II. Prototype Device

A. New Prototype Imaging Device

Our initial work [24] in designing such an imaging system created a device with 2 cameras and 5-DOF (independent pan and translation axes for each of two cameras plus a common tilt axis). A single camera, 3-DOF version was successfully tested with surgical fellows in a laparoscopic trainer mockup. These quantitative tests using the MISTELS (McGill Inanimate System for the Training and Evaluation of Laparoscopic Skill) tasks [28] showed the device was able to carry out typical minimally invasive surgical tasks equivalent to using a standard laparoscope, with no loss of function[25]. Based upon this design, we have designed a second generation device that improves upon the design of our initial device described above. Our design goals for the new prototype included reducing the device size (from 22mm to 11mm in diameter) and the inclusion of an integrated light source. To reduce the device size to allow it to be inserted through a 12mm trocar, we removed 1 camera and the translation axis. We have also added an LED light source to the device[14]. The total length of the device is about 110mm, and the diameter is about 1 1mm and can be inserted into a standard 12mm trocar.

We make use of modular design to make the device components interchangeable and extendable. The current system includes a user-friendly interface, making it easier to control the camera's DOF using natural motions. It consists of a Pan/Tilt motorized CCD camera with illumination com­ponents, control interface driver, PC, and Joystick controller. After the surgeon anchors the camera onto the abdomen wall, he can use the Joystick to position the camera to the desired surgical viewpoint using the Pan and Tilt motions. The intensity of illumination can be adjusted manually through the control panel. Figure 1 shows images of the implemented prototype device, with integrated lighting and pan/tilt axes.

[Some details are omitted]

B. Zoom Mechanism

[Some details are omitted]

Our zoom mechanism is designed to manipulate the cam­era forward and backward. A rack and pinion mechanism was chosen as the basic mechanical structure for zooming to achieve a compact size (Side View of Figure 3). A 4.5mm miniature stepper motor (0.08mNm maximum torque) is used as the actuator to drive the pinion. The zooming distance is 20mm. The entire zoom package is 12 mm in diameter and 56mm in length. Figure 3 shows the CAD model of the zoom mechanism. It is constructed of a camera module, zoom components and an external shell. To maximize the output torque, 3 sets of gears are used in the design. The 1st gear is a spur gear with 120 Diametral Pitch and 40 teeth. It rotates on a rack, which is mounted on a support which is attached to the external shell. When the motor rotates, the pinion gear travels along the rack, moving the camera module forward and backward along the external shell. A pinion with 120 Diametral Pitch and 12 teeth is matched with 1st gear. 2nd gear(120 Diametral Pitch, 30 teeth) is mounted on the same shaft with this pinion. A pinion with 120 Diametral Pitch and 12 teeth is mounted on the same shaft as the worm. This pinion is matched with 2nd gear. The worm is mounted on the shaft of motor. The ratio of worm gear is 16:1. Finally, we get a total speed reduction of 133:1 with this design, which we are currently testing in animal trials.

Дата добавления: 2014-10-31