18-04-2011, 09:29 AM
presented by:
JOBIN BENNETT
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Abstract: 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, relatively low cost and its simplification 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.
I. INTRODUCTION
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.
II. TECHNOLOGY
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.
1. FREE SPACE MUST FEEL FREE
There cannot be any external forces present and there must be low inertia and little friction. The Phantom system.s friction is measured at less than .1 Newton (Nt). For inertia a user feels no more than 100 grams of mass and the unbalanced weight is less than .2 Nt at all points in the workspace.
2. VIRTUAL OBJECTS MUST FEEL STIFF
The second criterion is that the virtual objects must be perceived as stiff. The virtual object or surface can only be as stiff as the control algorithm allows it to be. The maximum stiffness is about 35 Nt/cm. Although according to Massie and Salisbury, most users will be convinced of a stiff surface at 20 Nt/cm. Sound is also a factor in the stiffness of virtual objects. If a user touches a hard surface and they hear a knock; the user is likely to accept the surface as stiff.
3. VIRTUAL CONSTRAINTS MUST NOT BE EASILY SATURATED
The third criterion is that virtual walls must be solid or immovable to the user. This means that the force exerted by the user must be counteracted by the phantom system. The maximum force the system can exert is only 10 Nt of force. However, it has been shown that during precise manipulation a user exerts 10 Nt or less of force, but on average a user only exerts 1 Nt of force, while maximum continuous force capability for the phantom is 1.5 Nt . Therefore, the system is capable of responding to regular manipulation activities. The phantom needs to match the human sensory, motor and cognitive systems. The system does not have to completely replicate a normal human being but the touch sense is harder to replicate than vision or hearing. A good example is that to match human vision only 30 to 60 frames per second are needed for the viewer to believe constant motion. Human touch is far more sensitive and therefore the motors. information must be updated 1, 000 times per second to provide a continuous feeling.
III. ADVANTAGES
• SMALL SIZE
The way that the phantom haptic interface has been designed gives it advantages over other haptic devices. Its size resembles a small desk lamp and its workspace is about the size of a mouse pad. The size gives the user the ability to work with the device on their desktop while still having enough workspace to use it freely.
• HIGH FIDELITY
Exoskeletal devices do not allow this much freedom of motion while at the same time having high fidelity. For example,gloves provide more degrees of freedom but with less precision. The system operates on point contact and has much higher fidelity; therefore it can be used for highly technological applications.
• WIDE RANGE OF APPLICATIONS
The phantom setup allows the stylus or thimble to function as surgical tools, paint brushes or other tools depending on the application. Other devices do not allow for such wide ranges of use.
• LOW COST
Phantom is a low cost device.so it is widely used when compared to other haptic devices.
IV. DISADVANTAGES
There are certain problems and limitations present with haptic interfaces. Until recently, research has concentrated on the devices themselves. Now however, software developers are working to meet the needs of these haptic devices. For most haptic interfaces the software is included in the complete setup. Haptic models require much more computing power than computer graphics programs. Haptic options have not been designed into the software and it is nearly impossible to integrate haptic features into existing software packages. This makes it difficult because new software programs must be written.
V. APPLICATIONS
One of the greatest advantages of the Phantom haptic
interface is that it has a wide variety of applications
1. MEDICAL FIELD:
One of the first broad applications is in training people to perform real world tasks. In the field of medicine, touch is an important sense. It has been one of the most researched topics in haptics. Medical students need to train in performing procedures usually done on live patients, gaining skill as time goes on. The phantom provides these students with the ability to train on surgical simulators. This reduces the training time of the students and allows them to train on more complex operations before actually operating. The simulation could be recorded and later observed for evaluation or skill level verifications on the procedure. The surgery can also be recorded so that the student can feel the doctor’s prerecorded procedure. The phantom is ideal for minimally invasive surgeries like laparoscopy and arthroscopy in which the doctors must insert long tools with cameras to view the operation. In these procedures there is no direct contact. The phantom’s setup, precision and high fidelity can greatly enhance the quality of these surgeries.
2. 3D MODELING
3D modeling or clay modeling gives users the ability to work with a virtual surface or ball made out of digital clay. Complex shapes can be created or manipulated. The difficulty of the interaction with the physical world and digital world has kept many designers working with the more familiar, real clay models. The first, major computer animation movie Toy Story began to change this, but still the designers modeled with clay before digitizing. The digitization process is very difficult due to possible errors. For this reason modelers want a new system. Industrial designers and modelers can benefit from the application because 3D modeling packages have many benefits over classic software for four main reasons. Touch providing feedback helps to position the object correctly in 3D space, it helps make the visualization clearer by letting the user feel the models, and assists in the communication of the physical properties of the model. The fourth reason is that force feedback lets users continuously manipulate the objects. The programs will then let the
designers work with more creativity.
VI. FUTURE SCOPE
In the future, it could be possible to have virtual rooms where about 10 to 40 people gather to share in graphic and haptic displays. With one or two people in one virtual room, a class could explore molecules, sculpt in a ceramics class or participate in any class that involves models that need to be manipulated, passed around or touched. Demonstrations of multiple finger interactions are expected with or without multiple user interactions with haptic devices. Sensable Technologies will deal with stability during tasks that involve two fingers to grasp objects and with tool interactions such as screwdrivers and pliers. The future of haptics depends not only on technical advances but also the understanding of how to convey the information correctly and precisely. In this paper, I have explained the Phantom haptic interface and the collision detection pseudo-code to understand the haptic interactions at a lower level. I have showed the many advantages and applications of the phantom system that far outweigh the drawbacks of the limiting factors and problems. Even though haptics is a new field, I believe it will come to have a much greater role in commercial applications in the years to come.
VII. CONCLUSION
The development of the PHANTOM device has demonstrated the feasibility of a relatively low-cost system which can provide convincing sensations of interactions with virtual object. The relative ease with which users can learn to use the device and immediately begin perceiving and rearranging virtual objects suggests that we have crossed an important performance threshold. Performance which permits distinct sensations of free space and constrained motion results from a proper balance of mechanism properties such as friction, inertia, force, resolution and bandwidth. It is an important research question as to how this balance scales with the size of the interface workspace. Larger versions of the PHANTOM are under development and will help in determining the appropriate balance of performance qualities needed at new scales. The PHANTOM is currently in use in several labs at MIT as well as a number of government and industrial research labs. We expect in the near future to see demonstrations of multiple finger interactions and multiple finger interactions and multiple user interactions in shared workspaces with the device. Our own work will focus on the stability and programming issues which arise when two fingers grasp objects to perform assembly tasks as well as use of the device to permit tool interactions such as screwdrivers and pliers.
