Characteristics of the Work Space Control

Aside from being the traditional method used, W-space control has some desirable properties:

• Interaction with the physical arm and its environment makes it easier for the operator to visualize the global navigation, such as to determine the next target configuration based on some scene property; e.g. the operator may decide to move the arm such that its left side will be in proximity of some object.
• If the obstacles layout is not of much constraint on the arm motion, this approach can yield very good (near optimal in terms of path length and time taken) results.
• Given the familiar physical layout, it may be easier for the operator to benefit from memorization of motion and improve with training.

However, this type of control also has some serious drawbacks which may outweigh its positive sides:

• In tip-mode, calculating the inverse kinematics becomes progressively more complex and time-consuming as the number of joints increases.
• In a complex environment, the operator may have hard time determining which direction of local motion is better, or whether a given direction leads to a ``dead-end''. This is a serious drawback: for example, in Figure  4 one can pass obstacle with the elbow to the left or to the right; one of those turns out to be wrong as it leades to a dead end, and this would become clear only significantly later.
• From the standpoint of motion planning, a complex environment is not necessarily one with many or with large obstacles; this is much clearer in C-space (see Section  3) than in W-space.

Consequently, W-space control is likely to produce redundant motion: as illustrated in Figure  4, the operator will often try, backtrack, try again, backtrack again, and so on until the passage is found, not rarely through blind luck. This also endangers the arm, as all such motion multiplies potential collisions with surrounding objects. While most people do benefit from a training period in such systems, the training can be costly (in terms of equipment use and damage inflicted on the arm) and time consuming.