A Novel Axial Force Feedback Device for the Master Manipulator of the Vascular Interventional Surgical Robot

Wei Zhou1, Shuxiang Guo12*, Zhengyang Chen1

1 Key Laboratory of Convergence Biomedical Engineering System and Healthcare Technology, The Ministry of Industry and Information Technology, School of Life Science, Beijing Institute of Technology, No.5,

Zhongguancun South Street, Haidian District, Beijing 100081, China 2 Faculty of Engineering, Kagawa University, 2217-20 Hayashi-cho, Takamatsu, Kagawa 760-8521, Japan E-Mails:

{zhouwei & guoshuxiang &chenzhengyang} @bit.edu.cn; * Corresponding author

Abstract - Based on the recent research, the force feedback equipment with non-contact displacement measure device is helpful and valuable, which can reduce the size and increase flexibility of master manipulator largely, and so on. In this paper, a novel axil force feedback device with non-contact displacement measure equipment is designed. Firstly, the design theory based on electromagnetics and the working principle are elaborated in detail. Secondly, the calibration experiment of non-contact displacement measure equipment is done, which is used to build the relationship between the displacement and the pixel values. Lastly, Motion interference of moving parts are analyzed simply, and the experiments are done to verify the performance of displacement measurement. By analyzing the experimental results, this axial force feedback device is helpful and valuable for miniaturization of the master manipulator. Index Terms - Vascular interventional surgery, Master manipulator, Axial force feedback device, Non-contact displacement measurement.

I. INTRODUCTION

Cardio-cerebrovascular diseases are characterized by high disability rate and high mortality rate, which seriously threaten human health [1]-[4]. And the vascular interventional surgery (VIS) is the main method to diagnose and treatment these diseases. With the development of automatic control technology, the surgical robot applied to this area is widely studied in many companies and universities. And this kind of surgical robot mainly takes advantage of master-slave mode, it consists of three parts: master manipulator, slave manipulator and the communication system of them. And the master-slave system has these advantages, such as: lower X-radiation, being good to the surgeon’s health. Some robotic system has achieved commercialized, such as: Corpath GRX system developed by Corindus company, Amigo system developed by Catheter Robotic company and so on [5]. A novel slave robot was developed, and the theory and method of cooperative operation of guide wire and catheter are put forward, at the same time, the measurement and compensation method of force during operation were also put forward, which largely improved precision of operation, and the effectiveness of the salve robot is verified by clinical trial [6]-[9]. Because the master manipulator is operated in one safe space without X-radiation, the surgeon will not wear 20Kg lead protective clothes, so the master-slave robotic system for VIS is helpful to protect the

surgeon. Meanwhile, how to provide the feeling of operation from slave to master and the method of displacement measurement are the key issues, and the feeling can also improve the surgical accuracy, which show that the research on the method of force feedback for master manipulator is very important and valuable. Force feedback device is one part of master manipulator, and when this device receive the force signal generated by the contact between the guidewire or catheter with the vascular, the device will generate force to the hands of surgeon, then the surgeon will adjust the operational action according to the feedback force. A kind of master-slave robotic system with force feedback was developed, and magnetorheological fluid (MRF) is used to provide the axil force feedback, but this method can only provide smaller force, and the stability of the device with a bigger volume is a little poorer, at the same, although the displacement is measured by optical mouse sensor, the force feedback device is separated with the sensor, which also increases the size of manipulator largely [10]-[15]. A low-cost tactile robotic sleeve for autonomous endoscopes and catheters, and it has the ability to sense vibration, stretch and pressure on opposing sides of the endoscope can render crucial tactile feedback to achieve autonomous operation in narrow channels, such as cardiovascular track [16]. A novel master manipulator with force feedback based on the principle of electromagnetic force was developed [17]. A vascular international vascular robot with fuzzy control and force feedback was proposed, which is achieved by Geomagic Touch X (3D Systems Corp, Rock Hill, SC, USA) [18]. The research on detection for operation skills and operating force used machine learning, Non-interference operation detection and online detection were done to improve the efficiency of the master-slave endovascular surgery robotic system [19]-[25]. The research on safety and training system based on the virtual reality (VR) were presented to improve the surgical operating skills [26]-[29]. A novel robotic mechanism was proposed, which can achieve translation of the balloon [30]. Magnetic micro active-guidewire was designed and evaluation, which is helpful to navigation and surgical safety [31]. Most of the displacement measurements of the master manipulator is made by grating encoder or motor and so on, which all take advantages of contact method to measure displacement.

In this paper, a novel axil force feedback device is proposed based on the principle of electromagnetics. And the most distinctive contribution is that the non-contact displacement measurement equipment is integrated into the proposed force feedback device, which can further reduce the size and improve the flexibility of the master manipulator. The remaining of this paper are organized as follows: In section II, design theory and working principle of axial force feedback device are shown in detailed. In section III, the calibration experiment of non-contact displacement measure equipment is done. In section IV, experiments and results. In section V, conclusions are presented.

II. DESIGN AND WORKING PRINCIPLE OF AXIAL FORCE FEEDBACK DEVICE

A. Workflow of the Master-Slave Robotic System

In this part, the workflow of the master-slave robotic systems in VIS is showed in Fig. 1. And this system consists of three parts: master manipulator, slave manipulator, and the communication between of them. In this system, the surgeon will operate the master manipulator with the force feedback and displacement measurement device, and the displacement measure is transferred to the slave manipulator, then slave manipulator will operate the surgical instruments. Meanwhile, the operating force of the slave manipulator will be transferred to the force feedback device through current signal, which will provide the feeling to the surgeon. And in Fig. 1 the Feedback Force > 0 is referred to the absolute value of the force is greater than 0.

B. Design of the Axial Force Feedback Device The principle of electromagnetics is applied in many areas, such as: the developed of armamentarium, industrial equipment, aviation field and so on. And the research and application of it are growing up quickly. In the development of the axial force feedback device, the basic theory, which is heterogeneous poles attracting each other, is applied. And the structure diagram of the theory is presented in Fig. 2. In details, the magnetic field intensity of the electromagnet is controlled by current signal, which is generated based on the axial force from the slave manipulator. And the axial force is bigger, the current signal is stronger and more obvious. In the design of this axial force feedback, one permanent magnet and one electromagnet are included. When the magnetic field intensity of the electromagnet is increasing, the distance between the permanent magnet and electromagnet is reducing, which is used to drive the motion of the axial force feedback. And the Maxwell formula are used to compute the force generated by the electromagnet, and the details are shown as follows:

𝐹 = # !"###

$$∗ 𝑆 ∗ %

%&'! (1)

where, the B is the Magnetic flux intensity of magnetic field; S is referred to the surface area; 𝑎 is the modified coefficient, and the value is 3 ~ 5; 𝛿 is Air gap length; and the method of calculation for B is shown in formula (2):

𝐵 = ∅$ (2)

where, ∅ is magnetic flux, which is calculated by the formula (3):

∅ = 𝐼 ∗ 𝑊 ∗ 𝐺 (3)

where, the 𝐼 is the current through the electromagnet; W is the number of coil turns; G is the permeance, which is calculated by the formula (4):

𝐺 = &'∗$

(4) which is a physical quantity to measure the magnetic conductivity of an object, and where the 𝑙 is the length of magnetic circuit; 𝜇 is magnetic permeability; And the meaning and the relationship of the 𝑆, 𝑙, ∅ is shown in Fig. 3. And the direction of the ∅ is along with the 𝑙,and is perpendicular to the S surface.

Fig. 1 The workflow of the Master-slave Robotic System

Fig. 2 The structure diagram of the Principle of Electromagnetics

Fig. 3 The meaning and relationship of parameters

(a) The assembled 3D model of the proposed device.

(b) The details for cross section of the assembled 3D model.

Fig. 4 The whole structure of the axial force feedback device.

C. Structure of the Axial Force Feedback Device Based on the analysis of the design theory, the whole 3D

structure of the axial force feedback device is designed, as shown in Fig. 4. This device has the characteristics of small size, light weight, simple structure and easy installation. Fig. 4 (a) is the assembled 3D model of proposed device, Fig. 4 (b) is The details for cross section of the assembled 3D model, which includes: Box, case cover, spring, permanent magnet, electromagnet, displacement optical sensor, displacement optical sensor supporting frame, permanent magnet supporting frame, drive shaft, photosensitive rubber supporting frame and so on. And the steel material, which can avoid electromagnetic interference phenomenon, is used to manufacture the box and case cover. The spring has the character of compression, which can provide the counter-resistance when the force signal is disappeared and make the permanent magnet and its supporting frame move along the opposite direction of gravity. About the materials of permanent magnet supporting frame, drive shaft,

photosensitive rubber support frame, displacement optical sensor supporting frame and other assembly parts, they are all used the polymer plastics. The special one of this axial force feedback is not only it can provide the force feedback to the surgeon, but also it can measure the moving displacement of the operation which is measured by the displacement optical sensor that is similar with the photoelectric mouse displacement detection device. This kind of sensor can measure the displacements of both X and Y directions at the same time.

D. The Working Principle of Axial Force Feedback Device The design theory and structure of axial force feedback device is introduced above in details. Next, how to work of the axial force feedback device is the main content to present in this part, as shown in Fig. 4 (b). At the beginning, it should be noted that the axial force feedback is achieved by friction force between the photosensitive rubber and the sleeve that is rigidly attached to the catheter or guidewire used in VIS. When the force signal is transferred to the master manipulator from slave manipulator, then the electromagnet will be activated and generate the electromagnetic field. Based on the preset direction of the electromagnetic field, which is opposite to the permanent magnet, the electromagnet will attract the permanent magnet. Then the permanent magnet and its supporting frame will move along the direction of gravity. At the same time, the four springs will be compressed, and the photosensitive rubber and its supporting frame will be closer and closer to the sleeve, so the friction force between them are bigger and bigger. In contrast, when the force signal disappeared, the springs will rebound even to the initial position and the friction will also disappeared at the same time. Meanwhile, unless the feedback force is too large to prevent the catheter or guidewire from moving, they are moving throughout the whole operation that the pressure is applied or released. In addition, the displacement optical sensor will record the displacement data while the catheter or guidewire are moving. As we all known, the displacement data is the order from master manipulator to slave manipulator in the master-slave robotic system, then the slave manipulator will follow the order to complete the surgical operation.

III. CALIBRATION EXPERIMENT OF NON-CONTACT DISPLACEMENT MEASURE EQUIPMENT

In this part, the calibration experiments of non-contact displacement measure equipment are used to build the relationship between the pixel value with the displacement, which includes both X and Y directions. Firstly, optical mouse single chip sensor (PAW3515Db-TJZA, PixArt Imaging Inc.) is selected to detect the displacement change. Secondly, some experiments in different distances are done to record the pixel values and its displacement, and by analyzing the data, the relationship of the them are calculated.

A. Introduction of the Sensor

PAW3515DB-TJZA is an extremely low-cost optical mouse single-chip sensor using CMOS processes, configured with USB interfaces and non-mechanical tracking engines for cursor control of computer mouse. And this sensor is embedded

internal oscillation, so it is convenient and simple. And the main parameters of this sensor are shown in Table I.

A. Calibration Experiments

In order to build the relationship between the pixel value with the distance, some calibration experiments are done, and the corresponding data are recorded in this section. And the 30mm, 50mm, 100mm are included. At the same time, five measurements are included in every distance. Then the details of the measurement results are shown in Fig. 5. And the relationship is calculated, which is formula (5).

The relationship of the pixel value and distance is:

𝑌 = 36.11 ∗ 𝑋 − 56.472 (5)

where, the 𝑋 represents the distance; the 𝑌 represents the pixel value.

IV. EXPERIMENTS AND RESULTS

In this paper, a novel axial force feedback device with non-contact displacement measure equipment is manufactured, and the detailed is shown in Fig. 6. Firstly, the analysis of motion interference of moving parts is presented. Secondly, the non-contact displacement measurement experiments are done to verify the efficiency of the axil force feedback device.

A. Manufacture of the Devices About the structure of the device, the real structure is the

same with the proposed model in Part II. In the real model of the device, the Box, case cover, displacement optical sensor supporting frame, permanent magnet supporting frame, drive shaft, photosensitive rubber supporting frame and other assembly parts are manufactured by 3D printer (iSLA660, ZRapid Tech), and the layer thickness, printing materials and printing time are 0.1mm, photosensitive resin and 195 minutes respectively, which is low cost and convenient.

B. Analysis of Motion Interference In this part, the main work is to show the results of the

motion interference for moving part of the device. And the analysis is presented through the kinematic simulation by software Creo 2.0 and the manual movement of the real structure. And the results show that there is no motion interference of all moving parts.

C. Evaluation of the Displacement Measurement Device

In this part, some experiments are conducted to verify the performance of the non-contact displacement measurement. According to the operational stroke of master manipulator in tele-operation in VIS, the following distance are included, which is the 20mm, 50mm, 100mm, 150mm and 200mm. And the deviation results are shown in Fig. 7. By analyzing the results, the maximum deviation is 1.84mm with the stroke of 200mm, and the minimum deviation is 0.09mm with the stroke of 20mm, the mean deviation is 0.724mm, which shows that the accuracy of the non-contact displacement measurement device is high, which this method is very effective.

TABLE I MAIN SPECIFICATIONS OF SENSOR

Power 4.25V~5.5V

Interface USB

Most speed 30 inches/sec

Resolution 1000

Frame Rate 3300 frame/sec

Working current 10 mA @ Normal state

5 mA @ Stopping state

Encapsulation type

Mis-column double row S-DIP8

Fig. 5 The results of the calibration experiments

Fig. 6 The axial force feedback device

Fig. 7 The deviation of different displacement

V. CONCLUSIONS

In this paper, the axial force feedback device with non-contact displacement measurement sensor is designed, which can provide the functions of force feedback and displacement measurement at the same time. This is the most special of this device proposed in this paper. By analyzing the motion interference and the results of the experiments for the non-contact measurement sensor, the efficiency and high accuracy of this sensor is verified, which is helpful for the miniaturization of the master manipulator for VIS.

But there are more works to be done, including the verification of the force feedback, and the development of control system and so on. In the future work, the performance experiments of this axial force feedback device will also be verified in EVE model or clinical by the surgeon.

ACKNOWLEDGMENT

This research is partly supposed by National High-tech R&D Program (863 Program) of China (No.2015AA043202).

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