1. Field of the Invention
Embodiments of the present invention generally relate to key speed detection systems and methods, and, in specific embodiments, to key speed detection systems and methods for an electronic musical instrument that detects an operating speed of an operation, such as pressing, releasing, and the like, of a key.
2. Related Art
In typical key operation speed detection devices for an electronic musical instrument, the operating speed of the keys is detected by the measurement of the time difference in which two or more switches, which have been disposed corresponding to each key, open and close. In the key operation speed detection device for an electronic musical instrument shown in FIG. 19, when the performer presses the key 1901 down, the key 1901 moves rotationally about the axis of rotation 1902. Then, the jack 1903 presses the common contact 1904 of the key switch down. The common contact 1904 is in contact with the contact 1905 during the time that the key is not pressed and then is separated from the contact 1905 and meets the contact 1906 due to the pressing of the key. The operating speed of the key is detected by the time from when the common contact 1904 is separated from the contact 1905 until the common contact meets the contact 1906. This method is widely used because the structure is simple. However, the key switch produces chatter. In addition, due to the wear and deformation of the key switch after a long period of use, the operating speed cannot be measured accurately.
In addition, other methods detect key speed based on changes in the strength of light or magnetism corresponding to the operation of the key and measuring these changes by means of various kinds of sensors. Japanese Laid-Open Patent Application Publication (Kokai) Number H10-26983 discloses a device having a slit disposed that changes the amount of light transmitted between a light emitting element and a light receptor element continuously in conformance with the change in the operating position of the key. Then, the operating position of the key is detected based on the light that is sensed by the light receptor element. With this device, two light intensity thresholds are set that correspond to two operating positions of the key. In addition, the time when the light intensity that is sensed by the light receptor element passes through these thresholds is measured.
A method that detects the strength of light or a magnetic field can also be used. However, optical and magnetic sensors are expensive and it is not possible to employ them in mainstream products. In addition, with optical and magnetic sensors, there is variation in the sensitivity between individual sensors and changes in the sensitivity due to changes in temperature and the like. Accordingly, operating positions and operating speeds are derived that differ from what was intended by the designer. In other words, the accurate operating speeds are not always measured as intended.
In Japanese Examined Patent Application Publication (Kokoku) Number S39-29485, the capacitance of a capacitor is changed in conformance with the operation of the key. Then, a signal that has passed through the capacitor is reshaped via a rectifier circuit and a differentiation circuit and the key operation speed is derived. This device requires a rectifier circuit, a differentiation circuit, and the like leading to a complicated configuration.
In Japanese Laid-Open Patent Application Publication (Kokai) Number H7-84576, a capacitance sensor that has been held by a retractable wire is acted on by the key operation. Then, the oscillation frequency of an oscillator is changed by the change in the capacitance. In addition, the oscillation frequency is converted into a voltage and the depth of the key pressing is detected by the detection of the voltage. This device requires a variable oscillator, a frequency to voltage converter, and the like leading to a complicated configuration.
In Japanese Laid-Open Patent Application Publication (Kokai) Number H9-204846, a capacitive analog switch that has been furnished with a coil spring is acted on by the key operation. Then, a signal that has passed through the capacitive analog switch is A/D converted after being amplified by an amplifier. Then, in addition, the key operation speed is derived from the change in the level of the signal that has been A/D converted. This device requires an amplifier, an A/D converter, and the like leading to a complicated configuration.
For other methods used in vernier calipers, rotary encoders, and the like to measure minute positions or rotation angles, two or more alternating voltages the phases of which are mutually different are each respectively applied to a plurality of electric field generating electrodes (transmission electrodes). Then, the capacitance between the electric field generating electrodes (the transmission electrodes) and the electric field detecting electrodes (the reception electrodes) is changed in conformance with the position or the angle of the object. Then the position or the angle of the object is derived by the detection of the change in the phase of the alternating voltage that is induced in the electric field detecting electrodes (the reception electrodes). This method is referred to hereinafter as a “capacitance-phase conversion method” (e.g., Japanese Examined Patent Application Publication (Kokoku) Number H4-67883, Japanese Examined Patent Application Publication (Kokoku) Number S64-11883, and Japanese Examined Patent Application Publication (Kokoku) Number H4-67882). Incidentally, in the explanations hereinafter, the electrode that generates an electric field is referred to as a “transmission electrode” and the electrode that detects an electric field is referred to as a “reception electrode.”
For example, in Japanese Examined Patent Application Publication (Kokoku) Number H4-67883, shown in FIG. 20(a), the transmission electrode 2002, the transmission electrode 2003 and the reception electrode 2005 are deployed. The transmission electrode 2002 is arranged so that the width gradually increases with respect to the circumferential direction on the outer peripheral surface of the cylinder 2001, which is configured with a dielectric. The transmission electrode 2003 is arranged so that, conversely, the width gradually decreases. The reception electrode 2005 is arranged in a concave section that has been formed in the outer peripheral surface of the rotor 2004 that rotates on the inside of the cylinder 2001. The alternating voltage 2006 and the alternating voltage 2007, the phases of which are mutually different, are applied to the transmission electrode 2002 and the transmission electrode 2003. Accordingly, the voltage that has been induced in the reception electrode 2005 is retrieved to the outside by the retrieval line 2008. A voltage in conformance with the capacitance that is formed between the transmission electrode 2002 and the reception electrode 2005 and the capacitance that is formed between the transmission electrode 2003 and the reception electrode 2005 is induced in the reception electrode 2005. The equivalent circuit for the configuration of FIG. 20(a) is shown in FIG. 20(b).
The potentials of the alternating voltage 2006 and the alternating voltage 2007 are made e1 and e2, respectively. In addition, the capacitance that is formed between the transmission electrode 2002 and the reception electrode 2005 and the capacitance that is formed between the transmission electrode 2003 and the reception electrode 2005 are made c1 and c2, respectively. The voltage V that is induced and synthesized in the reception electrode 2005 in that case becomes:V=(e1*c1+e2*c2)/(c1+c2)  [Equation 1]
In those cases where the phase difference of the alternating voltage 2006 and the alternating voltage 2007 has been made π (180 degrees), the voltage of the signal that is induced in the reception electrode 2005 changes in conformance with the capacitance c1 and the capacitance c2. In addition, in those cases where the phase difference of the alternating voltage 2006 and the alternating voltage 2007 has been made π/2 (90 degrees), the phase of the signal that is induced in the reception electrode 2005 changes in conformance with the capacitance c1 and the capacitance c2. As such, it is possible to derive the angle of rotation of the rotor from the change in the voltage or the phase.
In addition, in Japanese Examined Patent Application Publication (Kokoku) Number S64-1188, as shown in FIG. 21, the alternating voltages 3004, 3005, and 3006, the three respective phases of which differ mutually by 2π/3 (120 degrees), are alternately applied to the rectangular transmission electrodes 3001, 3002, and 3003, which have been lined up at a uniform interval. Then, the phase of the voltage that has been induced and synthesized in the reception electrode 3007, which moves facing the transmission electrodes, is measured continuously and the measurement precision of the precision vernier caliper structure is increased.
In those cases where the voltage is detected using alternating voltages that have inverse phases, (i.e., a phase difference of it) the measurement precision of the voltage (such as the sensitivity of the amplifier that amplifies the induced voltage and the like) becomes problematic. In addition, in those cases where the voltage is measured digitally, the precision of the A/D converter also becomes problematic. Furthermore, this configuration is complicated due to the use of an A/D converter. In those cases where the phase is detected using alternating voltages having phase differences such as π/2 or 2π/3 (because no A/D conversion is required), the sensitivity of the amplifier and the like does not become a problem. Thus, one can carry out high precision measurements with a simple configuration.
For a capacitance-phase conversion method used in a vernier caliper or a rotary encoder, there is no more than one phase or angle of the object that is the target of the measurement. However, in the case of an electronic musical instrument, a large number of keys (e.g., 88 keys or the like) are furnished for which detection of the operating speed of the key for each of the keys is done independently. If the circuits that generate the alternating voltages and the circuits that detect the voltage or the phase are furnished for each of this large number of keys, the configuration would become complicated and the cost would become high.
In addition, in the equivalent circuit of FIG. 20(b) that has been used in order to explain the principles of the capacitance-phase conversion method, only the capacitances c1 and c2 have been shown between the electrodes. However, as is shown by the broken line in FIG. 20(b), a capacitance c3 of about 10 pF exists that is composed of the stray capacitance of the wiring from the reception electrode to the phase measuring circuit, the input capacitance of the phase measuring circuit, and the like. Because of this, the voltage that is input to the phase measuring circuit is divided by the interelectrode capacitances c1 and c2 and the capacitance c3. In order for the voltage that is input to the phase measuring circuit to be made a satisfactory level, it is necessary to make the interelectrode capacitance large. To obtain a large capacitance, the electrode area may be made large, the interelectrode gap made small, a space not disposed in the interelectrode gap, or a material having a high dielectric constant interposed. In the device of Japanese Examined Patent Application Publication (Kokoku) Number H4-67883, because the inner circumferential surface of the cylinder 2002 and the outer circumferential surface of the rotor 2004 are placed in contact while making a cylinder 2002 with a dielectric, it is possible to obtain a large interelectrode capacitance.
In the case of a vernier caliper, or a rotary encoder and the like, even taking a configuration in which a dielectric body is interposed between the electrodes and moving the electrodes while the electrodes and the dielectric body are placed in contact would not become a great defect. In those cases where the capacitance-phase conversion method is employed in the key operation speed detection device for an electronic musical instrument, the transmission electrode (or the reception electrode) is moved in accordance with the key operation and the reception electrode (or the transmission electrode) is arranged in a position that faces the transmission electrode (or the reception electrode). However, if the configuration is such that the electrodes are moved while the electrodes and the dielectric body are placed in strong contact, there is a possibility that the operational feeling of the keys would be affected by the friction resistance.