A Miniature Hydraulic Parallel Manipulator for Integration in a Self-propelling Endoscope

1. A Miniature Hydraulic Parallel Manipulator for Integration in a Self-propelling Endoscope By Sandeep Manukonda

2. An Overview • Objective • Introduction • Miniature Manipulator Design • Prototype and Tests • Valve integration • Conclusion & Future work

3. Objective • To present a miniature robotic manipulator that will be integrated into a self-propelling endoscope. • The endoscope is meant to inspect and intervene in the human colon through which it moves by inch worm motion and is designed as a Stewart Platform and driven by three hydraulic pistons.

4. . • Fig 1 Stewart Platform • Figure 1 shows the Stewart platform. It is also known as hexapod positioner and is a kind of parallel manipulator. Here the length of the legs are changed to position and orient platform.

5. Introduction • In the present medical field colonoscopes are semi-flexible tubes which have to be maneuvered into the colon by pushing. • As the colon is very elastic and has multiple bends it require skilled surgeon to perform the operation. • The alternative for this is self-propelling robot.

6. . • Fig: 2 Self-propelling robotic endoscope • As shown in figure 2 the robotic endoscope consists of two clamping modules connected by an expansion/contraction bellow. The miniature is placed at the front of the endoscopic system, which is used to orient and position the tools and camera.

7. Contd… • Manipulation of the tools require a manipulator with high force output. • Actuators that generate high forces are Shape Memory Alloy (SMA) and hydraulic actuators. • Problems with SMAs are the slow response, difficulty in controlling, and the heat losses. • Hydraulic manipulators don’t have these problems except the driving power.

8. Miniature Manipulator Design • The design of the manipulator is based on a 3 degree-of-freedom (dof) stewart platform. • Figure 3 shows the design of the miniature hydraulic manipulator. It has an outer diameter of 12mm and a length of 30mm. Fig: 3 Manipulator Design

9. Contd.. • The platform is driven by three hydraulic pistons which are connected to the upper platform through ball joints. • The system can be extended to a 6-dof manipulator by placing two of these Stewart platforms in series.

10. Prototype & Tests • Figure 4 shows the exploded view of the prototype parts. Fig: 4 exploded view of prototype

11. Contd… • Figure 5 gives the enlarged view of piston. • The piston rod has a square section which slides into a sleeve of the guide plate. Fig: 5 Leg Prototype

12. Tests • The kinematics of the hydraulic manipulator work well and the construction is rigid and stiff. • The rotation of the manipulator is limited to 30-35 degrees. Fig:6 Miniature in two extreme positions

13. Contd • Further measurements have to be performed on the positioning speed and accuracy, and on the forces generated by the system. • Therefore, valves and a measurement system have to be added, and a control loop has to be closed around the system.

14. Valve Integration • The number of hydraulic tubes should be as low as possible to keep the tail of the self-propelling endoscope as flexible. • To reduce the number of the tubes, valves can be integrated into the manipulator or endoscopic system.

15. Piezoelectric valve • Figure 7 shows the design for piezoelectric valve. • The heart of the valve is formed by a steel ball, which is pressed onto an orifice. • When a voltage is applied to the piezo, it elongates and closes the valve. Fig: 7 Piezoelctric valve design

16. Electromagnetic valve • Figure 8 shows the construction of a valve based on the electromagnetic reluctance force. • The magnetic path is formed by the central pin, valve block, the upper plate and air gap between pin and plate Fig:8 Electromagnetic valve design

17. Contd.. • When a current is sent through the coil, magnetic flux flows through the magnetic circuit and thus also through the air gap. • The reluctance force tends to close the air gap and attracts the pin towards the upper plate, thus closing the valve. • As the valve closes, the air gap becomes narrower and the attracting force increases.

18. Conclusion & Future work • A miniature hydraulic Stewart platform is built for use as a manipulator for a self-propelling endoscope. The manipulator works very well and shows a high stiffness. • Problems with friction will be solved by redesigning the O-ring seals. Piezoelectric and electromagnetic valves are developed which should be integrated in the actuator block to reduce the number of hydraulic connections. • Tests will show which of the valve types has the best characteristics. • Finally, position sensors, a control loop and an elastic cover will be added.

19. References • Control sensors and actuators By C.W. deSilva. • A miniature Hydraulic parallel manipulator for integration in a self-propelling endoscope By J. peirs, D. Reynaerts "A miniature hydraulic parallel manipulator for integration in a self-propelling endoscope"

20. . Thank you Any Questions?