Adding Inverse Kinematics > Joint Map
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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:
- 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.
- 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).
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Redefinition of Travel Limits
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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.
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