Avatar Port

Overview

Ports A Port is a haptic device that can receive a representation of a laparoscopic Tool, track its motion and provide force feedback to it. It has a trocar like part in which a representation of a laparoscopic instrument (a Tool) is inserted. The Tool is identified upon insertion. One or many Ports can be used to setup the desired training task or procedure. Each port represents an access point in the simulation. The Ports are populated on a Frame structure that gives them a position that corresponds to the real position. The Ports are connected with a USB-cable, typically to a USB-hub, which is then connected to the simulation PC. Up to 6 ports can be used in a simulation. The Ports are self-powered with batteries, which are charged via the USB-hub.

Communication and power supply

Combine the Haptic Avatar devices and surgical instruments to fit your simulation procedures. Experience the advantage of having force feedback in all motions including the instrument handle. Change instruments by retracting it from the portal and insert another. The type of instrument is identified by the haptic device.

Calibration

When the Port is powered up (with a USB connection) it needs to be calibrated in yaw and pitch. This is done by making a small movement around the yaw/pitch-zero angles. Thereafter, the angles are accurate and absolute with respect to the Port and to the Frame structure it is mounted on. This is only needed once after power up (and never before and between exercises). When a Tool is inserted, it is automatically calibrated upon detection, both insertion-wise and in twist. The simple calibration lets the trainee always focus on the exercise. Another advantage is that if the physical position and orientation of the port is the same as the virtual position of the access portal, a physical tool-tool collision will correspond to a virtual instrument-instrument collision, since the positions are absolute.

Internal feedback loop

The normal force feedback loop is typically 1kHz via the PC, where the simulation program in the PC receives the positions (3 angles and the insertion length), calculates any collision forces and sends them to the Port, which actuates them. A second, complementary method, is to utilize the internal force feedback loop. To do so, the simulation provides a set of primitives, such as spheres, cylinders (capsules), toruses or triangles which all have dimensions, positions, orientations and collision material properties. These primitives can be sent once, and/or updated dynamically. The tool itself is also defined as a set of primitives (upon tool insertion and identification), and the collisions and haptic response can now be calculated internally. The typical internal loop frequency is 15kHz. This is useful when simulating hard surfaces, like bones or tool-tool collisions, and can offload the simulation program in the PC.

Thermal control

All structural parts in the Port are made of aluminum and thereby dissipates the heat from the motors and amplifiers effectively. The Port protects its motors from overheating with an internal thermal control system, which simulates the thermal response based on the dynamic motor loadings. The heat generated in the motor windings dissipates through the motor housings and the aluminum structures around them. When the temperature reaches a certain limit, the maximum allowed power output is gradually reduced. The temperature of the heat sink on the amplifiers is sensed and cooled when necessary with an internal fan. The figure to the left shows a step response where all motor are powered 100% from start, and then 0% at 30s into the simulation. The power output control limits the motor windings to stay below the maximum allowed temperature.