Device Building (DBG) - P2

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Documentation

Adding Inverse Kinematics > Joint Map
The DOF expression governing the joint.

The joint map expression is used to express the command value as a function of the joint value. In most cases, this expression is a one to one mapping. (For example, Command 1 will be expressed as dof(1), and so on.)

For more advanced usage, the Joint Map can be used for cases where the actuator commands are different than the actual joint value. Two such scenarios are as follows:

  1. In the case of a back link robot, the actuator command joint is different than the joint in the main kinematic chain and should be expressed as a function of the joint values in the main kinematic chain. For example: Command 3 could be written as dof(2)+dof(3), which means Command 3 is the sum of the values of Joint 2 and Joint 3 in the kinematic chain.
     
  2. Another use is in cases where the travel limits of the command value are not in the range of (-180 to +180 deg). Since the Joint value outputs from the inverse kinematic solution are always within the range (-180 to +180 deg), the command value can then be expressed as a function of the joint value to take account of the shift in the travel limits. For example: to express Command 1 in the range of (-90 to +270), use the expression: =dof(1) + inrange(dof(1),-180*RAD,-90*RAD)*(360*RAD).
Redefinition of Travel Limits

If the design of the mechanism is changed (by adding or removing a command or changing the joint type, for example) the limits will reset to the design values.

The correct method of creating a mechanism is to add all of the joints and commands and then modify the travel limits. If the definition of the mechanism has changed such that the limits are affected, a warning message is displayed when Travel Limits is launched and the limits will need to be examined to ensure that they are correct.