PHANTOM, means Personal Haptic Interface Mechanism, was developed at MIT as a relatively low cost force feedback device for interacting with virtual objects. Phantom device is a robot arm that is attached to a computer and used as a pointer in three dimensions, like a mouse is used as a pointer in two dimensions. The PHANToM interface's novelty lies in its small size, information. The device has enabled users to interact withand feel a wide variety of virtual objects and will be used for control of remote manipulators.Rather than displaying information from many different points, this haptic device provides high-fidelity feedback to simulate touching at a single point. It just like closing your eyes, holding a pen and touching everything in your office. You could actually tell a lot about those objects from that single point of contact. You'd recognize your computer keyboard, the monitor, the telephone, desktop and so on. Most phantom haptic interfaces use three degrees of freedom, which makes the force-feedback system more precise giving it advantages over other haptic devices. Collision detection is an important issue for the interaction between the thimble or stylusand the object. Applications include medical simulation for training in surgical procedures and three-dimensional (3D) paintor 3D clay modeling for designers.
The PHANTOM is a convenient desktop device which allows users to reach beyond the “Looking –Glass” of exixting computer monitors, and actually touch virtual objects represented within the computer.Users connect to the mechanism by simply inserting their finger into a thimble.PHANTOM device is a robot arm that is attached to a computer and used as a pointer in three dimensions,Like a mouse is used as a pointer in two dimensions.It just like closing your eyes,holding a pen and touching everything in your office.The device has enabled users to interact with and feel a wide variety of virtual objects and will be used for control of remote manipulators. New users of the high technology haptic
interfaces are very surprised and intrigued with the reality of the their experiences. A blind user was fooled when he was able to touch a virtual object. He examined the virtual object.s surface with his finger and was not surprised at all until he was reminded that there was no physical object present. This startled him because he jumped and started reaching out for the nonexistent object with his other hand. Another example that shows the reality of the experience is the demonstration of a medical procedure. A needle biopsy is a procedure in which a doctor inserts a long needle into the brain. When this procedure has been demonstrated using a haptic device, many doctors’ reactions are that the needle seems a bit dull.This means the doctors are more concerned with the procedure than they are concerned that it is only a simulation. The reality of the simulation is also shown when there is a sudden removal of a certain haptic device simulation. It is explained as being similar to when a person who is going to sit down is unaware that the chair has been pulled out. Haptic interactions give the user the illusion that they are dealing with real, physical objects. Interactions to this extent of reality in this new field are motivation for this topic.
The PHANTOM is a convenient desktop device which provides a force-reflecting interface between a human user and a computer. Users connect to the mechanism by simply inserting their index finger into a thimble. The PHANTOM tracks the motion of the user’s finger tip and can actively exert an external force on the finger, creating compelling illusions of interaction with solid physical objects. A stylus can be substituted for the thimble and users can feel the tip of the stylus touch virtual surfaces. The phantom allows the user to interact with a variety of virtual objects. The device exerts an external force on the computer user with force feedback that gives the illusion of interaction with solid physical objects. Figure1 one shows a typical phantom device.The phantom is an electromechanical desktop device that connects to the computer’s input/output port. The user inserts a finger into a thimble or holds a stylus supported by a mechanical arm. The thimble or stylus will then track the motions and position of the user’s Finger tip while applying forces on the user.
The phantom system is controlled by three direct current(DC) motors that have sensors and encoders attached to them. The number of motors corresponds to the number of degrees of freedom a particular phantom system has, although most systems produced have 3 motors. The encoders track the user.s motion or position along the x, y and z coordinates and the motors track the forces exerted on the user along the x, y and z axis. From the motors there is a cable that connects to an aluminum linkage
which connects to a passive gimbal which attaches to the thimble or stylus. A gimbal is a device that permits a body freedom of motion in any direction or suspends it so that it will remain level at all times. As explained later in the paper, because the three degrees of freedom meet at one contact point, no torque is measured, only force applied to the point. Friction and inertia must be constant to limit distractions of the user. Also, the haptics system must be able to analyze and sense the forces applied by the user and then deliver the sensation back in real time.The phantom was designed under a few important considerations, first among them being: In the physical world we impose forces on ourselves whenever we touch anything. These forces and the position and motion of our hand and arms are transmitted to the brain as kinesthetic information. This information along with cutaneous (touch) senses, force and motor capabilities are what allow us to touch and manipulate objects and relate them to the space around us. The phantom haptics system must also be able to interpret force and motion information. It must be able to determine how objects move when forces are applied and also determine the geometry of the object (texture and friction of the surface of the object). Events tracking the change in position or motion of the probe, collision detection between the object and another object or the probe, explained later in the paper, are all important. The Phantom was designed with three degrees of freedom because very little torque (twisting-rotating) is involved with either the thimble or the stylus. Degrees of freedom are the directions the user can move in. For a user to touch all sides of a virtual 3-dimensional object the haptics system needs 3 degrees of freedom. Another 3 degrees of freedom are needed if a user wants to rotate the object freely. Because the first Phantom haptic interface that was created uses only 3 degrees of freedom, it allows the system to model those 3 degrees of freedom as a point contact in the virtual environment. This simplifies programming because with a point contact there is little torque, therefore it is less complex. These considerations were combined into three main criteria to attain a balanced, effective system.