Page 64 - Demo

Chapter 462The adjustable frame and holding devicesTo add to the readability of this subsection, numbers put between parentheses are referring to Fig. 2 (numbers 1 to 16) and Fig. 3 (numbers 17 to 32). A framework of a 60 by 60 millimeter aluminum profile (Item Industrietechnik, Solingen, Germany) was designed to mechanically integrate the different components (Fig. 1). The framework is adjustable; meaning the position of the holding devices for the upper and lower jaws can be changed relative to the robot and placed at different heights. This is necessary to mimic clinical circumstances in which the position of the upper and lower jaw are, respectively, vertical and horizontal. For ergonomic reasons, the patient is positioned higher when removing teeth from the upper jaw. The addition of a rotational plate (14,29) between the frame and the holding devices mimics the turning of the patients head and leads to a more clinical representative situation in which the clinician can maintain an ergonomic pose during the extraction procedure. The plate is located just below the FT-sensor (13,28) and can be rotated by pulling a locking bolt (16,32) on the bottom plate (15,30). The locking bolt falls into one of the position holes upon its release and can be further tightened to eliminate any slack. The position holes allow a 137.5-degree rotation in 11 steps of 12.5 degree increment in either direction (a total range of 275 degrees). Next to the ergonomic advantages, the usage of an adjustable frame largely overcomes an important issue of working with a robot arm. When any of the robot’s joints reaches a joint limit, it needs to adjust other joints to enable the end-effector to reach the desired position. This can involve a rigorous movement of the robot, which inevitably leads to some resistance for the clinician. By placing the most relevant joints in a neutral position just before starting the experiment, reaching joint limits can be avoided. This is enhanced by placing the upper and lower jaw in a favorable position relative to the robot arm. The frame was provided with a scale (millimeter) to measure the exact position of the holding devices for calibration purposes, see Section II-D.Essential for reproducible, accurate and thus meaningful measurements is a completely rigid fixation of both upper and lower jaw. Two separate holding devices had to be designed. First because the above-mentioned difference in ergonomic position (horizontal/vertical) of both jaws. Second, because the anatomical differences between the two jaws do not facilitate the design of a single device to fit both. In general, non-corrosive and smooth surface materials were used to facilitate cleaning which is especially necessary when working with (fresh) human material.Tom van Riet.indd 62 26-10-2023 11:59