Haptic Interface

The main components of the HI will consist in the following elements:

• A robotic device;
• A control unit which implements the basic control for the HI.

As a result of the user analysis, based on the mock-up evaluation and on the user survey, the robotic device is made of two similar mechanical arms with a serial kinematics having 3 DOF (2 rotational, 1 prismatic), and 3 rotational passive and sensorized joints.

Such a system will be able to allow motion of the user hand in a large portion of the operative space. For design constraint the interface will be able to operate within the space allowed in a CAVE and without interfering with the sidewalls and the floor. The two haptic interface will be composed of:

• Two mechanical arms designed and optimized for replicating force feedback at the level of the user hand;
• A set of three motors/ sensors for the dynamic control of the arm position, exchanged force;
• A couple of styluses with a button which allow free movement of the hand while exerting forces along the three Cartesian axes.

In order to improve the transparency of use of the device (i.e. to decrease the disturbance forces exerted by the Haptic Interface on the user during free motion), the following technical requirements have been adopted for the design of the robotic device:

• Low mass of the moving part that means a low perceived inertia;
• High stiffness of the structure;
• Low friction;
• High bandwidth force feedback.

The HI is designed in order to allow a large workspace (a parallelepiped of 700x600x600 mm) and to exert a continuos force of 10 N and a pick force of 40 N. The robotic device will be powered and controlled by means of a dedicated unit (the control unit). Such a control unit will be capable of:

• Providing power supply for motor control;
• Sensorizing the arms;
• Actuating the arms;
• Providing an open loop (pre-compensated) control for exerting forces on the user fingers.

Moreover the control unit will provide the required real time support for providing basic safety issues, ensuring interface (Open Loop) stability, controlling force ranges, configuring and setting up the system. The Low-level controller provides to generate the force stimuli on the user hand and to retrieve their relative position from the physical space.