continue during the programming process. By far the largest proportion of robots are today being programmed on-line. This is mainly due to the fact that off-line programming has had a very high burden rate and demanded the need of expert users.

Advanced off-line programming tools contain facilities for debugging and these assist effective programming. The programming tools support utilization of supporting tools for the programming process, for instance optimization of the welding process.

The robot off-line programming and simulation system Ropsim takes costs to an attractive level and runs under Microsoft Windows with well-known present-day user interface.

Hybrid programming

By utilizing the advantages of both of these methods the programming technique can be optimized. This is generally referred to as hybrid programming. A robot program consists mainly of two parts: locations (position and alignment) and program logics (controller structures, communication, calculations).

The program logics can effectively be developed off-line as effective debugging and simulation facilities are available here. The major part of movement commands can be created off-line by the reuse of CAD data and by interaction of the programmer.

Movement commands to locating the placement of the piece in the robot's workcell can be programmed on-line if need be. In this manner both method's advantages can be utilized. By using both of these programming methods an increased flexibility can be achieved in production.

If we let the constructor off-line program the robot's working of the piece the constructor's knowledge of the product properties can be utilized. Often, however, the constructor has no knowledge to the actual placement of the piece in the production cell.

If we let the robot operator on-line program the precise placement of the piece a faster rearrangement is achieved. The on-line programmed points are used for adjusting the program that the constructor made and in this way the robot can work the piece.

The usage of hybrid programming is a very practical way of increasing flexibility in production and thereby increasing the effect of robot manufacturing. In the same manner rearrangement time can be substantially reduced, allowing for cost effectiveness in production of even small batches.

Example of hybrid programming

The following is an example of a typical welding task in which the product is placed at an appropriate location in the workcell and the robot carries out a number of weldings. The flow of work for the programming is according to the open system model ^[1], illustrated in figure 1.

Design Planning Production

The product has been constructed in a CAD system Off-line programming in Ropsim Welding by Robot.

Figure 1. Open system model

The product model including support positions for programming is created in the Cad system and imported in Ropsim. The Off-line programming part consists of the following activities:

Placement of locations (position and alignment) that the robot shall move according to. The movements of the robot are determined by the process and the limitations of the robots movement range together. Determination of movements and sequence.

Program code generation for robot specific languages such as Reis robot language.

Program verification and debugging. In this part simulation, 3D visualization and other tools are used. The simulation runs through the determined movement sequences after which any errors are corrected.

After the verification of the robot program in the simulation the program is downloaded to the robot. On-line programming is used to adjust an appropriate number of locations. These adjustments can be avoided if the piece has not been relocated further than the sensors can handle.

The robot program then uses the adjusted locations and moves the off-line programmed task to it's correct place.

Screenshot from Ropsim

[1] Trostman E., Conrad F., Trostman S., Nielsen L.F. (1992) Robot Off-line programming and simulation as a true CIME subsystem. IEEE International Conference on Robotics and Automation.

Conclusion

The right combination of programming methods allow for a very effective programming and a quick rearrangements of production. An up-to-date developers environment such as Ropsim supports the usage of a combination of on-line and off-line programming techniques.

The cost of on-line programming is equivalent to the production value, whereas off-line programming has no expenses other than that of a programmer and the off-line programming tool. As production value is likely to be somewhat higher than that of off-line programming more time can be used in planning supported by off-line programming than is possible with on-line programming.

In most cases off-line programming is much faster than on-line programming, leading to substantial cost reductions by using off-line programming.

The correct combination of on-line and off-line programming therefore leads to cost reductions in production adjustments. This implies that the limit of when a production adjustment is remunerative is moved considerably. Or, to put it in other words, production simply becomes much more flexible.