From the Master's Thesis written by Matthew Kontz:
"Haptic (adj): Of or relating to the sense of touch; tactile. When interacting with a physical object, humans experience a haptic sensation. How the object responds to human touch relays important information back to the human. Assuming the human is strong enough to the lift the object, an inertial force conveys the objectís mass. The texture of an object gives clues about its material properties. The stiffness can also be meaningful. If the object is really stiff it feels immovable like a rock wall. Humans are constantly gaining insight into their surroundings through haptic feedback.
In the field of haptic robotics these interactions are mimicked using robotic arms. Varying the forces displayed by the robotic arm can generate haptic sensations. A viscous sensation can be implemented by displaying a force that is proportional to the velocity of the userís hand. If the force is proportional to displacement then the haptic robot feels like a spring. A stiff one side spring can be made to feel like an immovable surface such as a hall. With the evolution of computers the possibilities of creating haptic sensation have increased due to the ﬂexibility and power of modern computers. It is even possible to create virtual environments that only exist inside a computer.
Haptics have also been used to manipulate remote devices. This is known as bilateral teleoperation. Teleoperation means to control a remote device. The word bilateral implies that both objects are interacting with each other. Ideally the operator would feel an exactly scaled version of the force exerted on the tip by the physical environment. One example of this is the Canada arm on the Space Shuttle. In this project a less exotic class of remote manipulators are explored, hydraulic construction equipment. More specifically a hydraulically actuated lifter is used as the remote device in this project. Currently, most heavy machinery such as loaders, excavators and lifters are controlled by an operator manually opening and closing valves. With practice it is possible to master the art of manipulating the end eﬀector. However, this takes a lot of time and practice.
Using haptic control brings a lot of possibilities to the table. Perhaps the most important is the ability to make the end eﬀector mimic the motion of the userís haptic input. Haptics forces can be produced to make sure that the master device does not get too far ahead of the slave manipulator. This means that there can be a proportional relationship between the humanís movement and the movement of the bucket. This makes it easier to manipulate the remote device.
Having the slave follow the master can present a problem if the slave is a non-holonomic object such as a forklift truck and the master is a holonomic serial robot. It is possible for the master to exceed its workspace before the slave has reached its target due to the fact that the slave can drive anywhere and the master has a ﬁnite workspace. A solution to this problem is to use a rate controller. This means that the rate change of the slaveís position is proportional to the position of the master. While manipulating an object it would still be nice to be able to switch into position control mode where the movement of the slave mimics the master. Using a controller that can switch between these modes is a solution that uses the strength of both of these control techniques.
Other haptic forces can also be used to convey other useful information back to the operator. When the end eﬀector picks up an object, force feedback can relay the mass of the objects back to the operator. If the end eﬀector was to run into an immoveable object this can also be relayed back to operator.
Not only can forces be reﬂected to the user, but virtual forces can be created as well. For example if it is undesirable for the remote device to enter into a certain area, virtual constraints can be used to stop the master device from entering these areas. If the master cannot enter these restricted areas then the slave cannot be commanded to enter into them. This project describes some haptic effects that can be used to enhance operator control of hydraulic equipment using haptic feedback.
Another great advantage of using haptic control to manipulate hydraulic equipment is the possibility of combining the strengths of human intelligence with the computational power oﬀered by computers. The humanís ability to process information and make decisions cannot be replaced by computers. At the same time computers have the ability to process simple tasks such as math at an amazing rate. Computers can be used to quantify things such as position and force and use this data for tasks such as obstacle avoidance. Haptics can combine human intelligence with a computerís ability to systematically control a remote object."