Human Performance in Six Degree of Freedom Input Control

Shumin Zhai, Ph.D.

2.6 Descriptions of the Four Techniques in Experiment 1

This section provides brief descriptions of the four input techniques used in Experiment 1. More formal and detailed descriptions of these input schemes are provided in Appendix 1.

2.6.1 Isotonic Position Control

The physical interface for the isotonic position control condition in Experiment 1 was the MITS glove, designed and built by the author. An Ascension Bird^TM magnetic tracker was attached to the centre of the palm of the glove, the rotational centre of the hand. Also mounted on the palm of the glove was a clutch with a T-bar. The clutch could easily be pressed down by closing the fingers (Figure 2.5).

While using the isotonic position control technique, the user operated the input device in one of two interaction states. When the userÌs hand was open, the hand movement did not have any effect on the cursor. When the userÌs hand was closed (by pressing the clutch down), the controller became engaged and the manipulated object would be slaved to the hand motion. The operation of the isotonic position control technique is described more formally and in more detail in section A1.1 of Appendix 1.

2.6.2 Isotonic Rate Control

The isotonic rate control was similar to the isotonic position control (two states), but the cursor velocity, rather than the cursor position, was proportional to the hand displacement. The more a user's hand moved after closing the clutch, the faster the cursor moved. Objects stopped instantly after the clutch was released (see A1.2 in Appendix 1 for detail).

2.6.3 Isometric Position Control

The 6 DOF isometric sensor used in the experiment was a Spaceball^TM (Figure 2.6), manufactured by Spaceball Technology Inc., Boston, MA.

With the isometric position control scheme, the user also operated in one of two interaction states. The button on the Spaceball (situated beneath the membrane of ball at the front) was employed to switch between the two states of operation. When the button was pressed, the controller became engaged and the cursor's movement was proportional to the force/torque that the user applied to the ball. Once the button was released, the cursor remained where it was. The user might have to switch between the two states several times in order to move the cursor over large distance without exerting excessive force/torque. The operation of the isometric position control technique is described more formally and in more detail in section A1.3 of Appendix 1.

2.6.4 Isometric Rate Control

The isometric rate control was a single state scheme. The objectÌs velocity was proportional to the force/torque applied on the Spaceball (see A1.4 in Appendix 1 for detail).