Virtual Reality: Touch/Haptics

Creation of Haptic Virtual Objects

Generally, HVOs are created through force fields (or “force-feedback”), generated by computer-controlled mechanical systems called haptic interfaces (HIs). An HI delivers the force-feedback to a person's hands or body. This reproduces major aspects of what actually happens when touching real, everyday objects.

For example, in Figure 1(a), a person handles a stick to poke and deform a real (not an HVO), flexible surface (e.g., a rubber sheet). Following the physics of this mechanical interaction, the surface exerts a force back into the stick. This contact force is transmitted to the person's hand. The person experiences this force as the surface's resistance to deformation. This interaction scenario can be reproduced with an HVO. For this, the person holds an HI's sticklike manipulandum (Figure 1b). The rest of the HI mechanism is only partially shown (the bar connected to the manipulandum's tip, Figure 1b). The person moves the manipulandum in an empty, delimited, three-dimensional space (the HI workspace). HVOs are created within this workspace. The person uses the manipulandum to “poke” an HVO (dashed surface, Figure 1b). The HVO is not a physical object at all. It consists only of computer-controlled forces that are generated as follows.

As the person moves the manipulandum, HI's sensors measure the current position of the manipulandum's tip (Figure 1b). A control computer (CC) monitors this position. When the person moves the manipulandum's tip into the workspace region occupied by the HVO, the CC detects this “collision” of the manipulandum's tip with the HVO. Then, the CC calculates a simulated contact force from a model (e.g., equations) of the real interaction's physics. Next, the CC activates the HI's actuators (e.g., electric motors) that, in combination with HI mechanics, produce an actual physical force that is applied into the manipulandum's tip (Figure 1b). This force physically realizes the simulated contact force. As when touching the real surface (Figure 1a), the person feels HI forces through the manipulandum. As the person explores and even “deforms” the HVO, adequate HI forces sculpt, so to speak, the HVO. This software-controlled HVO creation process is called haptic rendering (HR). The CC executes HR events (collision detection and force calculation and generation when necessary) at a high rate (1 kHz or more). In contrast, graphics rendering typically works at a rate of 30 Hz.

...