3.1. Experiment layout

The monocular vision sensor estimates the cadaver CVJ pose estimation via a 6-UScS manipulator using ArUco-based markers and then transmitted to the manipulator. A set of images were taken from a calibrated vision sensor after the manual actuation of the 6-UScS manipulator was completed. The processed images were used to determine the pose of the Cadaver CVJ after the desired neck trajectory, including lateral bending, flexion/extension, and axial rotation. In radiology, a C-arm is a mobile X-ray machine that can be moved around and adjusted manually to accommodate the desired location for taking X-ray images. The height and orientation of the X-ray camera can be adjusted manually. It was placed around the Cadaver to obtain X-ray images, ensuring the polyaxial screw was adequately secured to the bone.

3.2. Experiment preparation

Initially, the Cadaver was assessed for the absence of rigor mortis. The neck and the head region were exposed without damaging the soft tissues, as shown in Fig. 5(a) following the clinical procedure. The occiput to the (C₅) vertebra was evident for fastening with the experimental setup. The thoracic portion of the Cadaver was positioned on the customized chair in a sitting posture and immobilized by strapping between the two pillars. Following this, the base platform of the MA7DPM, common to the Sarrus mechanism and 6-UScS, was attached to the chair. Coupling and extender screws were assembled with the polyaxial screws to connect the cranium with the manipulator’s top platform, as shown in Fig. 5(b). X-ray images were taken to confirm the proper insertion of polyaxial screws. Finally, the calibrated vision sensor [Reference Basler17] determines the Cadaver’s pose estimation with respect to the base platform.

The ArUco markers are employed to estimate the pose of a Cadaver. A vision sensor and marker(s) provide the pose estimation concerning the stationary base platform, as seen in Fig. 6(a–f).

Figure 6.

(a–f) Vision-based pose estimation of the top platform by inducing the manual actuation.

Figure 7.

Flow diagram for estimating the error in the pose of the experimental setup [Reference Zubair, Kansal and Mukherjee10].

The pose of the marker is estimated with reference to the base fixed frame (B _ff ) as:

(1) \begin{equation} _{\text{Marker}}\mathbf{T}^{Bff}={\left(_{\text{Table}}\mathbf{T}^{C}\right)^{-1}}_{\text{Marker}}\mathbf{T}^{C} \end{equation}

where _Marker T^Bff is the transformation between the cube coordinate system and the base fixed frame, _Table T ^C is the transformation in the coordinate frame fixed to the table and the frame fixed to the camera, and _Marker T ^C is the transformation in the coordinate marker frame and the frame fixed to the camera. Since the table and camera have no relative movement, _Table T ^C is fixed throughout the experiment. After executing the table calibration and estimating the marker pose with reference to the base fixed frame [Reference Babinec, Jurišica, Hubinský and Duchoň18], the pose of the marker is transformed from the camera coordinate frame to the base fixed frame (B _ff ) and then to the platform coordinate frame ( _P T^Marker). The inverse kinematics modules operate with the pose of the marker defined with respect to the plane fixed to the base of the platform coordinate frame. The platform motion is controlled manually by rotating the actuators, and the vision modules run in Visual C++. The kinematic transformation has been established to measure the head motion with respect to the marker position as shown in Fig. 7.

3.3. Experiment and results

Using the screw joints on the legs of the MA7DPM in conjunction with a 6-UScS manipulator allows the user to move in all three directions: lateral bending, axial rotation, and flexion/extension, by activating the screw joints on the legs. This table shows the precise trajectory of the skull used in this experiment and additional information about it. Table I shows the data. In the flexion/extension and side-bending motions performed at their maximum values in a given direction, these modes represent the maximum translation values encountered.

Table I.

The Cadaver’s range of motion.

Once the Cadaver was placed in the experimental setup, a surgical procedure (Odontoidectomy) was performed to remove the odontoid from the C₂ vertebra. Transporal exposure using retainers was used to expose the odontoid for surgery by the surgical team of AIIMS. In clinical practice, the procedure, in general, is performed in a prone position where the Cadaver is placed on the stretcher. It has been mentioned earlier that the experiment requires a sitting posture of the Cadaver, and allowing access was a significant design challenge. Table II shows the load response measured using the experimental setup for the C₁–C₂ rod and screw instrumented in the CVJ region.

Table II.

Load response was measured using the experimental setup for the C₁–C₂ rod and screw implant instrumented in the CVJ region.

3.4. Discussion

The ArUco approach and the ArUco method were used to analyze the process of Cadaver pose estimation using a vision sensor, and the ArUco method was used to accomplish this. This study aimed to determine how well the camera-based measurement performed when estimating the pose faults caused by fixed leg movement (incremental change). This experiment set had its load response measured and analyzed. After conducting two distinct series of tests, it was possible to determine how much load was being measured and, as a result, how much error was being introduced into the load sensor reading.