In the previous sections, the features of GPL that were described closely mimic those that are found in other object orientation variants of the Basic Language. Those features included arithmetic expression representations, control structures, variable types and declarations, mathematical functions, etc.
In the next sections, the features of GPL that have been added specifically to provide built-in motion control facilities are described. Consistent with the philosophy of object-oriented languages, these special features are provided as properties and methods of built-in “Classes”. In some cases, the Classes are global system classes that simply serve to group features together as an aid in accessing and understanding these facilities. For global Classes there is a single copy of the Class. The Math Class that was described earlier is a good example of a global system class. In other cases, the classes have multiple instances (objects) that allow programs to have multiple copies of the objects, each with their own independent set of values for properties and methods. For example, in a Visual Basic program, the “Textbox” is a good example of the use of objects. An application can have multiple Textboxes each with different colors and sizes and other visual effects. In a motion application, robot locations are represented as objects to allow an application to store multiple robot and object positions, each with its own special properties.
Table 19-12 describes the motion control specific classes that are included in GPL. Each of these classes is discussed in more detail in the following sections.
| Motion Control Class | Description |
|---|---|
|
Signal Class (Global) |
Reads and writes digital, analog and other simple means of input and output |
|
Location Class and Objects |
Defines positions and orientations of the robot and objects |
|
Profile Class and Objects |
Defines sets of parameters that specify the trajectory to be followed when moving between Locations. |
|
Move Class (Global) |
Provides the basic methods for executing a motion between Locations using Profiles. |
|
RefFrame Class and Objects |
Defines robot and part reference frames that can automatically alter the total (absolute) positions and orientations of Locations. |
|
Controller Class (Global) |
Provides access to general facilities provided by the motion control hardware such as power control, timers, etc. |
|
Robot Class (Global) |
Provides access to the attributes and properties of each robot such as their current position and homing methods. |
For many simple pick and place operations, only the first four basic classes need be utilized, i.e. the Signal, Location, Profile, and Move Classes. The facilities provided by the more advanced Classes (RefFrame, Controller, and Robot) can be brought into play as an individual becomes more familiar with the system or as applications become more complex.