Velocity detection of a moving conductor in a magnetic field

Abstract

This invention calculates the velocity of a moving conductor in a magnetic field, emulates this calculation using an operational amplifier, and realizes a velocity signal. This velocity signal can be used as feedback to make the velocity track a system input signal. A dynamic speaker can be conceptualized as a moving conductor in a magnetic field, and this invention provides an effective method for detecting the velocity of the speaker's moving coil.

Description

Technical Field

[0001] (Prior Art) The various aspects discussed in this specification relate to the detection of the velocity of a moving conductor operating in a magnetic field, which is important in motion feedback and control. Specifically, this applies to dynamic speakers that can be conceptualized as moving conductors within a magnetic field. Thus, the discussion regarding the detection of the velocity of a moving conductor in a magnetic field can also be applied to the problem of detecting the velocity of the voice coil of a dynamic speaker.

[0002] The first known patent related to velocity detection can be traced back to British Patent UK272622. This patent proposes a technique for detecting the velocity of a speaker cone using an auxiliary coil. However, in this approach, the effectiveness is hindered by the mutual inductance generated between the auxiliary coil and the voice coil, leading to errors in velocity measurement.

[0003] In another British Patent UK320713, it is proposed to use a capacitor-based approach in detecting the velocity of a speaker cone. Although this method is relatively straightforward, due to the extremely small size of the sensor capacitor, there is a significant obstacle that the noise increases because of the prominent size difference between the environmental capacitor and the sensor capacitor.

[0004] In the most recent approach to velocity detection, an accelerometer is utilized as a sensor attached to the speaker cone to measure and calculate the velocity. For example, in Philips' technology, a piezoelectric accelerometer is used to detect the motion acceleration, and then an integrating circuit is used to calculate the velocity. However, in this approach, several problems arise. Specifically, since there is a non-zero mass in the piezoelectric accelerometer, a time delay occurs in the transmission of velocity to the sensor. Furthermore, there is a possibility of noise generation in the integrating circuit, which impairs the system accuracy.

Background Art

[0005] Accurate velocity detection is essential for controlling the velocity of a moving conductor in a magnetic field. However, existing velocity detection methods are subject to various limitations, making an improved approach to velocity detection of moving conductors in a magnetic field highly desirable. [Overview of the project]

[0006] This invention calculates the velocity of a moving conductor in a magnetic field, emulates this calculation using an operational amplifier, and realizes a velocity signal. This velocity signal can be used as feedback to make the velocity track a system input signal. A dynamic speaker can be conceptualized as a moving conductor in a magnetic field, and this invention provides an effective method for detecting the velocity of the speaker's moving coil. [Brief explanation of the drawing]

[0007] [Figure 1] This is a circuit diagram of an embodiment of speed detection. [Figure 2] This is another circuit diagram of a speed detection embodiment. [Figure 3] The test results using a half-sine wave are shown. [Figure 4] The test results using ramp waves are shown. [Modes for carrying out the invention]

[0008] (Detailed description of the invention) When a voltage is applied to a moving conductor in a magnetic field, the conductor is forced to move. Velocity detection is key in motion feedback and control. If a dynamic speaker can be considered as a moving conductor operating in a magnetic field, then velocity detection of the moving coil becomes crucial for producing high-quality sound.

[0009] When a voltage um is applied to a magnetic field or a moving conductor in a dynamic speaker, the following equation holds: um = R*i + L*di / dt + Kv; where R is resistance, L is inductance, i is current, v is velocity, and K is a constant in a straight magnetic field. To detect velocity v, a detection structure must be constructed.

[0010] The sensing structure is a specially configured component electronically connected to a moving conductor or speaker to derive a mathematical formula for velocity calculation, and the velocity signal can be realized by emulating this formula through an electronic circuit.

[0011] The use of operational amplifiers enables the execution of a wide range of mathematical operations, including addition, subtraction, multiplication, division, differentiation, and integration. After structuring the sensing structure and deriving the formulas for subsequent velocity calculations, it becomes possible to design electronic circuits equipped with operational amplifiers to effectively emulate these formulas and generate velocity signals.

[0012] Figure 1 is a circuit diagram of an embodiment of velocity detection, which includes a moving conductor in a magnetic field 1 connected to a detection structure 2, a derived velocity equation 3, and an operational amplifier 4 equipped with an operational amplifier 4. The voltage across the moving conductor 1 can be expressed as um = R*i + L*di / dt + Kv. In this equation, R is the resistance of the conductor, L is the inductance of the conductor, i is the current, v is the velocity, and K is a constant in a linear system. The detection structure 2 is generated using resistance Ra and inductance La. The voltage across the conductor 1 and the detection structure 2 can be expressed as uo = (Ra + R)*i + (La + L)*di / dt + Kv. Since the velocity equation 3, Kv = uo - (Ra + R)*i - (La + L)*di / dt, can be derived, it becomes possible to design a circuit that emulates equation 3 using the operational amplifier circuit 4 and realizes the Kv signal. According to Equation 3, the operational amplifier circuit 4 can receive the following three voltage signals: voltage uo, voltage Ra*i across Ra with gain (Ra+R) / Ra, and voltage La*di / dt across La with gain (La+L) / La. Circuit 4 generates an output Kv.

[0013] In Figure 1, it is assumed that the inductance L of the moving conductor 1 is constant. However, in reality, the inductance value of the moving conductor 1 is subject to frequency-dependent fluctuations. Therefore, in the following discussion, we will examine an improved approach to mitigate this problem.

[0014] Figure 2 is another circuit diagram of an embodiment of velocity detection, and includes a moving conductor in a magnetic field 1, a detection structure 2 connected to the moving conductor, a derived velocity equation 3, and a circuit with an operational amplifier 4. The voltage across the moving conductor 1 can be expressed as um = u1 + Kv, the voltage across the detection structure 2 can be expressed as u2, and the voltages across the conductor 1 and detection structure 2 can be expressed as u0 = u2 + u1 + Kv. If u2 = u1, then equation 3, Kv = 2um - uo, is obtained. Since equation 3 for calculating velocity has been obtained, it is necessary to generate a detection structure 2 that satisfies the condition u2 = u1, and it is also necessary to design an operational amplifier circuit 4 that emulates equation 3. A simple way to make the detection structure 2 is to use the exact same device as the moving conductor 1, but exclude the magnetic field or velocity. The operational amplifier circuit 4 has resistors R1 and R2, and capacitor C1 is used for circuit stabilization. To emulate equation 3 (Kv = 2um - uo), R1 = R2 should be set.

[0015] After acquiring a velocity signal from a moving conductor, this velocity signal can be used as a feedback mechanism to match the output of the moving conductor with the system's input signal. When the method shown in Figure 2 was applied to an experiment using a 6.5-inch dynamic speaker, it was confirmed that without velocity feedback, the output velocity deviated significantly from the input signal. On the other hand, integrating velocity feedback resulted in a significant change in the power amplifier output, thereby achieving accurate matching with the detected velocity signal.

[0016] Figure 3 shows the test results when a 100Hz half-sine wave is used as the system input signal. The photo on the left shows the test results without speed feedback, and the photo on the right shows the results with speed feedback. In both photos, the lower waveform shows the power amplifier output uo, and the upper waveform shows the speed.

[0017] Figure 4 shows the test results when a 100Hz ramp wave is used as the system input signal. The photo on the left shows the test results without speed feedback, and the photo on the right shows the results with speed feedback. In both photos, the lower waveform shows the power amplifier output uo, and the upper waveform shows the speed.

[0018] After obtaining an accurate velocity signal, the drive operation is significantly altered by a feedback mechanism, and the drive voltage is adjusted accordingly, allowing the speed of the moving conductor to precisely follow the input signal. With the development of a system that can intentionally distort the drive voltage, the previous efforts to produce hi-fi amplifiers with distortion reduced to several orders of magnitude seem to have become obsolete.

Claims

1. A method for detecting the velocity of a moving conductor in a magnetic field, The steps include electronically connecting a detection structure (2) to a moving conductor (1) in a magnetic field, The steps include: deriving a highly accurate mathematical formula (3) based on the characteristics of the moving conductor (1) and the detection structure (2), and calculating the velocity of the moving conductor (1); The process includes the step of designing a circuit equipped with an operational amplifier (4) that generates a velocity signal by emulating the derived equation (3), The detection structure (2) is a structure that enables the derivation of a high-precision mathematical formula (3) relating to speed, in a method.

2. A device for detecting the velocity of a moving conductor in a magnetic field, A moving conductor (1) in a magnetic field, A detection structure (2) electronically connected to the aforementioned moving conductor (1), A high-precision mathematical formula (3) derived to calculate the velocity of the moving conductor (1), The circuit includes an operational amplifier (4) capable of generating a speed signal by emulating the derived equation (3). The detection structure (2) is a device that enables the derivation of a high-precision mathematical formula (3) relating to speed.

3. The detection structure (2) has a physical structure similar to the moving conductor (1) in the magnetic field, but the magnetic field or motion is excluded from the detection structure (2). The method according to claim 1.

4. The detection structure (2) has a physical structure similar to the moving conductor (1) in the magnetic field, but the magnetic field or motion is excluded from the detection structure (2). The apparatus according to claim 2.

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