Table 3.

Robot components and specifications

No.	Part	Description	Parameters
0	robot	4 DOF with optimal workspace for spinal targeting. Pneumatically activated, optically encoded.	Length = 310 mm Width = 240 mm Height = 50 mm
1	coil support	Supports the imaging coils.	Height = 110 mm
2	x-axis actuator	Provides movement in the X direction (left-to-right direction relative to patient orientation). Actuator connected to gearbox. Pneumatically actuated motor with stepdown gear. Non-backdrivable. Motor mounted on translating stage (4); moves the angulation stage (7). Timing belt is the driving mechanism.	Force = 11.7 N Range of motion = 90 mm
3	y-axis actuator	Provides movement in the Y direction (head-to-foot direction relative to patient orientation). Actuator connected to gearbox. Pneumatically actuated motor with stepdown gear. Non-backdrivable. Motor mounted on coil support (1); moves the translating stage (4). Timing belt is the driving mechanism.	Force = 11.7 N Range of motion = 140 mm
4	translating stage	Driven by the Y-axis actuator (3) in the Y direction. X-axis actuator mounted on translating stage moves angulation stage in X direction. Overall, acts as intermediate stage constraining the angulation stage.	X direction travel length = 90 mm Y direction travel length = 140 mm
5,6	angulation actuators	Pneumatically powered motors connected to stepdown gearbox, driving the angulation stage (7), allowing the movement of (8) theta angulation unit which provides head-to-foot rotation (θ) and (9) phi angulation unit which provides left-to-right rotation (φ).	θ rotation: Torque = 1.03 Nm Speed = 2.43 degrees/sec φ rotation: Torque = 0.41 Nm Speed = 6.08 degrees/sec
7	angulation stage	Inside angulation stage are θ and φ angulation units (8) and (9). Timing belts are used to connect (5) and (6) to (8) and (9).	2 DOF
8	theta (θ) angulation unit	Drives the needle guide in the theta direction (θ), as described in Fig. 2. Theta direction is the rotation about the left-to-right axis (which results in head-to-foot rotation).	θ = ±35°
9	phi (φ) angulation unit	Drives the needle guide in the phi direction, as described in Fig. 2. Phi direction is the rotation about the head-to-foot axis (which results in left-to-right rotation).	φ = ±30°
10	needle insertion guide	Needle channel guides the needle to the target in the spinal cord. Driven by (8) and (9) in theta and phi directions.	Insertion depth of 0 to 20 cm below robot
11	image contrast	Diluted gadolinium imaging agent produces visible brightness in MR images, marking the position of the needle insertion guide (10).	Diluted gadolinium