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Pneumatic-type Surgical Robot End-Effector for Laparoscopic Surgical-Operation-By-Wire

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Pneumatic-type Surgical Robot End-Effector for Laparoscopic Surgical-Operation-By-Wire

Chiwon Lee et al. Biomed Eng Online.

Abstract

Background: Although minimally invasive surgery (MIS) affords several advantages compared to conventional open surgery, robotic MIS systems still have many limitations. One of the limitations is the non-uniform gripping force due to mechanical strings of the existing systems. To overcome this limitation, a surgical instrument with a pneumatic gripping system consisting of a compressor, catheter balloon, micro motor, and other parts is developed.

Method: This study aims to implement a surgical instrument with a pneumatic gripping system and pitching/yawing joints using micro motors and without mechanical strings based on the surgical-operation-by-wire (SOBW) concept. A 6-axis external arm for increasing degrees of freedom (DOFs) is integrated with the surgical instrument using LabVIEW® for laparoscopic procedures. The gripping force is measured over a wide range of pressures and compared with the simulated ideal step function. Furthermore, a kinematic analysis is conducted. To validate and evaluate the system's clinical applicability, a simple peg task experiment and workspace identification experiment are performed with five novice volunteers using the fundamentals of laparoscopic surgery (FLS) board kit. The master interface of the proposed system employs the hands-on-throttle-and-stick (HOTAS) controller used in aerospace engineering. To develop an improved HOTAS (iHOTAS) controller, 6-axis force/torque sensor was integrated in the special housing.

Results: The mean gripping force (after 1,000 repetitions) at a pressure of 0.3 MPa was measured to be 5.8 N. The reaction time was found to be 0.4 s, which is almost real-time. All novice volunteers could complete the simple peg task within a mean time of 176 s, and none of them exceeded the 300 s cut-off time. The system's workspace was calculated to be 11,157.0 cm3.

Conclusions: The proposed pneumatic gripping system provides a force consistent with that of other robotic MIS systems. It provides near real-time control. It is more durable than the existing other surgical robot systems. Its workspace is sufficient for clinical surgery. Therefore, the proposed system is expected to be widely used for laparoscopic robotic surgery. This research using iHOTAS will be applied to the tactile force feedback system for surgeon's safe operation.

Figures

Figure 1
Figure 1
Control block diagram and experimental flow of the overall system. (a) Interface for surgeon. (b) External arm. (c) Pneumatic gripper system. (d) Surgical instrument. (e) Gripping force measurement system using data acquisition (DAQ) board. All hardware is controlled using the LabVIEW® software based on the state machine structure.
Figure 2
Figure 2
Improved hands-on-throttle-and-stick (iHOTAS). (a) Conventional HOTAS controller. (b) Upper layer of the special housing. (c) Lower layer of the special housing. (d) 6-axis force/torque sensor. All the screws in the special housing assembly were tightly secured to ensure the precise measurement. The improved HOTAS (iHOTAS) controller was used to perform translational movement.
Figure 3
Figure 3
Conceptual design of the surgical robot system.
Figure 4
Figure 4
Design of surgical instrument. (a) Pneumatic gripper. (b) Wrist joint. (c) Elbow joint. Several gears, outer shells, micro motors, and joint link are assembled. This instrument performs elbow, wrist, and gripping motions. The surgical instrument’s length and outer diameter is 300-mm and 8-mm, respectively. Abbreviation: spur gear (SG), spur and bevel gear (SBG), and bevel gear (BG).
Figure 5
Figure 5
Actual surgical instrument. (a) Entire surgical instrument. (b) Zoom in for elbow joint. (c) Zoom in for wrist joint and closed gripper by inflated catheter balloons. The position of the micro motors, several gears, and gripper are presented in this figure. The inflated catheter balloons make gripper close the gripper’s tips by Newton’s 3rd law.
Figure 6
Figure 6
Assembled surgical instrument and external arm.
Figure 7
Figure 7
Pneumatic hardware system. (a) Solenoid valves, speed regulator, and pressure regulator control the compressed air. (b) Air compressor pumps compressed air into the catheter balloon. (c) Air pump sucks compressed air out of the catheter balloon.
Figure 8
Figure 8
Diagram of valve control algorithm. Three valve statuses can be controlled by the surgeon.
Figure 9
Figure 9
Compressed air flow by valve mechanism. (a) Inflow. (b) Stay. (c) Outflow. Three compressed air flow statuses are controlled by SV1 and SV2 between the compressor and the catheter balloons. Abbreviation: solenoid valve (SV).
Figure 10
Figure 10
Kinematic structure of the system.
Figure 11
Figure 11
Gripping force measurement experimental setup using Flexiforce.
Figure 12
Figure 12
Experimental result of gripping force in accordance with pressure during 10 repetitions. The standard deviation of the gripping force was 0.1 N between 0 and 0.775 MPa with 0.025 MPa intervals.
Figure 13
Figure 13
Experimental results versus simulated results. The step function of the simulated result was similar to Figure 12’s experimental result for the gripping force at a pressure of 0.3 MPa.
Figure 14
Figure 14
Block transfer task. Peg task performed using fundamental of laparoscopic surgery (FLS) task.
Figure 15
Figure 15
Workspace of the proposed surgical robot system. (a) Elbow joint (J7) was considered with external arm (J1-J6). (b) Elbow and wrist joints (J7 and J8) were considered with external arm (J1-J6).

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