Temperature compensation method for electronic musical instrument and position detection circuit
Patent Information
- Application Number
- JP2023108252
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2023-06-30
- Publication Date
- 2025-01-17
Smart Images
Figure 2025007084000001_ABST
Abstract
Description
[Technical field]
[0001] The present invention relates to an electronic musical instrument and a temperature compensation method for a position detection circuit. [Background technology]
[0002] Patent Document 1 describes a position detection circuit for an electronic musical instrument keyboard device, which detects the position of an operator by using a magnetic sensor that displaces a magnet 8 (detection target) fixed to a key 2 (operator) relative to a coil. This position detection circuit generates a DC voltage in the coil according to the distance of the detection target from the coil, and the position of the operator can be detected by a detection unit such as a CPU according to the DC voltage.
[0003] Some magnetic sensors output an AC voltage from a coil according to the position of the operator (detected part). In this case, the position detection circuit converts the AC voltage from the magnetic sensor to a DC voltage using a rectifier diode or the like to make the output from the magnetic sensor a signal suitable for input to the detection part, and then further converts the DC voltage before outputting it to the detection part. A voltage drop occurs on the output (cathode) side of this rectifier diode compared to the input (anode) side by the forward voltage of the rectifier diode. [Prior art documents] [Patent documents]
[0004] [Patent Document 1] Japanese Utility Model Application Publication No. 02-111199 Summary of the Invention [Problem to be solved by the invention]
[0005] However, in the above technology, the forward voltage of the rectifier diode varies with the temperature of the rectifier diode, and the signal input to the detection unit also varies with the temperature, making it difficult to detect the exact position of the control from the signal.
[0006] SUMMARY OF THE PRESENT DISCLOSURE The present invention has been made in order to solve the above-mentioned problems, and has as its object to provide an electronic musical instrument and a method for compensating for temperature in a position detection circuit, which are capable of improving the detection accuracy of the position of an operator. [Means for solving the problem]
[0007] To achieve this object, the electronic musical instrument of the present invention comprises a controller whose position changes when operated by a player, a magnetic sensor that outputs an AC voltage in response to the change in position of the controller, a rectifier diode whose anode receives the AC voltage from the magnetic sensor and whose cathode outputs a rectified voltage, calculation means for calculating a compensation voltage from a forward voltage generated in the diode when a predetermined voltage is applied in the forward direction, and compensation means for applying the compensation voltage calculated by the calculation means to the anode or cathode side of the rectifier diode when the AC voltage from the magnetic sensor is being input, and the position of the controller is detected in response to the voltage from the rectifier diode to which the compensation voltage has been applied by the compensation means.
[0008] The temperature compensation method for a position detection circuit of the present invention is a method for an electronic musical instrument that includes a controller whose position changes when operated by a player, a magnetic sensor that outputs an AC voltage in response to the change in position of the controller, and a rectifier diode to which the AC voltage from the magnetic sensor is input to the anode and which outputs a rectified voltage from the cathode, and includes a calculation step of calculating a compensation voltage from a forward voltage generated in a diode to which a predetermined voltage is applied in the forward direction, and a compensation step of applying the compensation voltage calculated in the calculation step to the anode or cathode side of the rectifier diode in a state in which the AC voltage from the magnetic sensor is input, and the position of the controller is detected in response to the voltage from the rectifier diode to which the compensation voltage has been applied in the compensation step. [Brief description of the drawings]
[0009] [Figure 1] 1 is a cross-sectional view of an electronic musical instrument according to a first embodiment. [Diagram 2]2 is a block diagram showing the electrical configuration of the electronic musical instrument; [Diagram 3] FIG. 2 is a diagram illustrating a schematic diagram of a position detection circuit. [Figure 4] FIG. 11 is a diagram showing the voltage state of each part when temperature compensation is not performed. [Diagram 5] FIG. 4 is a diagram showing the voltage state of each part when temperature compensation is performed. [Figure 6] FIG. 11 is a diagram showing a schematic diagram of a position detection circuit of an electronic musical instrument according to a second embodiment. [Figure 7] 13 is a diagram showing voltage states of various parts of the second embodiment when temperature compensation is performed. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0010] Preferred embodiments will now be described with reference to the accompanying drawings. First, an electronic musical instrument 10 according to a first embodiment will be described with reference to Fig. 1. Fig. 1 is a cross-sectional view of the electronic musical instrument 10. In the following description, the side closest to the player (the left side in Fig. 1) will be referred to as the front side of the electronic musical instrument 10, and the opposite side (the right side in Fig. 1) will be referred to as the rear side.
[0011] The electronic musical instrument 10 is a keyboard instrument (synthesizer) equipped with a plurality of keys 11 (operators) extending in the front-rear direction. The plurality of keys 11 are composed of a plurality of (52 in this embodiment) white keys 11a for playing fundamental tones and a plurality of (36 in this embodiment) black keys 11b for playing derived tones. These plurality of white keys 11a and black keys 11b are arranged in the scale direction (the direction perpendicular to the paper surface of FIG. 1). Note that FIG. 1 shows a cross section of the electronic musical instrument 10 cut on a plane perpendicular to the scale direction. In this embodiment, a total of 88 keys 11 are provided, but a configuration in which, for example, 76 or 61 keys 11 are provided may also be used.
[0012] The electronic musical instrument 10 has a chassis 13 fixed to the upper surface of a flat bottom plate 12, and a number of keys 11 attached to the chassis 13 via support members 14. The bottom plate 12 and the chassis 13 are each formed to extend in the scale direction using synthetic resin, wood, steel plate, etc. The chassis 13 is formed in a box shape with an open bottom, and the bottom surface is closed by the bottom plate 12.
[0013] The support member 14 is for rotatably supporting the key 11, and is fixed to the rear end side of the upper surface of the chassis 13. The support structure of the white key 11a by the support member 14 and the method of detecting the position of the white key 11a are described below, but these structures and methods are substantially the same for the black key 11b.
[0014] The support member 14 rotatably supports the white key 11a by inserting a rotation shaft 15 along the scale direction into a through hole 11c provided at the rear end of the white key 11a. In front of the rotation shaft 15, a coil spring 16 is sandwiched vertically between the white key 11a and the support member 14.
[0015] When the player presses the white key 11a, the coil spring 16 is elastically deformed. When the white key 11a is released from this state, the elastic recovery force of the coil spring 16 returns the white key 11a to its initial position. When the white key 11a is pressed and released (operated), the displacement member 17 is linked to the rotation of the white key 11a around the rotation shaft 15, and the displacement of the displacement member 17 is detected by the magnetic sensor 31 of the position detection circuit 30. The position detection circuit 30 is mainly formed on a flat board 18 placed on the top surface of the bottom plate 12, and will be described in detail later.
[0016] The displacement member 17 is supported by a holder 19 in a space surrounded by the bottom plate 12 and the chassis 13. The holder 19 stands up from a substrate 18, and has a shaft portion 19a provided at its upper end. The shaft portion 19a extending along the scale direction is inserted into an insertion hole 17a provided on the upper side of the displacement member 17, whereby the displacement member 17 is rotatably supported by the holder 19.
[0017] A protrusion 11d protrudes downward from the underside of the white key 11a, and a pin 11e protrudes from the lower end of the protrusion 11d in the scale direction. This pin 11e fits slidably into a groove 17b provided in the displacement member 17. As a result, when the white key 11a is pressed, the displacement member 17 rotates forward around the shaft 19a. On the other hand, when the white key 11a is released, the displacement member 17 rotates backward around the shaft 19a.
[0018] The magnetic sensor 31 includes a detected portion 32 provided under the displacement member 17, and a coil 33 provided on the upper surface of the substrate 18. When the displacement member 17 rotates in response to the operation of the white key 11a, the detected portion 32 is displaced relative to the coil 33.
[0019] More specifically, as the white key 11a is pressed downward, the amount of penetration of the detectable part 32 into the area facing the coil 33 (hereinafter referred to as the "detection area") increases. The amount of penetration of the detectable part 32 refers to the area where the detectable part 32 and the coil 33 face each other in the thickness direction of the board 18. The amount of penetration of the detectable part 32 is minimum when the white key 11a is in the initial position where it is not pressed, and is maximum when the white key 11a is pressed all the way down.
[0020] The detected part 32 is a conductor formed using a conductive material (such as copper). Therefore, when an AC voltage is applied to the coil 33 to generate a magnetic field, if the penetration amount of the detected part 32 into the detection area increases, the inductance of the coil 33 decreases. On the other hand, if the penetration amount decreases, the inductance of the coil 33 increases. The increase or decrease in inductance causes the peak value of the AC voltage output from the coil 33 to vary.
[0021] That is, the peak value of the AC voltage output from the coil 33 of the magnetic sensor 31 varies depending on the position of the white key 11a. Therefore, the electronic musical instrument 10 can detect the position of the white key 11a by appropriately acquiring the variation in the peak value of this AC voltage using the position detection circuit 30. By accurately detecting the position of this white key 11a, the electronic musical instrument 10 can determine the position of the piano action jack, define the aftertouch area, and so on.
[0022] Next, the electrical circuitry of the electronic musical instrument 10, including the position detection circuit 30, will be described with reference to Fig. 2. Fig. 2 is a block diagram showing the electrical configuration of the electronic musical instrument 10 and devices connected to the electronic musical instrument 10.
[0023] The electronic musical instrument 10 includes a CPU 21 (Central Processing Unit), a ROM 22 (Read Only Memory), a RAM 23 (Random Access Memory), an operation panel 24, an ADC 25 (Analog-Digital Converter), and a MIDI interface (I / F) 26. These components 21 to 26 are electrically connected to each other.
[0024] The ROM 22 is a memory for storing the control program executed by the CPU 21. The RAM 23 is a memory for rewritably storing various work data, flags, etc. when the control program is executed by the CPU 21. The operation panel 24 is provided with a plurality of operators for tuning the performance information generated by the electronic musical instrument 10.
[0025] One position detection circuit 30 and one ADC 25 are provided for each of the eight keys 11. The position detection circuit 30 acquires the output from a magnetic sensor 31 provided for each key 11 in a time-division manner and outputs it to the ADC 25. The ADC 25 is a converter that samples the analog voltage signal output from the position detection circuit 30 at predetermined intervals and converts it into a digital signal readable by the CPU 21. The ADC 25 may be built into the CPU 21.
[0026] The MIDI interface 26 is an interface that outputs performance information conforming to the MIDI standard in response to the operation of the multiple keys 11 (detection results of the position detection circuit 30). A sound source 27 connected to this MIDI interface 26 outputs musical tone signals in response to the input performance information. The output musical tone signals are amplified by an amplifier 28 and output by a speaker 29. Note that the sound source 27 to the speaker 29 may not necessarily be provided externally to the electronic musical instrument 10, but may be built into the electronic musical instrument 10.
[0027] Next, a detailed configuration of the position detection circuit 30 will be described with reference to Figs. 3 to 5. Fig. 3 is a diagram showing a schematic diagram of the position detection circuit 30. Fig. 4 is a diagram showing the voltage state of each part of the position detection circuit 30 when temperature compensation is not performed. Fig. 5 is a diagram showing the voltage state of each part of the position detection circuit 30 when temperature compensation is performed. Note that the vertical axis of Figs. 4 and 5 represents voltage, and the horizontal axis of Figs. 4 and 5 represents time. Also, graphs A to F in Figs. 4 and 5 are graphs of voltage at positions A to F shown in Fig. 3.
[0028] 3, the position detection circuit 30 is a circuit that converts the AC voltage output from the coil 33 of the magnetic sensor 31 into a voltage suitable for input to the ADC 25. This suitable voltage is a DC voltage that corresponds to the peak value of the AC voltage from the coil 33. This is because the voltage at the time of sampling by the ADC 25 corresponds to that peak value, and the CPU 21 detects the position of the key 11 based on the digital signal of that peak value.
[0029] The position detection circuit 30 mainly includes a magnetic sensor 31, an AC coupling 35, a rectifier diode 36, a smoothing circuit 37, an LPF (low pass filter) 38, and a temperature compensation circuit 40. First, with reference to Figures 3 and 4, a case where the temperature compensation circuit 40 (a circuit connected from below to position B in Figure 3) is not present and no temperature compensation is performed will be described.
[0030] The magnetic sensor 31 includes an amplifier 34 for amplifying and outputting the AC voltage output from the coil 33. The coil 33 and the amplifier 34 are connected to the same ground (reference potential 0V). The amplifier 34 is not limited to being built into the magnetic sensor 31, and may be provided outside the magnetic sensor 31.
[0031] The output side of the magnetic sensor 31 (amplifier 34) is connected to the rectifier diode 36 via the capacitor C1 of the AC coupling 35. Although not shown, a switch is provided between the eight magnetic sensors 31 and the capacitor C1 to select one of the outputs of the eight magnetic sensors 31 and input it to the capacitor C1. If the amplifier 34 is provided outside the magnetic sensor 31, the switch can be provided between the eight coils 33 and the amplifier 34. In this case, the number of amplifiers 34 can be reduced relative to the number of keys 11, and the position detection circuit 30 can be made smaller and less expensive.
[0032] The capacitor C1 passes the AC current from the magnetic sensor 31 as is. Therefore, the voltage at a position A between the magnetic sensor 31 and the capacitor C1 and the voltage at a position B between the capacitor C1 and the rectifier diode 36 become the same.
[0033] The rectifier diode 36 is a pn junction type semiconductor that allows current to flow easily in the forward direction from the anode to the cathode, but does not allow current to flow in the reverse direction. In the following description, the forward voltage is defined as positive (+) and the reverse voltage is defined as negative (-).
[0034] The anode of the rectifier diode 36 is connected to the output side of the magnetic sensor 31 via the capacitor C1. As a result, the rectifier diode 36 half-wave rectifies the AC voltage input to the anode from the magnetic sensor 31, converts it into a pulsating voltage, and outputs the voltage from the cathode.
[0035] The smoothing circuit 37 is a circuit that smoothes the pulsating voltage output from the cathode of the rectifier diode 36, and is connected between the cathode and the LPF 38. The smoothing circuit 37 includes a capacitor C2 and a resistor R1. The capacitor C2 and the resistor R1 are provided in parallel between the ground and each of the branches of the electric wire connecting the rectifier diode 36 and the LPF 38. The smoothing circuit 37 charges the capacitor C2 up to the peak of the input pulsating current, and when the peak is exceeded, the capacitor C2 gradually discharges to the resistor R1, so that a smoothed pulsating current can be output.
[0036] A known envelope detection circuit is formed by the rectifier diode 36 and the smoothing circuit 37. As shown in Fig. 4, the voltage at point C output from the envelope detection circuit (smoothing circuit 37) becomes an envelope near the positive peak of the voltage at point B. The peak value of this envelope is slightly lower than the peak of the voltage at point B.
[0037] This is because a forward voltage drop occurs due to the rectifier diode 36. This forward voltage is the voltage that occurs across the rectifier diode 36 when a forward current flows through the rectifier diode 36. If the potential difference between the anode and cathode of the rectifier diode 36 is equal to or less than the forward voltage, no current flows through the rectifier diode 36. On the other hand, if it is greater than the forward voltage, a voltage drop of the forward voltage occurs on the cathode side relative to the anode side.
[0038] Furthermore, the higher the temperature of the rectifier diode 36, the smaller the forward voltage of the rectifier diode 36 and the larger the voltage at position C. Thus, in Fig. 4, the voltage at position C when the temperature is about 25°C is shown by a dashed line, and temperatures higher than the dashed line are shown by a one-dot chain line, and temperatures lower than the dashed line are shown by a two-dot chain line. This relationship is the same for the voltage at position D in Fig. 4 and the voltages at positions B, F, and G in Figs. 5 and 7.
[0039] LPF 38 passes frequencies below a cutoff frequency of the voltage input from smoothing circuit 37, while blocking (reducing) frequencies equal to or higher than the cutoff frequency, and outputs the result to ADC 25. This cutoff frequency is set to a value lower than the frequency of coil 33 so that the frequency component of the voltage output from coil 33 is blocked.
[0040] As a result, the voltage at position D output from LPF 38 becomes a DC voltage based on the peak value of the voltage at position C. More specifically, the voltage at position D is a value obtained by amplifying the peak value voltage at position C by a predetermined amplification factor. Note that the amplification factor by LPF 38 may be changed as appropriate, or may be 1.
[0041] The DC voltage at position D is sampled by the ADC 25, and based on the sampling result (value of the DC voltage), the CPU 21 detects the position of the key 11. However, if temperature compensation is not performed, the DC voltage at position D varies depending on the temperature of the rectifier diode 36, and the detection result of the position of the key 11 by the CPU 21 varies depending on the temperature.
[0042] The temperature compensation circuit 40 is a circuit for compensating for this temperature variation. Hereinafter, the temperature compensation circuit 40 (when performing temperature compensation) will be described with reference to Figures 3 and 5. The temperature compensation circuit 40 includes a reference voltage circuit 41, a temperature compensation diode 42, a resistor R2, and a subtraction circuit 43.
[0043] The reference voltage circuit 41 is a circuit that continues to output a constant DC voltage Vref with respect to a reference potential, regardless of the power supply voltage, temperature, etc. In this embodiment, the DC voltage Vref is the voltage at position E, and is set to be equal to the peak value of the positive voltage at position A when the key 11 is in the initial position. The reference voltage circuit 41 outputs the DC voltage Vref based on a command from the CPU 21.
[0044] The temperature compensation diode 42 is provided separately from the rectifier diode 36, and is configured to have the same characteristics as the rectifier diode 36. The anode of the temperature compensation diode 42 is connected to the output side of the reference voltage circuit 41, and the cathode of the temperature compensation diode 42 is connected to a resistor R2. The resistor R2 is provided to adjust the value of the current flowing through the temperature compensation diode 42.
[0045] Like the rectifier diode 36, the temperature compensating diode 42 also generates a forward voltage that varies depending on the temperature of the temperature compensating diode 42. Therefore, the voltage at position F on the output side of the resistor R2 drops from the voltage at position E by the forward voltage of the temperature compensating diode 42 and the voltage applied to the resistor R2. Note that the voltage of the resistor R2 is sufficiently small compared to the forward voltage of the temperature compensating diode 42, so it can be ignored. In other words, the difference obtained by subtracting the voltage at position F from the voltage at position E is the forward voltage of the temperature compensating diode 42.
[0046] The subtraction circuit 43 (calculation means) is a circuit for calculating the forward voltage of this temperature compensation diode 42. The subtraction circuit 43 includes an operational amplifier 44 and resistors R3 to R6. The inverting input terminal (-) of the operational amplifier 44 is connected to the output side (position F) of the resistor R2 via the resistor R3. A branch from between the inverting input terminal of the operational amplifier 44 and the resistor R3 is connected to the output terminal of the operational amplifier 44 (the right end of the operational amplifier 44 in FIG. 3) via the resistor R4.
[0047] A branch from between the reference voltage circuit 41 and the temperature compensation diode 42 (position E) is connected via a resistor R5 to the non-inverting input terminal (+) of the operational amplifier 44. A branch from between the resistor R5 and the non-inverting input terminal of the operational amplifier 44 is connected to ground via a resistor R6.
[0048] Since the resistance values of the resistors R3 to R6 are substantially the same, the subtraction circuit 43 outputs from the output terminal the forward voltage of the temperature compensation diode 42 (the voltage at position G) obtained by subtracting the voltage at position F from the voltage at position E (calculation step). This forward voltage is a compensation voltage for temperature compensating the rectifier diode 36.
[0049] An output terminal of the subtraction circuit 43 is connected between the capacitor C1 and the anode of the rectifier diode 36 (position B) via a joining wire 45. A resistor R7 is provided in the middle of this joining wire 45, between positions G and B. The resistor R7 and the capacitor C1 form an AC coupling 35 (high-pass filter).
[0050] The capacitance of capacitor C1 and the resistance of resistor R7 are set so that AC coupling 35 (compensation means) passes the AC voltage from magnetic sensor 31 while blocking the DC compensation voltage from subtraction circuit 43. As a result, the voltage at position B becomes the AC voltage from magnetic sensor 31 (voltage at position A) plus the compensation voltage (voltage at position G) (compensation step). In other words, the voltage at position B is the voltage at position A with the center of amplitude shifted to the positive side by the compensation voltage.
[0051] The hotter the temperature compensation diode 42 is, the smaller the compensation voltage at position G becomes, and similarly the voltage shift at position B becomes smaller. When the voltage at position B drops due to the forward voltage of the rectifier diode 36, the hotter the rectifier diode 36 is, the smaller the voltage drop becomes.
[0052] That is, the forward voltage of the rectifier diode 36, which is subtracted (voltage drop) from the AC voltage from the magnetic sensor 31, and the compensation voltage of the temperature compensation diode 42, which is added to the AC voltage from the magnetic sensor 31, fluctuate in the same manner according to temperature. As a result, the temperature dependency of the voltage drop by the rectifier diode 36 can be cancelled out by the temperature dependency of the compensation voltage added to the anode side of the rectifier diode 36.
[0053] As a result, when temperature compensation is performed, the voltages at positions C and D are less susceptible to fluctuations due to the temperature of the rectifier diode 36. This reduces the temperature dependency of the detection results of the position detection circuit 30 that are input to the CPU 21 via the ADC 25. Therefore, the electronic musical instrument 10 can improve the accuracy of detecting the position of the key 11 based on the detection results.
[0054] The compensation voltage for canceling the temperature dependency of the rectifier diode 36 is not calculated by the CPU 21 or the like, but as described above, is calculated by hardware called the temperature compensation circuit 40. This reduces the load on the CPU 21 for calculating the compensation voltage.
[0055] Furthermore, if the compensation voltage is DC, the temperature compensation circuit 40 can be connected to the anode of the rectifier diode 36 by AC coupling 35. Since the CPU 21 is not involved in the input of the compensation voltage to the anode of the rectifier diode 36, the load on the CPU 21 can be reduced.
[0056] Furthermore, as a circuit for adding a compensation voltage to the AC voltage from the magnetic sensor 31, for example, an adder circuit including an operational amplifier may be used in place of the AC coupling 35. However, using the AC coupling 35 can simplify the circuit configuration, and can reduce the cost and size of the position detection circuit 30.
[0057] Each of the multiple position detection circuits 30 is provided with a rectifier diode 36 and a temperature compensation diode 42 in a one-to-one relationship. This allows the rectifier diode 36 and the temperature compensation diode 42 for compensating for the voltage drop caused by the rectifier diode 36 to be located close to each other, making it easier to bring the temperatures of the diodes 36, 42 close to each other. As a result, the temperature dependency of the detection result of the position detection circuit 30 can be reduced, and the detection accuracy of the position of the key 11 can be improved.
[0058] Furthermore, the rectifier diode 36 and the temperature compensation diode 42, which are provided in a one-to-one relationship, are sealed in the same sealing material 46 and assembled into one chip. The diodes 36, 42 in the one chip are thermally coupled to each other and have substantially the same temperature, and can be said to be composed of diodes with substantially the same temperature dependence of their forward voltages. As a result, the forward voltages of the diodes 36, 42 can be made substantially the same regardless of temperature, and the temperature dependence of the detection results of the position detection circuit 30 can be further reduced. As a result, the accuracy of detecting the position of the key 11 can be further improved.
[0059] The forward voltage of each of the diodes 36, 42 also depends on the value of the forward current (hereinafter referred to as the “current value”) flowing through each of the diodes 36, 42. The current value varies according to the voltage input to each of the diodes 36, 42.
[0060] When the key 11 is in its initial position, the peak value of the AC voltage at position B input to the rectifier diode 36 and the DC voltage Vref input to the temperature compensation diode 42 are substantially the same, and the difference between them is small. This makes it possible to make the forward voltages of the diodes 36, 42 substantially the same near the peak values, making it easier to cancel out the voltage drop of the forward voltage of the rectifier diode 36 by the forward voltage (compensation voltage) of the temperature compensation diode 42. Therefore, when the key 11 is in its initial position, it is easier for the CPU 21 to detect (calculate) the position of the key 11 from the detection result of the position detection circuit 30.
[0061] When the key 11 is operated from the initial position, the peak value of the AC voltage at position B fluctuates with respect to the constant DC voltage Vref, resulting in a slight difference in the forward voltage of each of the diodes 36, 42 compared to when the key 11 is in the initial position. Although this difference also has temperature dependency, the difference itself is small and therefore has little effect on the detection accuracy of the position of the key 11. On the other hand, inputting a constant DC voltage Vref makes it easier to control the position detection circuit 30 and reduces costs compared to when the DC voltage Vref is varied in response to the operation of the key 11.
[0062] Even if the diodes 36, 42 are thermally coupled, it is preferable to make the amounts of heat generated by the diodes 36, 42 approximately the same to reduce the temperature difference between the diodes 36, 42. The amount of heat generated (temperature) mainly depends on the current value of each of the diodes 36, 42.
[0063] The current value of the temperature compensation diode 42 is determined mainly by the magnitude of the DC voltage Vref input to the temperature compensation diode 42 and the resistance values of the resistors R2 to R6. It is preferable to adjust the resistance values of the resistors R2 to R6 so that this current value is the same as the current value of the rectifier diode 36 to which the peak value of the AC voltage at position B when the key 11 is in the initial position is input. This makes it possible to bring the heat values (temperatures) of the diodes 36, 42 closer together, further improving the accuracy of detecting the position of the key 11.
[0064] In this embodiment, the resistor R2, which is one of the resistors for adjusting the current value (heat generation amount) of the temperature compensation diode 42, is provided outside the subtraction circuit 43. This makes it easier to adjust (change) the resistance value of the resistor R2, and therefore easier to adjust the current value of the temperature compensation diode 42.
[0065] Next, a second embodiment will be described with reference to Fig. 6 and Fig. 7. The same parts as those in the first embodiment are given the same reference numerals and their description will be omitted. Fig. 6 is a diagram showing a schematic diagram of a position detection circuit 50 of an electronic musical instrument in the second embodiment. Fig. 7 is a diagram showing the voltage state of each part of the position detection circuit 50 when temperature compensation is performed.
[0066] The electronic musical instrument of the second embodiment has the same configuration as the electronic musical instrument of the first embodiment, except for a temperature compensation circuit 51 in a position detection circuit 50. The temperature compensation circuit 51 is different from the temperature compensation circuit 40 of the first embodiment in that a branch wire 52 and an offset power supply 54 are provided instead of the reference voltage circuit 41.
[0067] The branch electric wire 52 is an electric wire branched off from between the magnetic sensor 31 and the capacitor C1 (position A), and is connected to the anode of the temperature compensation diode 42. As a result, the voltage at position A is input to the temperature compensation diode 42. Therefore, the compensation voltage at position G is basically determined by the subtraction circuit 43 to be the forward voltage of the temperature compensation diode 42 when the voltage at position A is input.
[0068] The offset power supply 54 is a DC power supply provided to approximate the compensation voltage to DC. The offset power supply 54 is provided between the magnetic sensor 31 and the ground of the magnetic sensor 31. The offset power supply 54 adds a DC offset voltage to the AC voltage output from the magnetic sensor 31.
[0069] Since the offset voltage is a direct current, it is removed when it passes through the capacitor C1 of the AC coupling 35. As a result, the voltage at position B becomes the AC voltage output from the magnetic sensor 31 plus the compensation voltage, and the offset voltage is removed. This makes it possible to prevent the offset voltage from significantly affecting the detection result of the position detection circuit 50.
[0070] The offset voltage is a positive voltage that makes the entire voltage at position A equal to or greater than the forward voltage of temperature compensation diode 42. For example, if the minimum value of the voltage at position A is approximately -1.5 V and the forward voltage of temperature compensation diode 42 at 25°C is approximately 0.3 V, the offset voltage is set to 2.2 V taking into account fluctuations and errors in the forward voltage.
[0071] Here, if no offset voltage is added to the AC voltage from the magnetic sensor 31, the compensation voltage, which is the difference between the voltage at position A and the voltage at position F, is approximately constant mainly when the voltage at position A is positive, and fluctuates significantly to the negative side mainly when the voltage at position A is negative. That is, the compensation voltage becomes a pulsating current with a sufficiently large amplitude compared to the AC voltage from the magnetic sensor 31, and deviates significantly from the forward voltage of the temperature compensation diode 42. With such a compensation voltage, there is a risk that the rectifier diode 36 cannot be appropriately temperature compensated.
[0072] In contrast, when an offset voltage is added to the AC voltage from the magnetic sensor 31, it is possible to prevent a part of the voltage at position A from being rectified by the temperature compensation diode 42. As a result, the entire voltage at position F fluctuates along with the voltage at position A, and the compensation voltage at position G is approximated to DC and indicates the forward voltage of the temperature compensation diode 42.
[0073] This compensation voltage fluctuates slightly according to fluctuations in the voltage at position A (AC voltage from the magnetic sensor 31) input to the temperature compensation diode 42. However, the amplitude of the compensation voltage is sufficiently small (1 / 20 or more and 1 / 10 or less) compared to the amplitude of the AC voltage from the magnetic sensor 31, so the compensation voltage can be considered as DC. This allows the compensation voltage to be added to the AC voltage from the magnetic sensor 31 by the AC coupling 35.
[0074] As described above, according to the position detection circuit 50 of the second embodiment, by providing the branch electric wire 52 and the offset power supply 54, it is possible to apply a voltage to the temperature compensation diode 42 without going through the CPU 21, unlike the first embodiment. In other words, the temperature compensation of the position detection circuit 50 can be performed only by hardware, and the load on the CPU 21 can be further reduced.
[0075] In the first embodiment, when the key 11 is operated from the initial position, the peak value of the voltage at position B input to the rectifier diode 36 fluctuates with respect to the constant DC voltage Vref input to the temperature compensation diode 42, resulting in a difference in the forward voltages of the diodes 36, 42.
[0076] In contrast, in the second embodiment, the peak value of the voltage at position A input to the temperature compensation diode 42 also varies in response to the operation of the key 11, just like the voltage at position B. This makes it difficult for a difference to occur in the forward voltages of the diodes 36, 42, even when the key 11 is operated from the initial position. This reduces the temperature dependency of the detection result of the position detection circuit 50, which is based on the temperature dependency of that difference, thereby improving the detection accuracy of the position of the key 11.
[0077] The above has been explained based on the above embodiment, however, the present invention is in no way limited to the above embodiment, and it can be easily inferred that various improvements and modifications are possible within the scope that does not deviate from the spirit of the present invention.
[0078] In the above embodiment, the AC voltage output from the magnetic sensor 31 varies in response to the displacement of the displacement member 17 interlocked with the key 11, but the present invention is not limited to this. For example, the displacement member 17 may be omitted, and the positions of the detection target 32 and the coil 33 may be appropriately changed so that the AC voltage output from the magnetic sensor 31 varies in response to the displacement of other displacement members such as the hammer (which is interlocked with the key 11 and provides a feeling when the key is pressed) and the key 11. Furthermore, the magnetic sensor 31 is not limited to the one described in the above embodiment, so long as it can output an AC voltage corresponding to the position of the operator. The magnetic sensor 31 may be configured to increase or decrease the output value by changing the distance between the detection target and the detection unit, instead of the configuration in which the output value increases or decreases as the amount of penetration of the detection target 32 into the detection area increases or decreases. Furthermore, an optical sensor, a capacitance sensor, or the like may be used instead of the magnetic sensor 31, as long as it is a sensor that can output an AC voltage corresponding to the position of the operator.
[0079] In the above embodiment, the electronic musical instrument 10 is a synthesizer, and the position (operation amount) of the key 11 is detected by the magnetic sensor 31 and the position detection circuits 30, 50. However, this is not necessarily limited to the above. For example, the magnetic sensor 31 and the position detection circuits 30, 50 may be provided in other keyboard electronic musical instruments. Also, the magnetic sensor 31 and the position detection circuits 30, 50 may be used to detect the positions of operators, foot keys, pedals, etc., provided on the operation panel 24, in addition to the keys 11.
[0080] In electronic musical instruments other than keyboard instruments, such as percussion instruments, wind instruments, and string instruments, the position of the operator may be detected by the magnetic sensor 31 and the position detection circuits 30, 50. Also, in various devices other than electronic musical instruments, the position of the operator may be detected by the magnetic sensor 31 and the position detection circuits 30, 50.
[0081] In the above embodiment, a case has been described in which one position detection circuit 30 and one ADC 25 are provided for every eight keys 11, but this is not necessarily limited to the above. One position detection circuit 30 may be provided for every one to seven or nine or more keys 11. Also, one ADC 25 may be provided for every two or more position detection circuits 30. In this case, the ADC 25 may obtain the output from the position detection circuit 30 in a time-division manner.
[0082] The fewer the position detection circuits 30 and ADCs 25, the lower the cost and the smaller the electronic musical instrument 10. On the other hand, the more the position detection circuits 30 and ADCs 25, the fewer the number of time divisions, improving the responsiveness of position detection for each key 11. To achieve both, it is preferable to provide one position detection circuit 30 and one ADC 25 for every 4 to 12 keys 11.
[0083] In the above embodiment, the rectifier diode 36 and the temperature compensation diode 42 (temperature compensation circuit 40, 51) are provided in a one-to-one relationship, but this is not necessarily limited to this. A configuration in which a plurality of rectifier diodes 36 and one temperature compensation diode 42 (temperature compensation circuit 40, 51) form one pair is also possible. In this case, it is preferable to limit the number of rectifier diodes 36 in one pair to, for example, eight or less, so that the temperatures of the diodes 36, 42 in one pair are close to each other. In comparison with the case in which the diodes 36, 42 are provided in a one-to-one relationship, providing the diodes 36, 42 in a multi-to-one relationship reduces the number of temperature compensation diodes 42 (temperature compensation circuits 40, 51), and the cost and size of the position detection circuits 30, 50 can be reduced.
[0084] In the above embodiment, the compensation voltage from the temperature compensation circuits 40, 51 is applied to the anode side of the rectifier diode 36. However, the compensation voltage may be applied to the cathode side of the rectifier diode 36. The cathode side refers to the area between the rectifier diode 36 and the smoothing circuit 37, between the smoothing circuit 37 and the LPF 38 (position C), and between the LPF 38 and the ADC 25 (position D).
[0085] The method of applying the compensation voltage is not limited to applying it to the anode side or the cathode side of the rectifier diode 36 by the AC coupling 35, and may be changed. For example, the compensation voltage may be applied to the anode side or the cathode side of the rectifier diode 36 by a known adder circuit using an operational amplifier.
[0086] Also, a configuration (compensation means, compensation step) may be used in which the compensation voltage calculated by the temperature compensation circuit 40, 51 is input to the CPU 21, and the compensation voltage is added to the anode side or cathode side of the rectifier diode 36 via the CPU 21. When the compensation voltage is added via the CPU 21, the compensation voltage can be corrected by the CPU 21 in accordance with the difference in temperature dependency of each of the diodes 36, 42, the difference in the current value of each of the diodes 36, 42, the operation amount of the operator, etc. Also, a configuration (compensation means, compensation step) may be used in which the CPU 21 adds the compensation voltage to the value acquired from the ADC 25. In this case, too, it can be said that the compensation voltage is added to the cathode side of the rectifier diode 36.
[0087] In the above first embodiment, the DC voltage Vref output from the reference voltage circuit 41 is set to the peak value of the positive voltage at position A when the key 11 is in the initial position, but this is not necessarily limited to this. For example, a fixed voltage unrelated to the peak value may be set as the DC voltage Vref. The fixed voltage may be equal to or greater than the forward voltage of the temperature compensation diode 42. The DC voltage Vref may also be varied according to the amount of operation of the operator detected by the CPU 21. In this case, as in the second embodiment, it is possible to make it difficult for a difference to occur in the forward voltages of the diodes 36, 42.
[0088] In the above embodiment, the rectifier diode 36 and the temperature compensation diode 42 are assembled into one chip, but this is not necessarily limited to this. For example, the rectifier diode 36 and the temperature compensation diode 42 for compensating for the voltage drop caused by the rectifier diode 36 may be encapsulated in separate sealing materials. The diodes 36 and 42 provided in a multi-to-one relationship may be assembled into one chip, or may be encapsulated in separate sealing materials.
[0089] When the diodes 36, 42 are encapsulated in separate encapsulants, it is preferable that the diodes 36, 42 are configured with diodes having the same electrical characteristics, particularly the same forward voltage, at a predetermined temperature (e.g., 25° C.). This makes it easier to cancel out the temperature dependence of the forward voltages of the diodes 36, 42 from each other.
[0090] It is more preferable that the diodes 36, 42 are configured from diodes having the same specifications and lot numbers. Note that a lot number is a management number given to a certain number of products when producing products with the same specifications. If the specifications and lot numbers are the same, it can be said that the temperature dependence of the diodes 36, 42 is approximately the same. As a result, it is possible to more easily cancel out the temperature dependence of the forward voltage of each of the diodes 36, 42 by each other.
[0091] Even if the diodes 36, 42 are not integrated into one chip, it is preferable to thermally couple the diodes 36, 42. Examples of this thermal coupling include arranging the diodes 36, 42 on the same substrate, arranging the diodes 36, 42 adjacent to each other (within 5 mm), or contacting the diodes 36, 42 with each other. This allows the diodes 36, 42 to be in thermal equilibrium and to have substantially the same temperature, making it easier to cancel out the temperature dependence of the forward voltages of the diodes 36, 42.
[0092] In the above embodiment, the forward voltage (compensation voltage) of the temperature compensation diode 42 is calculated by the subtraction circuit 43 using the operational amplifier 44, but the present invention is not limited to this. For example, the voltage on the anode side and the voltage on the cathode side of the temperature compensation diode 42 may be input to the CPU 21, and the CPU 21 may calculate the compensation voltage (calculation means, calculation step). Furthermore, the resistance values of the resistors R3 to R6 of the subtraction circuit 43 are not limited to being the same, and may be different. In this case, the forward voltage of the temperature compensation diode 42 is amplified and used as the compensation voltage, and the magnitude of the compensation voltage can be adjusted by the subtraction circuit 43.
[0093] In the above embodiment, the compensation voltage is calculated using the temperature compensation diode 36, but the present invention is not limited to this. For example, a modified example may be used in which the temperature compensation circuit 40 from the reference voltage circuit 41 to the position G in FIG. 3 is omitted, and an electric wire from the CPU 21 is connected to the position G.
[0094] In this modification, during a "magnetic sensor non-driving time" when the CPU 21 does not apply an AC voltage to the coil 33, the CPU 21 inputs a DC voltage Vref to the resistor R7 via the junction wire 45. At this time, since the magnetic sensor 31 does not output an AC voltage, the output value of the ADC 25 is a voltage (Vref-Vf) obtained by dropping the forward voltage Vf of the rectifier diode 36 from the DC voltage Vref when the amplification factor of the LPF 38 is 1. Therefore, the CPU 21 calculates the forward voltage Vf (compensation voltage) of the rectifier diode 36, which is the difference between the DC voltage Vref and the output value of the ADC 25 (calculation means, calculation step), and stores it in the CPU 21 for each position detection circuit 30 (rectifier diode 36) and each magnetic sensor 31. If the amplification factor of the LPF 38 is other than 1, the CPU 21 converts the output value of the ADC 25 to a value before amplification, and calculates the compensation voltage based on the converted value and the DC voltage Vref.
[0095] Next, during the “magnetic sensor drive time” when the CPU 21 applies an AC voltage to the coil 33, the CPU 21 applies the compensation voltage calculated as described above to the resistor R7 via the junction wire 45 (compensation means, compensation step) to compensate for the voltage drop equivalent to the forward voltage Vf of the rectifier diode 36.
[0096] In this manner, in this modified example, temperature compensation can be performed by determining the forward voltage Vf (compensation voltage) of the rectifier diode 36 itself in a time-division manner. That is, the accuracy of detecting the position of the key 11 based on the detection result of the position detection circuit 30 can be improved while eliminating the need for the temperature compensation circuit 40. However, when the temperature compensation circuit 40 is used, the load on the CPU 21 can be reduced. [Explanation of symbols]
[0097] 10. Electronic Instruments 11 Keys (operators) 30,50 Position detection circuit 31 Magnetic Sensor 35 AC coupling (compensation means) 36 Rectifier Diode 42 Temperature Compensation Diode 43 Subtraction circuit (calculation means) 44 Operational Amplifiers 46 Encapsulating materials 52 Branch Wire 54 Offset Power Supply
Claims
1. A control whose position is changed by being operated by a player; a magnetic sensor that outputs an AC voltage in response to a change in the position of the operator; a rectifier diode that receives an AC voltage from the magnetic sensor at its anode and outputs a rectified voltage from its cathode; a calculation means for calculating a compensation voltage from a forward voltage generated in a diode when a predetermined voltage is applied in the forward direction; and compensation means for applying the compensation voltage calculated by the calculation means to an anode or cathode of the rectifier diode in a state in which an AC voltage from the magnetic sensor is being input, and the position of the operator is detected in accordance with the voltage from the rectifier diode to which the compensation voltage has been applied by the compensation means.
2. 2. The electronic musical instrument according to claim 1, wherein the diode used in the calculation means is a temperature compensation diode provided separately from the rectifier diode.
3. 3. The electronic musical instrument according to claim 2, wherein said calculation means is a subtraction circuit using an operational amplifier, which receives as input the voltage on the anode side of said temperature compensation diode and the voltage on the cathode side of said temperature compensation diode, and outputs the difference between these voltages as said compensation voltage from an output terminal.
4. 4. The electronic musical instrument according to claim 3, wherein the compensation means is an AC coupling formed by a capacitor connecting between the magnetic sensor and the rectifier diode, and a resistor connecting a branch between the capacitor and the rectifier diode to the output terminal of the operational amplifier.
5. a branch wire that branches off from the magnetic sensor side of the capacitor and is connected to the anode of the temperature compensation diode so that the voltage of the magnetic sensor side of the capacitor becomes the predetermined voltage; 5. The electronic musical instrument according to claim 4, further comprising an offset power supply which adds a DC offset voltage to the AC voltage output from said magnetic sensor, thereby making the entire predetermined voltage equal to or greater than a forward voltage of said temperature compensation diode.
6. 3. The electronic musical instrument according to claim 2, wherein said rectifying diode and said temperature compensating diode are diodes having the same specifications and lot numbers.
7. 7. The electronic musical instrument according to claim 2, wherein the rectifier diode and the temperature compensation diode are thermally coupled.
8. 8. The electronic musical instrument according to claim 7, wherein said rectifier diode and said temperature compensation diode are sealed in the same sealing material.
9. 2. The electronic musical instrument according to claim 1, wherein the diode used in the calculation means is the rectifier diode in a state where no AC voltage is input from the magnetic sensor.
10. A temperature compensation method for a position detection circuit in an electronic musical instrument including a control whose position changes when operated by a player, a magnetic sensor that outputs an AC voltage in response to the change in position of the control, and a rectifier diode that receives the AC voltage from the magnetic sensor at its anode and outputs a rectified voltage from its cathode, comprising: a calculation step of calculating a compensation voltage from a forward voltage generated in a diode when a predetermined voltage is applied in the forward direction; a compensating step of applying the compensation voltage calculated in the calculating step to an anode side or a cathode side of the rectifier diode in a state in which an AC voltage from the magnetic sensor is being input, and a position of the operator is detected in accordance with a voltage from the rectifier diode to which the compensation voltage has been applied in the compensating step.