Circular microphone array system and method for bone milling angle and depth monitoring based on milling sound

Abstract

This invention provides a circular microphone array system and method for monitoring bone milling angle and depth based on milling sound, belonging to the technical field of surgical instruments. The system includes a microphone clamp with an even number of microphone component slots. At each end of the microphone clamp is a claw that secures it to a cutting tool. Each microphone component slot can hold one microphone component. Each microphone is connected to a processor via a communication bus. The processor processes the sound signals collected by each microphone and then outputs the changes in depth and angle of the cutting tool relative to the bone surface during milling. This invention can collect sound signals during bone milling in real time and autonomously identify the plane where the milling tilt angle occurs and the optimal sound frequency band that reflects the angle change during sound signal processing. It enables monitoring of angle and depth during bone milling, helping to control orthopedic surgical robots in an ideal bone-cutting state, thereby improving safety during bone milling.

Description

Technical Field

[0001] This invention relates to the technical field of surgical aids, specifically to a circular microphone array system that can utilize the bone-cutting sounds generated during bone milling surgery to monitor the angle and depth of bone milling. Background Technology

[0002] In most orthopedic surgeries, surgeons use high-speed rotating cutting tools to mill bones. The vibration of the cutting tool and the surgeon's fatigue level both affect the milling accuracy. Because milling cutters are mostly spherical, the instantaneous amount of material removed varies depending on the angle at which the cutter is used. For example, in laminectomy to reduce decompression, the surgeon will mill away different thicknesses of the lamina when holding the tool vertically and at an angle with the same force. If the surgeon misjudges the milling angle and depth, there is a high risk of milling through the lamina and damaging nerves or other soft tissues.

[0003] The rapid development of robots has led to their widespread application across various industries, significantly improving work efficiency and safety. To address the aforementioned issues, surgical robots equipped with milling cutters are introduced to assist in surgery. This reduces surgical risks caused by surgeon fatigue, as surgical robots do not experience the tremors or slippage that occur with human hands during bone milling. However, surgical robots cannot predict and select appropriate force and angles based on experience like surgeons. Furthermore, bone surfaces often have varying densities and curvatures, which differ from person to person. This makes it difficult to measure the depth of contact between the milling cutter and the bone surface, as well as the angle of the milling cutter relative to the bone surface, in real time using ordinary sensors (rangefinders, gyroscopes, etc.). This poses significant challenges to controlling the milling depth and angle of the surgical robot.

[0004] Currently, the detection and control of milling angle and depth mainly rely on various sensors, such as force / torque sensors, accelerometers, laser displacement sensors, and microphones. Taking the laser displacement sensor as an example: this sensor can indeed measure the milling depth relatively accurately, and the milling angle of the tool can be measured using two or more sensors. However, this is only limited to relatively flat bone surfaces, and flat bone surfaces are rare in actual surgery. In addition, the advantages of force / torque sensors and accelerometers in measuring milling angles are not obvious. The main advantages of detecting bone milling angle and depth based on sound signals are as follows: (1) microphones are relatively inexpensive; (2) the accuracy requirements for the installation position are low, and it does not depend on specific clamping devices. It is only necessary to attach the microphone matrix to the tool, without changing the robot configuration; (3) sound signals contain a lot of information, and angle and depth information can be obtained using only one sound signal; (4) it has little impact on the surgical process, as it does not emit sound or light, and causes little interference during the surgical process. Summary of the Invention

[0005] This invention addresses the problem of monitoring the milling depth and angle of a milling cutter during orthopedic robotic bone milling surgery. It proposes a circular microphone array capable of monitoring the milling angle and depth using the sound of bone cutting during the procedure. The circular microphone array is externally attached to the surgical blade to collect sound during the operation, and then the sound signals are processed. The milling depth is monitored based on the energy level within the corresponding frequency range of the collected milling sound, and the milling angle is monitored based on the relative differences in the sound signals collected by different microphones.

[0006] The technical solution of the present invention is as follows:

[0007] A circular microphone array system for monitoring bone milling angle and depth based on sound during bone milling is disclosed. The system includes a microphone fixture with N microphone components and tool clamping devices (jaws) at both ends. The microphones on the microphone fixture are connected to a processor via a communication bus. After the microphones collect sound signals, they are transmitted to the processor. The processor performs short-time fast Fourier transform and wavelet transform on the sound signals collected by each microphone to extract the characteristics of the sound signals and compares the characteristics of the sound signals of the corresponding microphones: (1) the change in milling depth is reflected by the change in the characteristics of the corresponding frequency bands of the sound signals; (2) the change in milling angle is reflected by the change in the relative difference between the characteristics of the corresponding frequency bands of the sound signals collected by the corresponding microphones. After calibration in the milling experiment of artificial bone material, the changes in depth and angle during the milling process can be output and used as feedback signals to control the surgical robot to work in an ideal working state.

[0008] The microphone clamp refers to a device designed to hold a microphone and fix itself on a milling cutter. The microphone clamp is a hollow, through-hole truncated cone shape, with N microphone component slots on the microphone clamp. The number of these slots must be even, and the positions of the slots must conform to the principle of central symmetry.

[0009] The aforementioned aligned microphones refer to a pair of microphones, one on the designed microphone fixture and another microphone symmetrical to it. This invention enables non-planar angle monitoring through different aligned microphones. For example, adding only one pair of aligned microphones to the fixture allows for angle monitoring on a single milling plane; adding another pair allows for monitoring the milling angles on two planes.

[0010] The aforementioned tool clamping device refers to a device at one end of the microphone clamp used to fix the entire microphone clamp onto the milling cutter. It consists of three locking teeth with limiting positions, and each locking tooth has a spring behind it to lift the locking tooth, which can easily realize the quick installation and removal of the microphone clamp and the tool.

[0011] The processor is responsible for processing the sound signals collected every n seconds by N microphones on the microphone fixture. It analyzes the sound signals, outputs and monitors the changes in milling depth and angle during the milling process based on the differences in the collected sound characteristics. The method involves first performing a wavelet transform on the collected signals, then subtracting the transformed data from the corresponding microphones to obtain N / 2 data points. A maximum value search is then performed on these N / 2 data points to obtain the set with the largest value. The plane corresponding to this set of data points is the plane where the milling tilt angle occurs. Secondly, assuming the microphone sampling frequency is F, after performing the wavelet transform on the sound signal, the entire frequency band from 0 to F is divided into M parts, and the bandwidth of each part is F / M. Furthermore, S... aij This is the sum of the decibel values ​​obtained by wavelet transform of the j-th frequency band of sound collected by the i-th microphone in group a. For example, the sum of the decibel values ​​obtained by wavelet transform of the 0-F / M frequency band of the first microphone in the first microphone pair of group a is S. 111 The sum of the decibel values ​​obtained from wavelet transform of the 0-F / M band of the second microphone is S. 121 The F / M to 2F / M frequency band of the first microphone in the first microphone pair is labeled S. 112 The sum of the decibel values ​​obtained from wavelet transform of the F / M to 2F / M frequency bands of the second microphone is S. 122 And so on. Using E aj This represents the two values ​​S of the microphone. a1j and Sa2j The result of the subtraction is E. aj The highest frequency band is denoted as f. Then, a short-time fast Fourier transform is performed on the sound signal collected every n seconds, and the amplitudes within the f band are summed and denoted as SUM. Finally, the SUM values ​​of the corresponding microphone are divided and denoted as SUM1. This yields the relative difference in sound characteristics between the two microphones. The change in the value of SUM1 can be used to display the change in milling angle from one n seconds to the next n seconds. Simultaneously, the change in the value of SUM can also reflect the change in milling depth.

[0012] Advantages and positive effects of the present invention:

[0013] This invention enables real-time acquisition of sound signals during bone milling. Only a single wavelet transform is needed to obtain the optimal sound frequency range for reflecting the milling angle, saving screening time. This aligning microphone design overcomes the challenge of monitoring angles during bone milling. Furthermore, it allows simultaneous monitoring of both angle and depth variables using only sound signals. This significantly simplifies the system and reduces its complexity. It reduces the risks associated with improper depth and angle control during orthopedic surgical robots, alleviates surgeon fatigue, and minimizes the risk of adverse consequences, thereby improving safety during bone milling. Attached Figure Description

[0014] Figure 1 This is a system block diagram of one embodiment of the present invention;

[0015] Figure 2 This is a schematic diagram of the chuck claw according to an embodiment of the present invention;

[0016] Figure 3 This is a schematic diagram of a microphone clamp according to an embodiment of the present invention;

[0017] Figure 4 A schematic diagram of a microphone assembly according to an embodiment of the present invention.

[0018] Figure 5 This is an overall schematic diagram of an embodiment of the present invention;

[0019] Figure 6 This is a schematic diagram of parts assembly according to an embodiment of the present invention;

[0020] In the diagram, 1 is the claw housing, 2 is the claw tooth, 3 is the claw limiting tooth, 4 is the microphone component slot, 5 is the claw mounting slot with limiting, 6 is the microphone component mounting slot with limiting, 7 is the microphone transmission line, 8 is the microphone component limiting tooth, 9 is the microphone base, 10 is the microphone, 11 is the microphone component dust cover, and 12 is the spring. Detailed Implementation

[0021] Example 1:

[0022] The circular microphone array system provided in this embodiment, capable of monitoring bone milling angle and depth based on bone milling sounds, is as follows: Figure 1 As shown, the system's grippers, microphone clamps, microphone components, overall system composition, and all system parts are respectively as follows: Figure 2 , 3 As shown in Figures 4, 5, and 6, the system is mounted on a milling cutter and can use a microphone to collect sound signals during bone milling. The data is then transmitted to a processor via a communication bus. The processor analyzes the signals and outputs the changes in the milling angle and depth of the milling cutter relative to the bone surface.

[0023] The system is structured as follows: Figure 5 and Figure 6 As shown, this system includes two jaws and a microphone clamp. The microphone clamp has N microphone component slots 4, each slot 4 housing a microphone component. The number of microphone component slots 4 must be even, and their positions must conform to the principle of central symmetry. Similarly, the installed microphone components must appear in pairs so that two centrally symmetrical microphones 10 within a microphone component form a aligned microphone. As one implementation, in this example, N is 6, and M of the M microphone components is also 6. All microphones are connected to the processor via a communication bus. It should be noted that the number of milling angle planes that the system can determine is related to the number of aligned microphones installed; therefore, the numbers N and M can be any even value other than 6.

[0024] The claw, as Figure 2 As shown, the chuck mainly consists of a chuck housing 1, chuck teeth 2, and a spring 12. The chuck has a two-layer cylindrical nested structure, including a chuck head and a chuck tail. The chuck housing 1 on the outer side of the chuck head has three chuck tooth grooves, and there are three chuck teeth 2 set in the chuck tooth grooves inside. A spring 12 is set behind the chuck teeth 2 to lift the chuck teeth 2, thereby playing a fixing role. The chuck tail has a chuck limiting tooth 3 as a limiting mechanism, which can cooperate with the chuck mounting grooves 5 with limiting at both ends of the microphone clamp to form a whole and fix it on the milling cutter.

[0025] The microphone clamp is as follows Figure 3As shown, the microphone clamp is shaped like a hollow truncated cone, which facilitates the placement and removal of the microphone assembly. Both sides have limiting mechanisms that engage with the jaws. These limiting mechanisms consist of jaw mounting slots 5 with limiting features at both ends of the hollow, through-hole cavity of the microphone clamp, which assemble with the jaws. N microphone assembly slots 4 are distributed on the sides of the microphone clamp and extend through its bottom surface. At the tail of each microphone assembly slot 4, a microphone assembly mounting slot 6 with limiting features is formed for assembling the microphone assembly. The jaws secure the clamp to the milling cutter.

[0026] The microphone assembly is as follows Figure 4 As shown, a microphone assembly consists of a microphone 10, a microphone base 9, and a microphone assembly dust cover 11. The microphone base 9 has a communication data cable connected to the microphone transmission line 7 at the rear, and a microphone pin connector at its head. The microphone 10 connects to the microphone base 9 via these pins. Considering the operating environment of this system, a dust cover is added to the front of each microphone to ensure normal operation. The tail of the microphone base 9 has a microphone assembly limiting tooth 8, which mates with the limiting microphone assembly mounting slot on the microphone clamp.

[0027] This invention describes a method for monitoring the angle and depth of bone milling using a circular microphone array system. The method involves selecting artificial bone material and conducting a bone milling experiment. The artificial bone material is fixed at both ends using pliers. The milling depth is set to 0.4 mm, the lateral movement speed to 1 mm / s, the milling angle to 45 degrees, the milling duration to 10 seconds, and the cutter head speed to 60,000 rpm. The system is attached externally to the milling cutter, with the microphone positioned 10 cm from the cutter head. The microphone sampling frequency is 48,000 Hz, and one microphone pair is used to collect sound signals. An experiment is conducted with a depth of 0.4 mm, a milling angle of 45 degrees, and a lateral movement speed of 1 mm / s. First, the microphone collects the sound for the first 0.5 seconds of the experiment and transmits the sound signal to the processor. The processor performs a wavelet transform on the sound signal. The wavelet transform formula used in this example is: Where 'a' represents the scaling factor controlling the wavelet function's expansion, and 'τ' represents the translation factor controlling the wavelet function's shift, after obtaining the wavelet transform data, the audio signal is divided into frequency bands of 2400 Hz each, with the first band being 0-2400 Hz. The Si value within this band is then calculated. aij The value is S because this experiment only used one microphone pair. aij Let them be S respectively 111 and S 121 Then, based on the S within each segment... aij Value to calculate E aj The value of E obtained aj From a set of data, the data that best reflects the change in angle is E.13 The frequency range corresponding to j=3 is f=4800Hz-7200Hz. After this, the microphone continues to collect sound during the experiment and transmits the sound signal to the processor. The processor performs a short-time fast Fourier transform on the sound signal every 0.5 seconds. The formula for the Fourier transform used in this example is: Where ω represents frequency, after obtaining the Fourier transform data, the amplitudes of the transformed values ​​within the frequency range of f = 4800 Hz to 7200 Hz are summed and denoted as SUM. Then, the SUM from the microphone is divided and denoted as SUM1. Finally, the values ​​of SUM and SUM1 are output. After completing the experiment with a milling angle of 45 degrees, a milling experiment with a milling angle of 90 degrees is performed, with all other experimental conditions remaining the same. Finally, the values ​​of SUM and SUM1 are output. The change in the milling angle can be analyzed by observing the changes in the SUM1 data. In this experiment, the output value SUM1 for a milling angle of 90 degrees remained consistently around 1, while the output value SUM1 for a milling angle of 45 degrees remained consistently around 3. This clearly demonstrates that different milling angles result in different SUM1 values, and the changes in SUM1 effectively reflect the changes in the milling angle. A second set of milling experiments with different depths was then conducted: the milling depth varied uniformly from 0.2 mm to 0.6 mm within 10 seconds, while all other experimental conditions (such as milling angle, traverse speed, and cutter head speed) remained the same. After the microphone captured the sound signal, the processor performed the same calculations and then output the values ​​of SUM and SUM1. The changes in the SUM data reveal the relationship between the milling depth and the overall process.

Claims

1. A circular microphone array system for bone milling angle and depth monitoring based on milling sound, the system is assembled on a milling cutter, characterized in that: The system includes a microphone clamp with N microphone component slots (4), two fixed claws set at both ends of the microphone clamp, and N microphone components. Each microphone component is set in a microphone component slot (4) and connected to the processor through a microphone transmission line (7), where N is an even number. The claws are a two-layer cylindrical nested structure, including a claw head and a claw tail. The claw tail is provided with a claw limiting tooth (3) as a limiting mechanism, which can cooperate with the claw mounting slots (5) with limiting at both ends of the microphone clamp to form a whole and then be fixed on the milling cutter. The microphone assemblies installed on the microphone fixture appear in pairs. The two centrally symmetrical microphones (10) in the microphone assembly are the positioning microphones. The processor first processes and analyzes the sound signals collected by the microphones (10). Based on the differences in the collected sound characteristics, it outputs and monitors the changes in the milling angle and depth of the milling cutter relative to the bone surface during the milling process. The number of milling angle planes that the system can distinguish is related to the number of positioning microphones installed. The microphone clamp is a hollow, through-hole truncated cone shape, with N microphone component slots (4) evenly distributed around its sides. The microphone component slots (4) penetrate the bottom surface of the microphone clamp, and a microphone component mounting slot (6) with a limit is opened at the tail of the microphone component slot (4) for assembling with the microphone component. At both ends of the hollow cavity of the microphone clamp, there are claw mounting slots (5) with a limit for assembling with the claw.

2. The circular microphone array system for monitoring bone milling angle and depth based on milling sound according to claim 1, characterized in that: The claw mainly consists of a claw shell (1), a claw tooth (2), and a spring (12). The claw shell (1) on the outer side of the claw head has three claw tooth grooves, and a claw tooth (2) is provided in the claw tooth groove. There is a limit opening on the inner side of the claw head. A spring (12) is provided at the rear of the three claw teeth (2). The claw teeth (2) are extended by the cooperation of the spring (12) with the claw shell.

3. The circular microphone array system for monitoring bone milling angle and depth based on milling sound according to claim 1, characterized in that: The microphone assembly mainly consists of a microphone (10), a microphone base (9), and a microphone assembly dust cover (11). The head of the microphone base (9) is provided with a microphone pin socket, and a data cable is provided inside to connect the pin to the microphone transmission line (7) at the rear end. The tail of the microphone base (9) is provided with a microphone assembly limiting tooth (8) for cooperating with the microphone assembly mounting slot with limiting on the microphone clamp.

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