Haptic admittance controlled devices are a small sub-species of the of classical haptic displays. The classical haptics displays themselves are a small sub-species of “haptics”.
In a wider sense, “haptics” is the technology that gives a person the sense that they are physically interacting with a remote or virtual world. Haptics was once a hype, but it never took off. It looks like it crashed somewhere in the take-off phase of Gartner's hype cycle.
In all honesty, the killer application has not been found. Still, haptic devices offer a compelling experience of presence in a virtual or remote environment, and maybe their day will come.
This textbook is about admittance control. But it may help to put that into the perspective of the overall haptic experience. This chapter makes that effort. Readers only interested in admittance control itself can skip it.
The most basic kinesthetic interaction with a virtual or remote world is by gestures only, without any physical contact.
Gestures can be tracked by camera or other means, and used as an input to a VR or remote world. This is not haptics, but it comes close enough to deserve a mention. Gestures can be naturalistic, like grabbing a remote or virtual object, or an abstract signal, like in a simple sign language.
Gestures can be made to feel more naturalistic by handling a physical dummy object, called a prop. There is usually no need to make the object a copy of something real. A simple cube is sufficient. It will feel more realistic, and make the tracking easier. In the virtual world, the object can be shown as something more easily related to, like a gripper or a tool.
Sometimes the reaction of the virtual world to the handling of the prop can give a person the impression of feeling a force or a torque. If done deliberately, this is called pseudohaptics. Pseudohaptics can create the impression of feeling of a torque on a freely rotating degree of freedom. This can virtually increase the number of “haptic” DOF’s on a conventional haptics device. The effect can be quite convincing.
Transformation between DOF’s. Levers of a digger or dragline. Controls : steering wheel, rudder pedal.
Actual force feedback can be added to a gripper ( or a joystick ) by a simple passive spring. This is the first step towards actual force feedback, or haptics.
Encountered devices have settable stops on the arms of a passive robot to represent virtual walls. They can even have moveable walls in an open workspace, but this is only possible with careful tracking of the path of an approaching finger, and even then sliding along two orthogonal walls which are supposed to feel like a single diagonal wall will not work. A gripper with an inner end stop settable to the size of a virtual object to be grasped is the simplest, and probably the most useful example of an “encountered” device.
Shape displays, or shape changing objects, are a generalization of the en-countered idea mixed with the passive prop, or possibly as an end effector on a “true” haptic device.
Tangible bits. Phicons ?
TBW. Pin cushion or skin stretch. Can be combined with other types of haptics
The term haptics also seems to cover cell phone buzzers . These buzzers make no attempt to mimic any real life experience. They just give coded feedback as a confirmation of events like sliding over an icon, or pushing a button. Patterns may vary between naturalistic, simulated stick-slip friction or a simulated mechanical button click, or abstract patterns similar to an audio tune, sometimes called “haptic icons”.
Can be used to simulate a ball rolling in a tube and bouncing at the ends, since HF feel is non-directional. Hapticons, phicons.
Admittance control is a natural interface for moving large loads, and it is useful in stroke rehab, although the extra functionality of gently guiding someone's motions may not useful enough to warrant the extra outlay relative to a sandbag and a pulley to lift the weight of the arm.
Whole body motion, Stewart platforms.
Whole body experiences. We will not discuss kinesthetic or tactile interfaces for other parts of the body, if only for prudish reasons.