Electromagnetic torsional micromirror system with closed-loop drive circuit

Abstract

The invention discloses an electromagnetic torsion micro-mirror system with a closed-loop drive circuit, the electromagnetic torsion micro-mirror system is composed of a micro-mirror plate, a piezoresistive sensor, a piezoresistive interface circuit and a phase-locked loop circuit, the phase-locked loop circuit inputs a sine excitation signal to the micro-mirror plate at the initial time, the micro-mirror plate turns around a torsion beam under the influence of Lorentz force under impulse, and the micro-mirror plate rotates around the torsion beam. The resistance value of a piezoresistive sensor bridge at the tail end of the torsion beam can be changed by deformation of the torsion beam, sine wave electric signals carrying frequency information are generated and output, and the electric signals are converted into same-frequency square wave signals through a piezoresistive interface circuit. And the phase-locked loop circuit tracks the frequency difference and the phase difference between the output of the piezoresistive interface circuit and the output of the voltage-controlled oscillator, and adjusts the sine excitation signal output by the phase-locked loop circuit until the inherent frequency signal of the system is stably output, so that the closed-loop driving of the electromagnetic resonant torsion micromirror is realized. The closed-loop driven tracking function enables the micromirror to work in a resonance state all the time, and the method is simple to operate, convenient to design and high in engineering application value.

Description

Technical Field

[0001] The present invention relates to the field of micromirror scanning technology, and in particular to an electromagnetic torsion micromirror system with a closed-loop driving circuit. Background Art

[0002] As a light detection system, LiDAR (Light Detection and Ranging) can achieve high-resolution and high-precision distance measurement and speed measurement and accurate object sensing. Compared with mature radio detection, LiDAR uses light waves shorter than the radio wavelength range for detection and has higher accuracy in 3D sensing. At the same time, LiDAR has the advantages of long detection distance, good coherence, and high spatiotemporal resolution. Therefore, it is widely used in robotics, autonomous driving, security, and environmental monitoring.

[0003] Solid-state LiDAR based on MEMS micromirrors replaces the mechanical scanning structure, realizes compact and lightweight design, and makes the system more integrated. And because MEMS micromirrors have advantages such as light weight, small size, low power consumption and good reliability, MEMS-based LiDAR has broad research prospects. Large mirrors, high scanning frequencies and large torsion angles are important research directions for MEMS micromirrors.

[0004] MEMS micromirrors can control the deflection and reflection of laser beams, play an important role in laser scanning, laser imaging and laser radar, and are important components of solid-state laser radar. MEMS micromirrors have three motion modes: vertical, horizontal and torsion, and can adjust the laser beam through different motion modes. In LiDAR applications, the torsion resonant micromirror can achieve high-speed and large-field scanning by reflecting the laser beam at high speed, improving the natural frequency and torsion angle of the micromirror to optimize the performance of the laser radar. According to different driving principles, micromirrors are divided into electrothermal micromirrors, piezoelectric micromirrors, electrostatic micromirrors and electromagnetic micromirrors. At present, most micromirror driving methods are open-loop driving. The resonant frequency of the micromirror system is calibrated in advance, and the electrical signal of the same frequency is input to drive the micromirror to work at the resonant frequency to increase the reversal angle. Summary of the invention

[0005] The present invention provides an electromagnetic torsion micromirror system with a closed-loop driving circuit, which can ensure the resonance of the micromirror, obtain a larger reversal angle and a faster response speed, and can automatically track the resonant frequency of the micromirror. When the resonant frequency of the micromirror shifts due to environmental or fatigue problems, the closed-loop driving system can track the resonant frequency in real time to maximize the output angle of the micromirror.

[0006] The embodiment of the present invention provides an electromagnetic torsion micromirror system with a closed-loop driving circuit, comprising: a micromirror plate, a piezoresistive sensor, a piezoresistive interface circuit and a phase-locked loop circuit;

[0007] The input end of the micromirror plate is connected to the output end of the phase-locked loop circuit, and the micromirror plate is affected by the Lorentz force under the impulse of the sinusoidal excitation signal output by the phase-locked loop circuit to generate oscillation, so that the micromirror plate flips around the torsion beam;

[0008] The input end of the piezoresistive sensor is connected to the end of the torsion beam of the micromirror plate, and the resistance value of the bridge in the piezoresistive sensor is changed by the deformation of the torsion beam after flipping, so that the piezoresistive sensor outputs a sinusoidal wave electrical signal carrying frequency information;

[0009] The input end of the piezoresistive interface circuit is connected to the output end of the piezoresistive sensor, and is used to amplify the sinusoidal wave electrical signal of the piezoresistive sensor and convert it into a square wave signal of the same frequency;

[0010] The input end of the phase-locked loop circuit is connected to the output end of the piezoresistive interface circuit, and is used to receive the same-frequency square wave signal, and track the frequency difference and phase difference between the same-frequency square wave signal and the sinusoidal excitation signal, and adjust the sinusoidal excitation signal output by the phase-locked loop circuit to the micromirror mirror plate according to the frequency difference and phase difference, until the phase-locked loop circuit outputs a driving signal of the system's natural frequency, thereby realizing the closed-loop driving function.

[0011] Optionally, in one embodiment of the present invention, the micromirror plate is composed of an octagonal mirror plate, a double-ended torsion beam, a double-turn copper coil and a gold thin film mirror; the octagonal mirror plate is supported by the double-ended torsion beam, the octagonal gold thin film mirror is attached to the center of the octagonal mirror plate, the double-turn copper coil is on the edge of the octagonal mirror plate and connected to the outer frame via the right torsion beam, and the sinusoidal excitation signal output by the phase-locked loop circuit is applied to the double-turn copper coil.

[0012] Optionally, in one embodiment of the present invention, the piezoresistive sensor is a P-type doped silicon resistor with a square structure, which is integrated at the end of the torsion beam on the left side of the micromirror plate, and leads are connected to the four corners of the square to form a Wheatstone bridge structure, one pair of lead-out wires serves as a power supply end, and the other pair of lead-out wires serves as an output end connected to the piezoresistive interface circuit.

[0013] Optionally, in one embodiment of the present invention, the piezoresistive interface circuit is composed of a first low-pass filter, a zero-crossing comparator and a waveform converter;

[0014] Among them, the input end of the first low-pass filter is connected to the output end of the piezoresistive sensor, the output end is connected to the input end of the zero-crossing comparator, the output end of the zero-crossing comparator is connected to the input end of the waveform converter, and the output end of the waveform converter is connected to the phase-locked loop circuit.

[0015] Optionally, in one embodiment of the present invention, the phase-locked loop circuit is composed of a phase detector, a second low-pass filter and a voltage-controlled oscillator;

[0016] The input end of the phase detector is respectively connected to the first output end of the voltage-controlled oscillator and the output end of the piezoresistive interface circuit, and the output end is connected to the input end of the second low-pass filter, for tracking the frequency difference and phase difference between the same-frequency square wave signal and the sinusoidal excitation signal;

[0017] The input end of the voltage-controlled oscillator is connected to the output end of the second low-pass filter, and the second output end is connected to the micromirror plate for outputting the sinusoidal excitation signal.

[0018] Optionally, in one embodiment of the present invention, adjusting the sinusoidal excitation signal output by the phase-locked loop circuit to the micromirror plate according to the frequency difference and the phase difference comprises:

[0019] The frequency difference and phase difference are converted into a DC control voltage, the frequency of the sinusoidal excitation signal output in the previous cycle is used as the center frequency, the output frequency of the sinusoidal excitation signal after adjustment in the current cycle is determined, and the adjusted sinusoidal excitation signal is output to the micromirror plate.

[0020] The closed-loop driving function of the electromagnetic torsion micromirror system with a closed-loop driving circuit in the embodiment of the present invention can automatically track the resonant frequency, ensure that the input signal can make the micromirror system work in a resonant state, have a high quality factor Q value, and a large micromirror torsion angle. The present invention is easy to use and simple to operate. There is a slight difference in the natural frequency of the system, and the influence of the difference can be avoided, and there is no need to test the natural frequency of the system before work.

[0021] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0023] Figure 1 A schematic diagram of the structure of an electromagnetic torsion micromirror system with a closed-loop driving circuit provided according to an embodiment of the present invention;

[0024] Figure 2 is a schematic structural diagram of a micromirror plate portion of an embodiment of the present invention;

[0025] Figure 3 Schematic diagram of the structure of a piezoresistive sensor according to an embodiment of the present invention. DETAILED DESCRIPTION

[0026] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0027] Figure 1 The present invention is a schematic diagram of the structure of an electromagnetic torsion micromirror system with a closed-loop driving circuit according to an embodiment of the present invention.

[0028] like Figure 1 As shown, the electromagnetic torsion micromirror system with a closed-loop driving circuit includes: a micromirror plate 1, a piezoresistive sensor 2, a piezoresistive interface circuit 3 and a phase-locked loop circuit 4.

[0029] The input end of the micromirror plate 1 is connected to the output end of the phase-locked loop circuit 4. The micromirror plate 1 is affected by the Lorentz force under the impulse of the sinusoidal excitation signal output by the phase-locked loop circuit 4 to generate oscillation, so that the micromirror plate 1 flips around the torsion beam.

[0030] The input end of the piezoresistive sensor 2 is connected to the end of the torsion beam of the micromirror plate 1. The resistance value of the bridge in the piezoresistive sensor 2 is changed by the deformation of the torsion beam after flipping, so that the piezoresistive sensor 2 outputs a sinusoidal electrical signal carrying frequency information;

[0031] The input end of the piezoresistive interface circuit 3 is connected to the output end of the piezoresistive sensor 2, and is used to amplify the sinusoidal wave electrical signal of the piezoresistive sensor 2 and convert it into a square wave signal of the same frequency;

[0032] The input end of the phase-locked loop circuit 4 is connected to the output end of the piezoresistive interface circuit 3, and is used to receive a square wave signal of the same frequency, and track the frequency difference and phase difference between the square wave signal of the same frequency and the sinusoidal excitation signal, and adjust the sinusoidal excitation signal output by the phase-locked loop circuit 4 to the micromirror plate 1 according to the frequency difference and phase difference, until the phase-locked loop circuit 4 outputs a driving signal of the system's natural frequency, thereby realizing the closed-loop driving function.

[0033] like Figure 2 As shown, in one embodiment of the present invention, the micromirror plate 1 is composed of an octagonal mirror plate 1-1, a double-ended torsion beam 1-2, a double-turn copper coil 1-3 and a gold thin film mirror 1-4; the octagonal mirror plate 1-1 is supported by the double-ended torsion beam, the octagonal gold thin film mirror 1-4 is attached to the center of the octagonal mirror plate 1-1, the double-turn copper coil 1-3 is on the edge of the octagonal mirror plate 1-1 and connected to the outer frame via the right torsion beam, and the sinusoidal excitation signal output by the phase-locked loop circuit 4 is applied to the double-turn copper coil 1-3.

[0034] Specifically, when driven by a DC current, the double-turn copper coils on both sides of the edge of the octagonal mirror plate are subjected to an external static magnetic field H ext The action of the mirror plate produces a Lorentz force in the direction perpendicular to the mirror plate, and the uniform force F 1 and F 2 The magnitudes are equal and the directions are opposite, and the torques in the same direction are generated on the mirror plate of the micromirror. The electromagnetic micromirror is subjected to the static Lorentz force and produces torsional motion. The Lorentz forces of different magnitudes cause the micromirror to produce steady-state torsional motions of different angles. The mirror plate is approximately a rigid body during the motion, so the static torsional motion of the micromirror can be equivalent to the static torsion of the torsion beam structure. Under the condition of being subject to approximately double-end fixed constraints, the torsion beam structure is subjected to the torque generated by the motion of the mirror plate and produces torsion. According to the Lorentz force formula, the torque T on the beam is as follows:

[0035] T=BIlr

[0036] Where B is the magnitude of the external magnetic field, I is the magnitude of the current in the coil, l is the effective length of the wire subjected to the Lorentz force, and r is the radius of the mirror plate perpendicular to the beam. The cross section of the torsion beam is designed to be rectangular. According to the torsion theory of rectangular cross-section beams, under the action of static torsion torque, the torsion angle for:

[0037]

[0038] Where L is the length of the micromirror torsion beam, G is the elastic shear modulus of the beam material, and J p is the inertia torque of the rectangular cross-section beam, E is the Young's modulus of the beam material, and ρ is the Poisson's ratio of the beam material. The piezoresistive sensor on the end surface of the beam realizes differential voltage output due to deformation.

[0039] like Figure 3 As shown, in one embodiment of the present invention, the piezoresistive sensor 2 is a P-type doped silicon resistor with a square structure, which is integrated at the end of the torsion beam on the left side of the micromirror plate 1, and leads are led out at the four corners of the square to form a Wheatstone bridge structure, one pair of lead-out wires serves as a power supply end, and the other pair of lead-out wires serves as an output end connected to the piezoresistive interface circuit 3.

[0040] Specifically, the piezoresistive sensor has a Wheatstone bridge structure, and the four doped silicon resistors have the same resistance value and the adjacent resistor strips are perpendicular to each other. The square formed by the piezoresistors of the full bridge is designed to be 45° to the long direction of the torsion beam. The full-bridge silicon piezoresistive sensor is suitable for torque measurement. The sensor is integrated at the end of the micromirror torsion beam to monitor the torsion angle of the micromirror. The torsion of the micromirror causes the torsion beam to torsion, causing the surface of the beam to produce tangential tensile stress T and compressive stress C along the surface of the beam. Among them, the c and d bridges are subjected to compressive stress to produce compressive strain, resulting in a decrease in resistance value, while the a and d bridges are subjected to tensile stress to produce tensile strain, resulting in an increase in resistance value. Under the action of fixed voltage excitation, this change in relative bridge resistance causes a change in the resistance voltage divider and outputs a potential difference V positively correlated with the stress at the output end. OUT .

[0041] V out =V s Gε

[0042] Among them, V S is the driving voltage, G is the gauge coefficient of the piezoresistance, and ε is the strain of the material. The longitudinal stretch and compression of the piezoresistance are equivalent to the shear stress. The output of the piezoresistive sensor with a Wheatstone bridge structure has a linear relationship with the mechanical force, so it is more sensitive to torsional motion.

[0043] like Figure 1 As shown, in one embodiment of the present invention, the piezoresistive interface circuit 3 is composed of a first low-pass filter 3-1, a zero-crossing comparator 3-2 and a waveform converter 3-3. Among them, the input end of the first low-pass filter 3-1 is connected to the output end of the piezoresistive sensor 2, the output end is connected to the input end of the zero-crossing comparator 3-2, the output end of the zero-crossing comparator 3-2 is connected to the input end of the waveform converter 3-3, and the output end of the waveform converter 3-3 is connected to the phase-locked loop circuit 4. The piezoresistive interface circuit 3 removes high-frequency clutter signals, and amplifies the sinusoidal wave electrical signal output by the piezoresistive sensor 2 and converts it into a square wave signal of the same frequency to meet the input requirements of the phase-locked loop circuit 4.

[0044] like Figure 1 As shown, in one embodiment of the present invention, the phase-locked loop circuit 4 is composed of a phase detector 4-1, a second low-pass filter 4-2 and a voltage-controlled oscillator 4-3 (Voltage Controlled Oscillator, VCO).

[0045] The input end of the phase detector 4-1 is connected to the first output end of the voltage-controlled oscillator 4-3 and the output end of the piezoresistive interface circuit 3 respectively, and the output end is connected to the input end of the second low-pass filter 4-2, for tracking the frequency difference and phase difference between the same-frequency square wave signal and the sinusoidal excitation signal;

[0046] The input end of the voltage controlled oscillator 4 - 3 is connected to the output end of the second low-pass filter 4 - 2 , and the second output end is connected to the micromirror plate 1 for outputting a sinusoidal excitation signal.

[0047] Optionally, in one embodiment of the present invention, adjusting the sinusoidal excitation signal output by the phase-locked loop circuit to the micromirror plate according to the frequency difference and the phase difference includes:

[0048] The frequency difference and phase difference are converted into a DC control voltage, the frequency of the sinusoidal excitation signal output in the previous cycle is used as the center frequency, the output frequency of the adjusted sinusoidal excitation signal in the current cycle is determined, and the adjusted sinusoidal excitation signal is output to the micromirror plate.

[0049] In an embodiment of the present invention, the mirror plate is placed in a magnetic field. When the system is working, the voltage-controlled oscillator 4-3 first outputs an initial sinusoidal excitation signal to the double-turn copper coil of the micromirror mirror plate. After the micromirror mirror plate is stimulated, it oscillates under the influence of the Lorentz force. The mirror plate moves around the torsion beam due to the force. The piezoresistive sensor on the surface of the end of the beam generates an AC voltage signal output due to the deformation. The output of the piezoresistive sensor is converted into a square wave signal of the same frequency through the piezoresistive interface circuit. Since there is a certain phase difference and frequency difference between the initial output of the voltage-controlled oscillator and the output of the micromirror system, the phase difference and frequency difference of the signals of different frequencies are captured by the phase detector and the low-pass filter, and the output of the voltage-controlled oscillator is adjusted until the voltage-controlled oscillator is stable and outputs a driving signal of the system's inherent frequency, thereby realizing the function of closed-loop driving.

[0050] When adjusting the output of the voltage-controlled oscillator, the phase detector and low-pass filter capture the phase difference and frequency difference of signals of different frequencies, and convert them into a DC control voltage. The output frequency of the previous cycle is used as the center frequency, and the adjusted output frequency of this cycle is determined and output to the copper coil surrounding the mirror plate to achieve the tracking system's natural frequency and complete the closed-loop drive of the micromirror. When the laser beam is transmitted to the mirror surface of the micromirror, the micromirror driven by the Lorentz force reflects the laser beam in a resonant motion, realizing the function of the micromirror.

[0051] According to the electromagnetic torsion micromirror system with a closed-loop drive circuit proposed in the embodiment of the present invention, it is composed of a micromirror mirror plate, a piezoresistive sensor, a piezoresistive interface circuit and a phase-locked loop circuit. The voltage-controlled oscillator in the phase-locked loop circuit initially inputs a sinusoidal excitation signal to a double-turn copper coil integrated on the micromirror mirror plate. The mirror plate flips around the torsion beam under the influence of the Lorentz force under the impulse. The deformation of the torsion beam changes the resistance value of the piezoresistive sensor bridge at the end of the beam, generating a sinusoidal wave electrical signal output carrying frequency information. After the piezoresistive interface circuit, the electrical signal is converted into a square wave signal of the same frequency. The phase detector of the phase-locked loop circuit tracks the frequency difference and phase difference between the output of the piezoresistive interface circuit and the output of the voltage-controlled oscillator, and adjusts the output of the voltage-controlled oscillator until the natural frequency signal of the output system is stabilized, thereby realizing the closed-loop drive of the electromagnetic resonant torsion micromirror. The tracking function of the closed-loop drive of the present invention enables the micromirror to always work in a resonant state, and is simple to operate, convenient to design, and has good engineering application value.

[0052] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or N embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0053] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "N" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

Claims

1. An electromagnetic torsion micromirror system with a closed-loop drive circuit, characterized in that: include: Micromirror plate, piezoresistive sensor, piezoresistive interface circuit and phase-locked loop circuit; The input end of the micromirror plate is connected to the output end of the phase-locked loop circuit, and the micromirror plate is affected by the Lorentz force under the impulse of the sinusoidal excitation signal output by the phase-locked loop circuit to generate oscillation, so that the micromirror plate flips around the torsion beam; The input end of the piezoresistive sensor is connected to the end of the torsion beam of the micromirror plate, and the resistance value of the bridge in the piezoresistive sensor is changed by the deformation of the torsion beam after flipping, so that the piezoresistive sensor outputs a sinusoidal wave electrical signal carrying frequency information; The input end of the piezoresistive interface circuit is connected to the output end of the piezoresistive sensor, and is used to amplify the sinusoidal wave electrical signal of the piezoresistive sensor and convert it into a square wave signal of the same frequency; The input end of the phase-locked loop circuit is connected to the output end of the piezoresistive interface circuit, and is used to receive the same-frequency square wave signal, and track the frequency difference and phase difference between the same-frequency square wave signal and the sinusoidal excitation signal, and adjust the sinusoidal excitation signal output by the phase-locked loop circuit to the micromirror mirror plate according to the frequency difference and phase difference, until the phase-locked loop circuit outputs a driving signal of the system's natural frequency, thereby realizing the closed-loop driving function.

2. The system according to claim 1, characterized in that The micromirror plate consists of an octagonal mirror plate, a double-ended torsion beam, a double-turn copper coil and a gold film mirror; the octagonal mirror plate is supported by the double-ended torsion beam, the octagonal gold film mirror is attached to the center of the octagonal mirror plate, the double-turn copper coil is on the edge of the octagonal mirror plate and connected to the outer frame via the right torsion beam, and the sinusoidal excitation signal output by the phase-locked loop circuit is applied to the double-turn copper coil.

3. The system according to claim 1, characterized in that The piezoresistive sensor is a P-type doped silicon resistor with a square structure, which is integrated at the end of the torsion beam on the left side of the micromirror plate, and leads are connected to the four corners of the square to form a Wheatstone bridge structure. One pair of lead wires serves as a power supply end, and the other pair of lead wires serves as an output end connected to the piezoresistive interface circuit.

4. The system according to claim 1, characterized in that The piezoresistive interface circuit is composed of a first low-pass filter, a zero-crossing comparator and a waveform converter; Among them, the input end of the first low-pass filter is connected to the output end of the piezoresistive sensor, the output end is connected to the input end of the zero-crossing comparator, the output end of the zero-crossing comparator is connected to the input end of the waveform converter, and the output end of the waveform converter is connected to the phase-locked loop circuit.

5. The system according to claim 1, characterized in that The phase-locked loop circuit is composed of a phase detector, a second low-pass filter and a voltage-controlled oscillator; The input end of the phase detector is respectively connected to the first output end of the voltage-controlled oscillator and the output end of the piezoresistive interface circuit, and the output end is connected to the input end of the second low-pass filter, for tracking the frequency difference and phase difference between the same-frequency square wave signal and the sinusoidal excitation signal; The input end of the voltage-controlled oscillator is connected to the output end of the second low-pass filter, and the second output end is connected to the micromirror plate for outputting the sinusoidal excitation signal.

6. The system according to claim 5, characterized in that The method further comprises: adjusting the sinusoidal excitation signal output by the phase-locked loop circuit to the micromirror plate according to the frequency difference and the phase difference, comprising: The frequency difference and phase difference are converted into a DC control voltage, the frequency of the sinusoidal excitation signal output in the previous cycle is used as the center frequency, the output frequency of the sinusoidal excitation signal after adjustment in the current cycle is determined, and the adjusted sinusoidal excitation signal is output to the micromirror plate.

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