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Abstract— This research aims to create a medical drilling device where surgeons can receive the signal and data on the computer screen. We analyze the current signal extract from hall effect-based linear current sensor using a Raspberry Pi engineer board to detect the breakthrough signal.

I. INTRODUCTION

In modern orthopedic surgery, various surgical interventions are being applied such as drilling, reaming and sawing, all of which are very common. Specifically, our work focuses on bone-drilling procedures [1] [2] [3].

Bone drilling procedures are performed in very unusual surgical specialties, for example, orthopedic surgery, ear surgery, maxillofacial surgery, and neurosurgery. Osteosynthesis normally requires multiple bone-drilling operations. In many cases, this operation is extremely accurate. It requires high precision and accuracy in order to drill only to the required depth. Even the slightest deviation in the drilling path can damage the tissue surrounding the bone. Like veins, arteries, spinal cord, brain tissue, etc. Those are very fragile part of our body and causing irreversible damage to the patient, even worse, damage to a patient’s life.

The main disadvantage of innovative drilling tools is that there is no way to identify when the hole has been made or the desired depth is reached. Moreover, a breakthrough can push the drill bit further along the drilling axis due to the inertia of the drilling force. Currently, the efficacy of the drilling procedure depends on the experience and intuition of the surgeon.

Thus, researchers [4] [5] use intelligent control that can assist the surgeon. Pressure sensors are utilized to receive the force and torque. When the drill penetrates the bone, it can receive the biggest force and torque. Then the drill will stop immediately after the penetration. The other significant issue is the accuracy of the path [6] [7].

Because of the variation of the bone thickness and density, also difference in shaping in each part, choosing the proper control of drilling torque and detection of bone breakthrough is quite difficult, but indeed essential. The construction of a drilling system which stops immediately when the drill is breaking through exhibits several difficulties. Therefore, a precise and reliable breakthrough detection method requires

* Corresponding author: Min-Laing Wang is with Asian Institute of

TeleSurgery, Lukang, Taiwan. e-mail: pml.wang@gmail.com * Resrach supported in part by Dept. of Electric Eng. and Advanced Institute

of Manufacturing with High-tech Innovations (AIM-HI), National Chung Cheng Universty, Chia-Yi, Taiwan and Chang Bing Show Chwan Memorial Hospital

taking as numerous useful signals into consideration as possible.

To avoid injuries during surgery, we designed a handheld medical drilling device with electronic force control intended to be utilized to pass through bones. The device is designed in the approach that the surgeon receives an acoustic warning signal as soon as a limiting force has been reached. As an additional feature, we are going to implement a breakthrough detection device to reduce the reaction time of the operator and in this way to reduce the risk of tissue damage of the zone behind the barn. Thus, the plan is to utilize digital servo motors, subtle actuators and force sensors. Those devices have become customary parts in the field of mobile robotics and have proven to be highly reliable. Finally, the micro-controller can receive the signal and send the current to control the drill.

In the first part, several previous researches of the medical drill are reviewed. The direction of what kind of the drill is needed is decided. The second part introduces about how the medical drill is designed and the preparation for the experiments. In the future, the drill that can stop when it penetrates through the bone and retracts for safety consideration will be hoped.

II. SYSTEM DESIGN

A. Circuit Design

A typical bone structure is constituted of a dense outer layer (the cortical bone), and a less dense inner portion (the medullary cavity). Depending on the surgical procedure, the bone drilling process can be separated into two procedures. One is to drill into two cortical walls (from one side of the bone to the other) or only into one cortical wall (without necessarily passing through the medullary cavity). Fig. 1 shows the typical bone structure.

In general, the method for detecting bone layer transition

while drilling is based on the penetration force and cutting torque measured by sensors attached to the drilling tool for

A Drill Signal Detection Technology for Handheld Medical Drilling Device

Michael Mayer1, Hsin-Hung Lin1, Ying-Hua Peng2, Pei Yuan Lee2, Min-Liang Wang*

Figure 1. It is the schematic diagram of bone.

2014 International Symposium on Computer, Consumer and Control

978-1-4799-5277-9/14 $31.00 © 2014 IEEE

DOI 10.1109/IS3C.2014.251

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example force/torque sensors. The concept of this "drill stop" controller is to detect the changes of the force/torque to know the exact moment in time when drill head pass over the bone.

Brett et al. [8] provide an automated drilling methodology to detect the moment of the drill bit's complete breakthrough by identifying a persistent increase of the cutting torque with a persistent decrease of the penetration force simultaneously.

While the drill is rotating, the load on the motor depends on the material which is being drilled in that moment. Since the voltage is constant, the current will be positively correlated with the load. And the load will be positively the cutting torque. Thus, the hardness of the material be estimated by obtaining the changes of current. Moreover, the changes of the material hardness can also be detected by the current if the force applied to the drill remains constant. In this way can be known the relative position of the bone and drill bit. Since the power supply of the drill is a direct current, the current transformer (CT) cannot be used to detect the current. The solution uses a Hall Effect-Based Linear Current Sensor IC to convert the current signal into a voltage signal. Moreover, the voltage is an analog signal, so the analog to digital converter has been utilized to transfer the voltage into digital information.

Based on calculation and experiment, the output voltage of Hall Effect-Based Linear Current Sensor IC only makes a slight difference between the full load and the idle state. To improve the accuracy and make the signal more usable, a proper differential amplifier is being applied to magnify the output from Hall Effect-Based Linear Current Sensor IC.

In order to preserve the flexibility of the circuit, the circuit is combined with a Raspberry Pi engineer board, the I2C interface to communicate between them. The I2C interface is a sequential interface that can connect multiple devices by using only two I/O pins. The interface can load the information from the analog to digital converter into Raspberry Pi. It allows us to combine the signal with sensors, for instance a laser rangefinder.

The motor control interface uses a conventional H-bridge motor controller IC, where the H-bridge controller IC can be driven from the gate-level current. It can be controlled by the general purpose input and output (GPIO) in raspberry Pi without external chips. Furthermore, it can also utilize PWM to control the rotation speed of the drill motor. Despite ones can achieve a PWM signal by utilizing a GPIO pin of the Raspberry Pi directly, due to the electric characteristic of the DC motor, the PWM switching frequency must be above 100HZ. If we apply PWM by utilizing the Raspberry Pi, the CPU loading remains too high to maintain responsiveness of the system. We utilized a PWM controller IC to separate the workload from the CPU. Thus, the torque can be adjusted by changing the PWM duty ratio without affecting the system.

B. Mechanical Design

Fig. 3 is the photo of GrandTek’s handheld medical electric drill and Fig. 4 is the battery of the drill. It is utilized in the experiments.

Figure 3. GrandTek’s handheld medical electric drill.

Figure 2. This is the first drill circuit which can oprate normally.

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Fig. 5 depicts the graphical user interface (GUI) of the

software. The software can receive data from the circuit and show this data on the computer screen. The program is designed to run on a raspberry Pi board. Thus it can be used very easily, and modified if additional functions are needed. Fig. 6 shows all components of the control system prototype.

Human bones differ in various ways. With variable thickness, density or shape, one cannot detect the breakthrough point and control the drill easily. Our system is based on current detection. Since the signal comes from the current

measurement, noise is infeasible. To remove the signal noise and make the signal more accurate to lower the possibility of the miss judgment of breaking through signal, a low pass filter is being applied to our control algorithm.

The concept of Ong and Bouazza-Marouf method, based on a modified Kalman filter was able to establish a trend by smoothing any sudden change in the input signal. The algorithm modified for achieving faster response also smoothing the signal. And first-order minimal pass recursive filter is used. The sum of the coefficients for y[n-1] and x[n] must be less than unity to ensure this low-pass filter remains unity.

III. EXPERIMENT AND RESULT

Fig. 7 shows how the current changes when the drill

contacts a hard surface. At this moment, the voltage increases immediately. If the drill passes through the soft tissue, the voltage decreases or sometimes even vanishes.

A. Problems and Solutions � Still the accuracy of the measurement needs to be

strengthened further. For this purpose, it is planned to deploy superior quality components. For example, one would expect zero voltage at the Hall component at the moment when the drill stops, currently we measure six volts. This problem can be solved by using another Hall component.

� The system reaction time is still longer than 150 milliseconds because of the efficiency of the Raspberry Pi Board. In other words, if the software draws every time after it sampling, the reaction time will be less than 7 Hertz. The solution is to make the software draw once after it sampling 10 times. Efficiency can elevate four times better and the reaction time can down to 40 milliseconds.

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Figure 6. It is the control circuit..

Figure 4. Battery of GrandTek’s handheld medical electric drill.

Figure 5. The GUI of the drill system.

Figure 7. When the drill encounter obstacles, the value will increase

with the voltage (V) immediately.

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� The circuit is designed in that way the drill can rotate in both directions, but currently that fails. That is due to a design error of the circuit. The plan is to redesign the circuit to meet this function, and make the layout of the circuit more space efficient. Fig. 7 depicts the improved circuit which operates normally.

B. Result The voltage will increase when the drill encounters obstacles and decrease when it does not have any resistance. If higher forces are applicable to the drill, the load increase results in a higher voltage. When the forces reduce, the reading decreases. This situation is matching our theory.

IV. CONCLUSION The result shows that the circuit can detect the current. The

current can be turned it into a voltage signal by using Hall component. When the drill encounters obstacles, this current can be observed. On the other hand, the reading will go down when the drill has no resistance. The next step is tantamount to upgrade the safety device and add more functions into the drill, for example detecting the depth. Also adds some outer structure to measure the force applied to the drill by the surgeon. The system is not complete yet, and the way to design a seamless drill is still very long.

ACKNOWLEDGMENT All of us are very thankful for the support of Chang Bing

Show Chwan Memorial Hospital and the Advanced Institute of Manufacturing with High-tech Innovations (AIM-HI) in National Chung Cheng University.

REFERENCES [1] D. Baker, P. Brett, M. Gri�ths, and L. Reyes, “Surgical requirements

for the stapedotomy tool: data and safety considerations,” in Engineering in Medicine and Biology Society, 1996. Bridging Disciplines for Biomedicine. Proceedings of the 18th Annual International Conference of the IEEE, vol. 1, pp. 214–215, 1996.

[2] H. Watanabe, K. Kanou, Y. Kobayashi, and M. Fujie, “Development of a steerable drill for acl reconstruction to create the arbitrary trajectory of a bone tunnel,” in Intelligent Robots and Systems (IROS), 2011 IEEE/RSJ International Conference on, pp. 955–960, 2011.

[3] T. Cao, X. Li, Z. Gao, G. Feng, and P. Shen, “An intelligent monitor system of otologic drill to prevent drill bit entangling with the cotton,” in Information and Automation (ICIA), 2010 IEEE International Conference on, pp. 13–17, 2010.

[4] Louredo, Marcos, Inaki Diaz, and Jorge Juan Gil. "A robotic bone drilling methodology based on position measurements." Biomedical Robotics and Biomechatronics (BioRob), 2012 4th IEEE RAS & EMBS International Conference on. IEEE, 2012.

[5] Wen-Yo Lee, Ching-Long Shih, “Control and breakthrough detection of a three-axis robotic bone drilling system.” Mechatronics 16.2 (2006): 73-84.

[6] Jin, Haiyang, et al. "Intraoperative state recognition of a bone-drilling system with image-force fusion." Multisensor Fusion and Integration for Intelligent Systems (MFI), 2012 IEEE Conference on. IEEE, 2012.

[7] P.N. Brett, D.A. Baker, L. Reyes, J. Blanshard An automatic technique for micro-drilling a stapedotomy in the flexible stapes footplate Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine, 209 (4) (1995), pp. 255–262

[8] F.R. Ong, K. Bouazza-Marouf Drilling of bone: a robust automatic method for the detection of drill bit break-through Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine, 212 (3) (1998), pp. 209–221

[9] Iñaki Díaz, Jorge Juan Gil , Marcos Louredo Computer Methods and Programs in Biomedicine Volume 112, Issue 2, Pages 284-292 (2013)

Figure 8. It is the modified circuit which solves the problem mentioned.

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