Below is a view of the different ways the haptic device can be implemented. The haptic device can have a feedback which is localised as in the vibration of a mobile handset. It just intimates that your attention is needed and you have to look for it. It does not have any direction to point you in any particular direction for your attention. Some devices can apply forces in a particular direction or vector. That is they can apply force in a 3D space of a particular size. These can be used to guide robotic arms in 3D space while knowing what are the forces being applied by the end effector. Sometimes more than one type of sensory input may be used to increase the feel factor which we call the multimodal interaction method. The haptic information can be used as the primary source of information to control your system or can be used as secondary information channel. Secondary signals may be like warning signals that a potential dangerous situation is being approached. The warning tone on your PC when you do some wrong command with your mouse is a prime example of secondary haptic audio information being provided by your ears.
Q. What are the key components in an haptic-based system?
A. The key components would be actuators, sensors, effectors, controller and drive circuits, it’s software and displays for the user interface. Different types of actuation mechanism can be used to stimulate different types of sensory inputs to the human body. For example electrostatic technology can be used to stimulate friction and normal indentation. Piezoelectric technology can be used to stimulate normal indentation, lateral skin stretch and vibration. Similarly a particular feel can be stimulated by different technologies. For example normal indentation can be stimulated by electrostatic, piezoelectric, motor, shape memory alloys, electromagnetic micro coils, air jets, pneumatic valves and dimples, acoustic radiation pressure and electro stimulation.
Q. What are the main design parameters for haptic effect?
A. The main design parameters for haptic effect are:
1. Duration: How long the haptic effect will last
2. Envelope: It is the area that bounds the attack and fade portions of an effect (how the effect starts and ends) and allows you to change the level of the effect over its duration.
3. Magnitude: The strength of the output of the sensory perception actuator
4. Period: The timing between the sensation pulses.
5. Phase: It sets the point at which the effect begins with respect to an event.
6. Wave form: The shape of the repeated sensation pulses.
Q. What are the key design challenges in designing a haptic-based system?
A. The main challenge in designing the haptic device is to make the control interface to feel exactly like the tool being used originally by the operator. Take the case of a haptic device that mimics the tools of the Endoscope Surgeon. The haptic device has to feel like a normal endoscope. The actuators and sensors have to be implemented to look almost like that. The major issue would be balancing the weight of the different actuators etc. along the different axis so that the surgeon feels exactly like his original equipment. Another design aspect would be to provide the kinetic motion and freedom exactly like he would feel while conducting the said operation on an actual patient. It is also very important to make the software and control mechanism fast and accurate.
Q. Could you talk about an interesting technical challenge that your design team faced recently?
A. When we were designing the haptic device for surgical simulation, one of the major challenges was balancing the weight of all the mechanical components and nullifying the imbalances of the weight. When an actuator is used, it adds weight to the device. So we had to design the structure in such a way that they all cancel out. The second part of it was that we wanted to give it a natural motion path to the operation of the device. If endoscopic operation is considered, we have to actually follow a path that a doctor in actual situation will take. So the whole device has to be made as if the doctor feels that he is actually operating. We had to juggle the mechanical designs and the software feedback in such a way that we had to actively overcome the weight with the software. It was challenging but one fine day the idea clicked that the whole thing can be done. We came up with a device which had 5 degrees of motion out of which only 1 degree of motion had to be actively stabilised whereas the remaining 4 degree were naturally stabilised as far as the weight and friction were concerned.