Life-Size Safer Haptic Environment

Motor-actuated devices are widely used in haptics research and advanced teleoperator masters – capable of creating a rich set of virtual environments in the former and recreating physical environments in the latter. Motors, however, introduce the risk of a device striking or overpowering users within reach. With rare exception, safety concerns limit motor-actuated haptic devices to small workspaces.

The replacement of energetic servo-motors with passive actuators such as brakes improves the inherent safety of the system, and expands the range of motion while still allowing us to simulate virtual objects (i.e. to constrain the user’s motion inside an object). Safety is essential for acceptance in new applications such as medical procedures, quantitative rehabilitation, advanced exercise training, and entertainment. Even if the device experiences a power, hardware, or software failure, a brake-actuated device is inherently incapable of exceeding the kinetic energy that a user supplies in each motion. Using currently available engineering technology, the workspace of brake-actuated haptic devices can expand to cover whole-body movements without risking a user’s safety. With the expanded workspace, a variety of large movements can be trained and quantitatively analyzed.

We have constructed a brake actuated device based on spherical kinematics with a non-actuated 3DOF handle serving as the end-effector. The pitch and yaw axes are driven by backlash and friction free tensioned cable drives, providing an 82:1 torque reduction. The yaw and pitch are capable of ?0 degrees, and both revolute axes intersect within the prismatic joint forming the kinematic center for the device. The prismatic joint can retract to within 0.15 meters of it? housing, with a maximum stroke of 1 meter. Magnetic particle brakes provide torques up to 170N-cm and are situated on all three axes. The device can withstand a user? force up to 222N. The 3DOF handle is dynamically balanced with an asymmetric design. The asymmetries allow for a large range of motion in which gimbal lock is mechanically impossible. The dynamic balancing ensures no off axis rotations will be felt by the user during operation.