Multidirectional Bending Robotic Device Using SMA Wires for Precise Laser Irradiation During Transurethral Lithotripsy

概要

The complex and elaborate structure of the urinary system presents surgeons with difficulty
in using a ureteroscope with a fixed optical fiber to reach the targeted calculus. To address this
challenge, a robotic device is required to control the direction of laser irradiation position
independently in ureteroscopes. To facilitate the usage of the device, an automatic control
system with high precision and fast response is desired in this research.
A continuum robotic device was designed and fabricated. The device is constructed with
three slackened shape memory alloy (SMA) wires to control the laser irradiation position of
the optical fiber combined with the view of the camera on the tip of the ureteroscope.
Kinematics analysis and experimental evaluation reveal the capability of the device.
The structure of the device is the same as a single-joint continuum robot. This device is
unique because of the tiny diameter of 1.1 mm which can be used inside the ureteroscope
through a Ø1.2 mm inner channel into the kidney for transurethral ureterolithotripsy. Kinematic
analysis revealed the relationship among space coordinates, angles of bending, and direction
and SMA wires length. The maximum bending angle was around 25°when the current value
was 350 mA on a single SMA wire in the air atmosphere. A better performance was derived in
the water environment in which the bending mechanism rendered over 30°with a current value
of about 800 mA. The device could achieve multi-directional bending by allocating the values
of current on SMA wires, separately. This device offers a major advancement in small size and
dexterity in medical robotics. Combined with a proper control system, this device could
simplify the operation and improve the efficiency of the transurethral ureterolithotripsy.
The control system obtains the feedback information from the visual system consisting of
1 or 3 cameras in different conditions. A control model within the PC is to process the feedback
and outputs the control signal to MCU for the adjustment of the current value. The MCU and
current sensor construct an independent adjustable constant current supply with PID control.
The whole system could ultimately position the optical fiber towards the stone target by itself. ...

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