Voltage level detecting device, motor driving apparatus, motor driving system, and method for detecting voltage level

A voltage level detecting device is provided including comparators, a detection circuit, a trigger signal output circuit, a delayed control signal output circuit, a delayed comparison result signal output circuit, a circuit, and a control circuit. The comparators compare a voltage level of an input signal with each threshold level to generate and output a comparison result signal. The detection circuit detects a change in the comparison result signal and outputs a detection signal. The trigger signal output circuit outputs a trigger signal when a predetermined time has elapsed. The delayed control signal output circuit outputs a delayed control signal indicating a value of the control signal. The delayed comparison result signal output circuit outputs a delayed comparison result signal indicating the value of the comparison result signal. The circuit outputs a voltage level signal indicating a voltage level of the input signal. The control circuit outputs the control signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is based on and claims priority pursuant to 35 U.S.C. § 119(a) to Japanese Patent Application No. 2016-037767, filed on Feb. 29, 2016, in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein.

BACKGROUND

Technical Field

The present invention relates to a voltage level detecting device, a motor driving apparatus including the voltage level detecting device, a motor driving system including the voltage level detecting device, and a method for detecting a voltage level.

Description of the Related Art

There is a case where a mechanism is required for determining that continuous signals have reached a plurality of predetermined threshold voltage levels. For example, when a rotation position of a motor is controlled, such a mechanism determines that an input signal which changes according to a rotation phase of the motor has reached a threshold level provided for each predetermined phase, to detect a rotation phase of a rotor.

Specifically, as a method for detecting a rotation phase, one method is known in which a plurality of sensor signals (signals according to change of magnetic flux density) having a signal level according to the rotation position of the rotor of the motor is used to detect and output rotation phase information. In this method, the sensor signals are divided into a plurality of phase sections, and each divided sensor signal is compared with a threshold level provided for each predetermined phase, to detect that the sensor signal has reached the threshold level, thereby outputting a phase information signal indicating the detected phase.

SUMMARY

In accordance with some embodiments of the present invention, a voltage level detecting device is provided. The voltage level detecting device includes a plurality of comparators, a detection circuit, a trigger signal output circuit, a delayed control signal output circuit, a delayed comparison result signal output circuit, a circuit, and a control circuit. The plurality of comparators has a plurality of threshold levels different from each other based on a control signal, and compares a voltage level of an input signal to be changed with each threshold level to generate and output a comparison result signal indicating that the input signal has reached each threshold level. The detection circuit detects a change in the comparison result signal and outputs a detection signal. The trigger signal output circuit outputs a trigger signal when a predetermined time has elapsed after receiving the detection signal. The delayed control signal output circuit outputs a delayed control signal indicating a value of the control signal at the timing when the trigger signal has been received. The delayed comparison result signal output circuit outputs a delayed comparison result signal indicating the value of the comparison result signal at the timing when the trigger signal has been received. The circuit outputs a voltage level signal indicating a voltage level of the input signal based on the delayed control signal and the delayed comparison result signal. The control circuit outputs the control signal based on the voltage level signal and the comparison result signal.

In accordance with some embodiments of the present invention, the motor driving apparatus is provided. The motor driving apparatus includes the above level detecting device and an additional control circuit that drives and controls a motor based on a phase detecting information signal detected based on the voltage level signal.

In accordance with some embodiments of the present invention, a motor driving system is provided. The motor driving system includes the above motor driving apparatus and a motor to be driven and controlled by the additional control circuit.

In accordance with some embodiments of the present invention, a method for detecting a voltage level is provided. The method includes: comparing a voltage level of an input signal to be changed with each threshold level of a plurality of comparators having a plurality of threshold levels different from each other based on a control signal, to generate and output a comparison result signal indicating that the input signal has reached each threshold level; detecting a change in the comparison result signal to output a detection signal; outputting a trigger signal when a predetermined time has elapsed after receiving the detection signal; outputting a delayed control signal indicating a value of the control signal at the timing when the trigger signal has been received; outputting a delayed comparison result signal indicating the value of the comparison result signal at the timing when the trigger signal has been received; outputting a voltage level signal indicating a voltage level of the input signal based on the delayed control signal and the delayed comparison result signal; and outputting the control signal based on the voltage level signal and the comparison result signal.

DETAILED DESCRIPTION

Embodiments according to the present invention are described below referring to the drawings. The same component is denoted with the same reference numeral in the embodiments below.

A conventional voltage level detecting device had a disadvantage in that the voltage level detecting device causes a malfunction and the position becomes unknown when outputs of a plurality of comparators are changed in a short time interval, for example, in a case where a rotation speed of the motor becomes faster than a predetermined speed.

In view of this situation, a voltage detecting device is provided capable of accurately detecting a voltage level for detecting a phase with a simple configuration.

First Embodiment

FIG. 1is a schematic diagram of a general arrangement of an image forming apparatus200according to a first embodiment of the present invention. The general arrangement of the image forming apparatus200is described referring toFIG. 1. The image forming apparatus200is a tandem-type intermediate transfer system image forming apparatus using an electrophotographic system and is a full color copying machine.

InFIG. 1, the image forming apparatus200includes an image reading unit250, an image forming unit260, a paper feeding unit270, and a paper ejecting unit280. The image reading unit250is disposed above an apparatus body245and has a function for reading an image of a document. The image forming unit260is disposed below the image reading unit250. The image forming unit260has a function for forming an image on a paper sheet, as an example of a transfer material, based on image information (image data) read by the image reading unit250or transmitted from a personal computer that is an external device. The image forming unit260includes image forming devices. The paper feeding unit270is disposed at the lowest portion of the apparatus body245and has a function for supplying a paper sheet to a paper sheet conveyance path. The paper ejecting unit280is provided above the image forming unit260and has a function for ejecting the paper sheet on which the image has been formed.

The image reading unit250includes a contact glass, a light source, an image forming lens, an image sensor, and a plurality of mirrors.

The image forming unit260includes four image forming units201Y,201M,201C, and201Bk arranged from right to left inFIG. 1. The four image forming units201Y,201M,201C, and201Bk respectively correspond to four toner colors, i.e., yellow (Y), cyan (C), magenta (M) that are three primary colors of color materials, and black (Bk) that is an achromatic color. Each of the image forming units201Y,201M,201C, and201Bk functions as an image forming device and includes a combination of a plurality of components.

The four image forming units201Y,201M,201C, and201Bk have a common internal structure except for containing different color toners. Therefore, an outline of the image forming unit201Bk is described below as a representative to simplify the description. Regarding the other image forming units, the reference Bk attached to each member of the image forming unit201Bk is replaced with the reference Y for the image forming unit201Y, the reference M for the image forming unit201M, and the reference C for the image forming unit201C, and the descriptions on the other image forming units are omitted.

An optical writing unit206A is disposed above the four image forming units201Y,201M,201C, and201Bk. The optical writing unit206A writes a latent image to each photoconductor drum to be described. The image forming unit260includes a transfer unit207A that transfers toner images formed by the image forming units201Y,201M,201C, and201Bk onto an intermediate transfer belt207serving as an intermediate transfer body. The image forming unit260includes a secondary transfer unit210A that collectively transfers the toner images on the intermediate transfer belt207onto the paper sheet. The order of colors Y, M, C, and Bk is not limited to the arrangement illustrated inFIG. 1and may be another order. Each of the image forming units201Y,201M,201C, and201Bk may be a process cartridge that is attachable to and detachable from the apparatus body245.

The image forming unit201Bk includes a photoconductor drum202Bk serving as an image bearer, a charging roller203Bk, a developing device204Bk, and a cleaning device205Bk. The charging roller203Bk has a function as a charging device that uniformly charges an outer surface of the photoconductor drum202Bk. An exposure206Bk is a laser beam to form an electrostatic latent image on the outer surface of the photoconductor drum202Bk that has been uniformly charged. The developing device204Bk has a function as a developer that visualizes the electrostatic latent image formed on the photoconductor drum202Bk by the optical writing unit206A to a monochromatic toner image by using the toners of the corresponding colors. The cleaning device205Bk has a function as a cleaner that cleans and collects residual toner remaining on the outer surface of the photoconductor drum202Bk after transfer.

The photoconductor drum202Bk is rotary-driven clockwise inFIG. 1by a drum driving motor serving as a driver. The image forming units201Y,201M,201C, and201Bk are arranged in order at a predetermined pitch along a moving direction of the intermediate transfer belt207indicated by an arrow inFIG. 1with rotation axes of the photoconductor drums202Y,202M,202C, and202Bk being in parallel to each other.

The optical writing unit206A includes a light source such as a laser diode, a rotating polygon mirror for scanning, a polygon motor, and a scanning optical system such as a scanning lens (fθ lens). The optical writing unit206A scans and irradiates the outer surfaces of the photoconductor drums202Y,202M,202C, and202Bk with a laser beam to perform exposure based on image information input from the image reading unit250, a personal computer, or an external scanner. Accordingly, an electrostatic latent image corresponding to each color is formed on each of the photoconductor drums202Y,202M,202C, and202Bk.

The developing device204Bk is a two-component developing system developing device. The developing device204Bk includes a developer container that stores a developer including a black toner and a magnetic carrier. The developing device204Bk includes a developing roller204a, a screw that conveys and stirs the developer, and a toner concentration sensor. The developing roller204ais disposed opposed to the photoconductor drum202Bk and attaches the charged toner to the photoconductor drum202Bk. The developing roller204aincludes a rotatable sleeve on the outer side and a magnet secured to the inner side. A toner replenishing container212Bk is disposed above the developing device204Bk. The toner replenishing container212Bk communicates with the developing device204Bk to store the exchangeable toner and to supply the toner into the developing device204Bk. The toner replenishing container212Bk replenishes the toner in response to an output of the toner concentration sensor. Here, the toner replenishing container212Bk directly conveys the toner into the developer container. However, the toner replenishing container212Bk may include a replenishing path in the device body to replenish the toner into the developer container.

The cleaning device205Bk includes a cleaning blade205athat scrapes and removes residual toner and foreign substances attached to the outer surface of the photoconductor drum202Bk. The cleaning device205Bk further includes a storage container205bthat stores the removed residual toner and foreign substances. The residual toner and foreign substances removed by the cleaning blade205aand stored in the storage container205bare conveyed by a conveyance coil and a screw disposed in the storage container205bto be stored in a waste toner storing unit.

The transfer unit207A is an intermediate-transfer-system transfer device including the intermediate transfer belt207, two support rollers211aand211b, four primary transfer rollers208Y,208C,208M, and208Bk, and a secondary transfer roller210. The intermediate transfer belt207is disposed opposed to the photoconductor drums202Y,202M,202C, and202Bk. The intermediate transfer belt207is moved in a direction indicated by arrow inFIG. 1by a belt driving motor233illustrated inFIG. 2, serving as an intermediate transfer body drive unit to be described later. The intermediate transfer belt207is formed of an endless belt serving as an intermediate transfer body. The toner images formed on the photoconductor drums202Y,202M,202C, and202Bk are transferred onto the intermediate transfer belt207in an overlapping manner and conveyed thereby.

The two support rollers211aand211bsupport and stretch the intermediate transfer belt207(bridge the belt in tension-applied state) in a travelable and rotatable manner. The support roller211ais a driving roller coupled to the belt driving motor233illustrated inFIG. 2. The support roller211arotary-drives the intermediate transfer belt207in a direction indicated by arrow inFIG. 2. The support roller211bis a driven roller. The secondary transfer roller210is disposed at a position opposed to the support roller211aacross the intermediate transfer belt207. The secondary transfer unit210A indicates a device portion of the secondary transfer roller210disposed at a position opposed to the support roller211a, that is a driving roller, across the intermediate transfer belt207.

A belt cleaning device209is disposed above the intermediate transfer belt207near the support roller211a. The belt cleaning device209removes a residual toner component, an external additive component, or foreign substances attached to the outer surface of the intermediate transfer belt207. The belt cleaning device209includes a cleaning blade209adisposed in contact with the intermediate transfer belt207so as to face in the direction of movement of the intermediate transfer belt207. The belt cleaning device209also includes a metal cleaning counter roller209cdisposed opposed to the cleaning blade209aacross the intermediate transfer belt207. The residual toner component and the like removed by the cleaning blade209ais conveyed by a conveyance coil209band stored in the waste toner storing unit.

The primary transfer rollers208Y,208C,208M, and208Bk function as primary transfer units that respectively transfer the toner images from the photoconductor drums202Y,202M,202C, and202Bk onto the intermediate transfer belt207. The four primary transfer rollers208Y,208C,208M, and208Bk are respectively disposed opposed to the photoconductor drums202Y,202M,202C, and202Bk across the intermediate transfer belt207to form respective primary transfer nips serving as primary transfer units. The primary transfer rollers208Y,208C,208M, and208Bk each function as a contact transfer bias (transfer voltage) applying device and are coupled to a bias power source. The primary transfer rollers208Y,208C,208M, and208Bk can apply a primary transfer bias to the rear surface (inner surface) of the intermediate transfer belt207. The secondary transfer roller210is a driven roller energized by an energization unit to be pressed against the intermediate transfer belt207at the circumference of the support roller211a, thus forming a secondary transfer nip between the intermediate transfer belt207and the secondary transfer roller210. The secondary transfer roller210is a secondary transfer bias applying device to which a transfer bias having a polarity reverse to a polarity of the toner image to be transferred is applied. In this way, the secondary transfer roller210, forming the secondary transfer nip with the intermediate transfer belt207therebetween, provides a secondary transfer unit210athat collectively transfers the toner images on the intermediate transfer belt207onto the paper sheet. An image density sensor216is disposed near the intermediate transfer belt207above the support roller211b. The image density sensor216measures the amount and position of each color toner transferred onto the intermediate transfer belt207. The measured values are used for adjustment of image density and for positioning. The image density sensor216is of a combination of regular reflection and diffuse reflection.

A fixing unit213that heats a paper sheet P conveyed through a normal conveyance path229is disposed above the secondary transfer unit210A. The fixing unit213includes a fixing roller214and a pressurizing roller215that is opposed to and pressed against the fixing roller214. A heat source, such as a halogen heater, is disposed in the fixing roller214, and power is supplied from a power source to the halogen heater so that the temperature of the outer surface of the fixing roller214becomes a predetermined temperature. Heat and pressure are applied from the fixing roller214to the toner image on the paper sheet P in a fixing nip unit that is a pressing part between the fixing roller214and the pressurizing roller215so that the toner image is melted and fixed to the paper sheet P. The paper sheet P is conveyed from the fixing nip unit to a pair of conveying rollers.

The paper feeding unit270includes: paper feeding cassettes217aand217bthat store the paper sheets P and are drawable from the apparatus body245; a paper feeding roller218that presses the stored paper sheet P from above at a predetermined pressure to feed the paper sheet P; and a separation roller219that separates the fed paper sheet P one by one. A controller235controls a driving unit of the paper feeding unit270based on a signal instructed by an operation unit so that the paper feeding rollers218feed the paper sheets P stored in the paper feeding cassettes217aand217bto the normal conveyance path229. The paper feeding cassettes217aand217brespectively store paper sheets P having different sizes in the width direction that is perpendicular to the direction of conveyance of the sheet P. Hereinafter, for example, the description is made as assuming that A5 paper sheets P are stored in the paper feeding cassette217aand A4 paper sheets P are stored in the paper feeding cassette217b.The paper feeding unit270includes: a manual feed tray222on which a paper sheet to be fed, having an optional size within a predetermined range, is placed; and a paper feeding roller223that feeds the paper sheet. The paper feeding unit270rotary-drives the paper feeding roller223to feed the paper sheet placed on the manual feed tray222to the normal conveyance path229.

The paper ejecting unit280includes a first paper ejecting tray240and a pair of paper ejecting rollers224aand224b. The first paper ejecting tray240is formed on an inclined plane of the apparatus body245disposed below a paper ejecting space formed between the optical writing unit206A and the image reading unit250. The pair of paper ejecting rollers224aand224bejects the paper sheet, which has passed through the fixing unit213, from the normal conveyance path229to the first paper ejecting tray240. A second paper ejecting tray241and a pair of paper ejecting rollers225are disposed near and above the first paper ejecting tray240. The second paper ejecting tray241ejects the paper sheet on which an image has been formed by receiving a facsimile and is also used as a switchback conveying path to invert the paper sheet. The pair of paper ejecting rollers225ejects the paper sheet to the second paper ejecting tray241for ejecting the paper sheet. The pair of paper ejecting rollers225includes a driving roller and a driven roller and inverts a first surface of the paper sheet. The pair of paper ejecting rollers225is rotatable in both forward and reverse directions and is rotary-driven by a motor that is rotatable in both forward and reverse directions.

A switching claw226ais disposed in a branch between the normal conveyance path229and a paper ejecting path that is branched from the normal conveyance path229and extended to the pair of paper ejecting rollers224aand224b. Also, a switching claw226bis disposed above the switching claw226a,at a junction of the normal conveyance path229with a double-sided conveyance path230. The rocking positions of each top ends of the switching claws226aand226bcan be switched at a predetermined timing according to a printing mode, i.e., a one-sided printing mode or a double-sided printing mode, by a combination of a spring as an energization unit with a solenoid as a driving unit.

The apparatus body245includes the controller235that controls the image forming apparatus200and a temperature and humidity sensor242that detects the temperature and the relative humidity.

Next, conveyance paths and transfer devices for the paper sheet are described. The conveyance paths include the normal conveyance path229and the double-sided conveyance path230. The normal conveyance path229is a vertical-conveyance-type (vertical-path-type) conveyance path that conveys the paper sheets from the paper feeding unit270, disposed at a lower part of the apparatus body245, to the paper ejecting unit280, disposed at an upper part of the apparatus body245, in an upward direction. The double-sided conveyance path230inverts the paper sheet for double-sided printing. The conveyance paths229and230can be switched by the switching claw226b.The paper sheet, that has been guided to the double-sided conveyance path230by the switching claw226band conveyed to above the second paper ejecting tray241by the pair of paper ejecting rollers225, is inverted in a switchback manner as the pair of ejecting rollers225is rotated reversely.

Subsequently, the paper sheet is conveyed to the normal conveyance path229upstream from a pair of registration rollers221via the double-sided conveyance path230.

A plurality of pairs of conveying rollers220,228a,228b,and228cis disposed on the normal conveyance path229and the double-sided conveyance path230at intervals according to the minimum paper sheet size. These pairs of conveying rollers rotate to convey the paper sheet while sandwiching the paper sheet between the conveying rollers. The pair of registration rollers221is provided below the secondary transfer unit210a(secondary transfer nip) on the normal conveyance path229. The pair of registration rollers221adjusts a timing to convey the paper sheet to the secondary transfer unit210abased on a command from a controller.

FIG. 3is a block diagram of a structure of a motor driving apparatus101for the image forming apparatus200inFIG. 1. InFIG. 3, the motor driving apparatus101detects and outputs phase information of a motor M1based on sensor signals U1, V1, and W1. The sensor signals U1, V1, and W1are obtained as a signal amplifying circuit50in a sensor integrated circuit (IC) amplifies differential sensor signals (U1, U1-; V1, V1-; and W1, W1-) from magnetic sensors S1to S3(U-phase, V-phase, and W-phase) (referred to as sensor below) disposed around a rotor of the motor M1to detect an angle of rotation. The motor driving apparatus101includes a first phase detecting circuit10, a second phase detecting circuit120, a phase dividing circuit20, a signal selection circuit21, a third phase detecting circuit30, and a signal synthesizing circuit40.

InFIG. 3, the differential sensor signals (U1, U1-; V1, V1-; and W1, W1-) from the sensors S1to S3(U-phase, V-phase, and W-phase) are amplified by the signal amplifying circuit50including three amplifiers51to53and converted into single-ended signals. The converted signals are input to the first phase detecting circuit10, the second phase detecting circuit120, and the signal selection circuit21.FIG. 15is a table of a comparison result signal relative to the input signal to the first phase detecting circuit10inFIG. 3. The first phase detecting circuit10includes three comparators11to13. As illustrated inFIG. 15, the comparators11to13of the first phase detecting circuit10compare the amplitudes of the input differential sensor signals with a reference level Ref and respectively generate comparison result signals U2, V2, and W2having a Hi level or a Low level. Then, the comparators11to13output the comparison result signals U2, V2, and W2to the signal synthesizing circuit40. Here, the comparison result signals U2, V2, and W2from the first phase detecting circuit10become first phase information signals phA respectively having predetermined phases.

The second phase detecting circuit120includes three comparators121to123. As illustrated inFIG. 16, the comparators121to123generate comparison result signals U3, V3, and W3indicating a comparison result of two values and output the signals to the phase dividing circuit20and the signal synthesizing circuit40. Here, the comparison result signals U3, V3, and W3from the second phase detecting circuit120become second phase information signals phB respectively having predetermined phases.

The phase dividing circuit20generates a signal selection signal that has been divided into a section having a predetermined phase section based on the comparison result signals U3, V3, and W3and outputs the signal selection signal to the signal selection circuit21. Here, the sensor signals U1, V1, and W1are also input to the signal selection circuit21, and the signal selection circuit21selects an appropriate signal based on the signal selection signal from the phase dividing circuit20and outputs the selected signal to the third phase detecting circuit30as a selection signal X.

In addition, the third phase detecting circuit30primarily includes N−1 voltage sources32-1to32-(N−1) and N phase detectors31-1to31-N. The third phase detecting circuit30compares the selection signal X with a plurality of threshold levels generated by the N−1 voltage sources32-1to32-(N−1) and outputs a third phase information signal phC, indicating that the motor M1has been rotated at a predetermined angle, to the signal synthesizing circuit40. Subsequently, the signal synthesizing circuit40synthesizes the phase information signal phC with the first phase information signal phA and outputs the synthesized second phase information signal phB. The threshold levels are previously set according to signal amplitudes of the rotation angle sensors S1to S3.

FIG. 4is a timing chart of signals indicating operation states of the motor driving apparatus101inFIG. 3. InFIG. 4, the non-inverted signals U1, V1, and W1of the differential sensor signals from the sensors S1to S3are indicated by sine waves (instead of this, waveforms substantially similar to the sine wave may be used). The sensors S1to S3are arranged at intervals of 120 degrees of the electrical angle, and the inversion signals U1-, V1-, and W1- of the differential sensor signals form opposite phases of the respective sine waves.

The first phase detecting circuit10is used to obtain the comparison result signals U2, V2, and W2as a result of the comparison of the differential sensor signals (U1, U1-; V1, V1-; and W1, W1-) with the respective amplitude center level (common level). Also, the second phase detecting circuit120is used to obtain the comparison result signals U3, V3, and W3as a comparison result of the sensor signals U1, V1, and W1as illustrated inFIG. 16.

In addition, the phase dividing circuit20divides a phase into sections between switching edges of each comparison result signals U3, V3, and W3. For example, inFIG. 4, the phase dividing circuit20selectively switches and obtains the selection signal X in each divided phase section based on a table illustratedFIG. 17. InFIG. 4, each selection signal X is indicated by a thick line in the lower part ofFIG. 4. Each selection signal X is divided into sections of 60 degrees having high linearity, ranging from −30° to 30° or from 150° to 210° in terms of sine wave phase. That is, the divided phase section corresponds to the electrical angle of 60 degrees. In addition, horizontal arrows attached to the selection signal X inFIG. 4indicate the predetermined threshold levels. When the selection signal X reaches the predetermined threshold level, a pulse edge is output. For example, when a section between an electrical angle −30° and an electrical angle 30° of the selection signal X is divided into eight sections by 7.5°, a relation between the amplitude and the electrical angle is as indicated inFIG. 18. Here, it is assumed that the common level of the selected sensor signal be zero and the amplitude of the electrical angle 90° be one. As illustrated inFIG. 18, a predetermined threshold level is determined based on the ratio of the selection signal X relative to the sine wave amplitude. When the electrical angle is −30° and 30°, the second phase information signal phB is available. When the electrical angle is 0°, the first phase information signal phA is available. Therefore, the above electrical angles are not necessarily used as the predetermined threshold level of the third phase detecting circuit30.

FIG. 7Ais a circuit diagram of a structure of a phase detecting circuit30-1according to an example 1 of the third phase detecting circuit30inFIGS. 3, 5A, and 5B. InFIG. 7A, the phase detecting circuit30-1includes three voltage sources43to45,2N resistances47-N to47-1and48-1to48-N coupled to each other in series, and2N comparators41-N to41-1and42-1to42-N. The phase detecting circuit30-1compares the signal amplitude of the selection signal X with a plurality of threshold levels to generate and output a phase detecting signal phC (ph (N)− to ph (1)− and ph (1)+ to ph (N)+). InFIG. 7A, a voltage VR1level of the voltage source44is an amplitude center (common) level of the sine wave. A voltage VR2level and a voltage VR0level of the voltage sources45and43respectively correspond to the upper limit level and the lower limit level of the sine wave amplitude. A level at which the voltage is divided at an amplitude ratio interval according to the electrical angle with the voltage VR1level as the center is compares with the selection signal X. The selection signal X simply increases or decreases so that the phase detecting signal phC is switched to be output in order.

Subsequently, the signal synthesizing circuit40synthesizes the first phase information signal phA, the second phase information signal phB, and the third phase information signal phC to generate at least one digital signal and output the digital signal as a motor control signal.

As described above, according to the present embodiment, with the signal which is output each time when the selection signal X reaches the amplitude level according to the electrical angle, the phase data more than the number of the phase information signals obtained by the first phase information signal phA can be obtained. InFIG. 18, a method for obtaining the phase information by the electrical angle of 7.5° is illustrated as an example. As another example, when the amplitude ratio is divided by the electrical angle of 6°, the phase information twice as much as the phase information of a case of the electrical angle of 6° is obtained, and when the amplitude ratio is divided by the electrical angle of 3°, the phase information of two and half times of a case of the electrical angle of 7.5° is obtained.

InFIG. 4, the selection signal X exists in the section between the sine wave of −30° and 30° of each sensor signal or the section between 150° and 210°. Even when the phase section is switched and the selected sensor signal is changed, the selection signal X is continuously kept. Since a signal next to the third phase information signal phC which is the comparison result signal from the third phase detecting circuit30illustrated inFIG. 7Ais switched in order, the final synthesis signal can form a gray code.

Second Embodiment

FIG. 5Ais a block diagram of a structure of a motor driving apparatus102for an image forming apparatus200inFIG. 1according to a second embodiment of the present invention. The motor driving apparatus102according to the second embodiment is different from the motor driving apparatus101according to the first embodiment in that a signal amplifying circuit50is not provided. That is, a sensor signal remains as a differential signal, not a single-ended signal, and differential sensor signals (U1, U1-; V1, V1-; and W1, W1-) from sensors S1to S3(U-phase, V-phase, and W-phase) are output and are respectively input to a first phase detecting circuit10, a second phase detecting circuit120, and a signal selection circuit21. Here, in the first phase detecting circuit10, the sensor signals U1and U1- are input to a comparator11, and the sensor signals V1and V1- are input to a comparator12, and the sensor signals W1and W1- are input to a comparator13. Then, phases of the sensor signals are detected. In the second phase detecting circuit120, a comparison result of the sensor signals are obtained. Therefore, it is not necessary to input the differential signal, and a one-side signal of each differential sensor signal may be input.

FIG. 5Bis a block diagram of a structure of a motor driving apparatus102A for the image forming apparatus200inFIG. 1according to a modification of the second embodiment of the present invention. The motor driving apparatus102A according to the modification of the second embodiment is different from the motor driving apparatus102according to the second embodiment in that the motor driving apparatus102A includes a signal amplifying circuit50aincluding amplifiers51a,52a,and53ahaving input and output signals which are differential signals at output ends of the sensors S1to S3. The differential sensor signals (U1, U1-; V1, V1-; and W1, W1-) from the sensors S1to S3(U-phase, V-phase, and W-phase) are once amplified by the signal amplifying circuit50ato obtain the differential sensor signals (U1, U1-; V1, V1-; and W1, W1-). Then, the differential sensor signals (U1, U1-; V1, V1-; and W1, W1-) are respectively input to the first phase detecting circuit10, the second phase detecting circuit120, and the signal selection circuit21. Although the second embodiment and the modification have the same effect, the signal amplifying circuit50ais easily used in a point that the signal amplifying circuit50auniformizes the sensor signals.

Here, a role of the signal amplifying circuit50ais described below. The common level and amplitude level of the differential sensor signals from the sensors S1to S3(U-phase, V-phase, and W-phase) are often not uniformed. Also, the amplitude level is often electrically very small. When the levels are uniformed and the amplitude is larger, the output signal which has aimed a predetermined rotation angle from the third phase detecting circuit30indicates a value closer to the actual rotation angle of a rotor. That is, the purpose is to adjust the common level and to adjust and amplify the amplitude level by the signal amplifying circuit50awhen the differential sensor signals from the sensors S1to S3are not uniform.

Therefore, an operation of the modification of the second embodiment inFIG. 5Bwhich is easily used is mainly described below. As described above, the amplified differential sensor signals (U1, U1-; V1, V1-; and W1, W1-) have been input to the first phase detecting circuit10, the second phase detecting circuit120, and the signal selection circuit21. As illustrated inFIG. 19, for example, the first phase detecting circuit10outputs comparison result signals U2, V2, and W2having a high level or a low level according to an input condition. The comparison result signals U2, V2, and W2from the first phase detecting circuit10become first phase information signals phA which respectively have predetermined phases to be output to a signal synthesizing circuit40. Also, the second phase detecting circuit120outputs the input sensor signals U1, V1, and W1as the comparison result signals U3, V3, and W3having two values, for example, as illustrated inFIG. 16. The comparison result signals U3, V3, and W3from the second phase detecting circuit120become second phase information signals phB respectively having predetermined phases.

The comparison result signals U2, V2, and W2and the comparison result signals U3, V3, and W3are also input to the phase dividing circuit20. The phase dividing circuit20outputs a signal obtained by dividing each input signal into sections having predetermined phase sections to the signal selection circuit21. The differential sensor signals U1, U1-, V1, V1-, W1, and W1- are also input to the signal selection circuit21. A predetermined appropriate signal is selected based on an output signal from the phase dividing circuit20as described in detail below. Subsequently, the selection signal X from the signal selection circuit21is input to the third phase detecting circuit30, and the selection signal X reaches a predetermined threshold level in the third phase detecting circuit30. Accordingly, a plurality of phase detecting signals output as phase information for informing that the motor has rotated at a predetermined angle is output to the signal synthesizing circuit40as the third phase information signal phC. The signal synthesizing circuit40synthesizes the first phase information signal phA, the second phase information signal phB, and the third phase information signal phC to obtain a synthesized phase information signal Phsyn having more phase information than the first phase information signal phA and use the above signal as a motor drive controlling signal. Here, the predetermined threshold level indicates a level according to a signal amplitude of each of the rotation angle sensors S1to S3, and the predetermined threshold level is previously set.

FIG. 6is a timing chart of signals indicating operation states of the motor driving apparatuses102and102A inFIGS. 5A and 5B. The differential sensor signals (U1, U1-; V1, V1-; and W1, W1-) are signals from the sensors S1to S3arranged around the rotor of the motor M1at electrical angle 120° intervals. Each signal is output as having a phase which is 120° different from the sine wave according to the magnetic flux density of the rotor. Here, in the first phase detecting circuit10, (1) the comparison result signal U2is obtained as a comparison result of the sensor signals U1and U1-, (2) the comparison result signal V2is obtained as a comparison result of the sensor signals V1and V1-, and (3) the comparison result signal W2is obtained as a comparison result of the sensor signals W1and W1-. In addition, the second phase detecting circuit120compares the signals as illustrated inFIG. 16based on the sensor signals U1, V1, and W1to obtain the comparison result signals U3, V3, and W3. The second phase detecting circuit120can obtain the similar comparison result signals U3, V3, and W3with comparison based on the sensor signals U1-, V1-, and W1-. The second phase detecting circuit120divides a phase in a section between a switching edge and an edge of each comparison result signals U2, V2, and W2and comparison result signals U3, V3, and W3. In the predetermined phase dividing section, the second phase detecting circuit120selectively switches the selection signal X according to the input condition inFIG. 20and generates it, for example, inFIG. 7A. Therefore, the continuous selection signal X can be obtained at a dividing section boundary when the dividing phase is 30 degrees of the electrical angle. In a section between 150 and 180 degrees and a section between zero and 30 degrees of the sine wave, the linearity is very high, and the third phase detecting circuit30advantageously detects the phase level.

FIG. 7Bis a circuit diagram of a structure of a phase detecting circuit30-2according to an example 2 of the third phase detecting circuit30inFIGS. 3, 5A, and 5B. In comparison with the phase detecting circuit30-1inFIG. 5Aaccording to the example 1, the phase detecting circuit30-2according to the example 2 does not include a circuit lower than the voltage source44and the comparator42-1. According to the example 2, as illustrated inFIG. 5B, even when the predetermined threshold level of the second phase detecting circuit30-2becomes a half, the effect similar to the effect of the phase detecting circuit30-1according to the example 1 is obtained, and the sizes of the motor driving apparatuses102and102A can be reduced.

Subsequently, an exemplary signal synthesizing circuit40is described below which synthesizes the phase information signal phC from the third phase detecting circuit30with the phase information signals phA and phB respectively from the first phase detecting circuit10and the second phase detecting circuit120and outputs a two-phase digital signal.

FIG. 8is a timing chart of signals indicating operations of the third phase detecting circuit30inFIGS. 3, 5A, and 5B. InFIG. 8, the selection signal X inFIG. 4is indicated. Also, the third phase information signals phC from the third phase detecting circuit30having predetermined threshold levels LV (1) to LV (4) obtained by dividing a section of electrical angle 30° into five sections are indicated as phase information signals ph (1) to ph (4). The signal synthesizing circuit40outputs two kinds of output digital signals OUT1and OUT2. The signal synthesizing circuit40synthesizes the phase information signals ph (1) and ph (3) with the comparison result signals U3, V3, and W3and outputs the synthesis signal as the output digital signal OUT1. Subsequently, the signal synthesizing circuit40synthesizes the phase information signals ph (2) and ph (4) with the comparison result signals U2, V2, and W2and outputs the synthesis signal as the output digital signal OUT2. Accordingly, an encoder signal having a period with ¼ phase difference can be easily obtained without including an optical encoder.

Third Embodiment

FIG. 9is a block diagram of a structure of a motor driving apparatus (motor driving system)103for the image forming apparatus200inFIG. 1according to a third embodiment of the present invention. As illustrated inFIG. 9, in comparison with the motor driving apparatus102A according to the modification of the second embodiment inFIG. 5B, the motor driving apparatus103includes (1) a motor driving unit70which selectively supplies a driving current to a plurality of motor coils to rotate and drive a rotor of a motor M1and (2) a motor controller60which generates a PWM signal based on a second phase information signal phB and outputs the PWM signal to the motor driving unit70. Other components are the same as the components of the modification of the second embodiment, and the description of the other components is omitted.

FIG. 10is a circuit diagram of a structure of the motor driving unit70inFIG. 9. InFIG. 10, the motor driving unit70includes a predriver80and a driver90. For example, it is assumed that a three-phase coil to drive the motor M1which is a brushless DC motor have three phases, i.e., a U-phase, a V-phase, and a W-phase, and the coils form an Y connection in the motor M1. The main driver90includes high-side switch elements91,93, and95coupled to a side of a power source of the other ends of the coils and low-side switches92,94, and96coupled to a side of the ground. The predriver80outputs switch control signals UH, UL, VH, VL, WH, and WL to respectively drive the switch elements91to96having each phase. The predriver80includes a driving phase controller81and three drive amplifiers82to84. The switch control signals UH, UL, VH, VL, WH, and WL are formed in pairs, and the driving phase controller81sorts the phases into the following states, i.e., a phase in which a synchronous rectification operation is performed at a PWM duty cycle, a phase in which the low-side is turned off, a phase in which both the high and low sides are turned off. The switch control signals UH, UL, VH, VL, WH, and WL drive the synchronous rectification phase according to the PWM signal with the duty cycle determined by the motor controller60. Here, the phases are sorted into the states, that is, the state of the PWM synchronous rectification drive, the state in which the low side is turned on, and the state in which both sides are turned off. The motor M1is rotated and driven by determining the phases according to the signal logics of the phase information signals U2, V2, and W2generated based on the sensor signals respectively from the magnetic sensors Si to S3to obtain position information arranged near the rotor of the motor M1.

FIG. 11is a timing chart of signals indicating operations of the motor driving unit70inFIG. 10. InFIG. 11, an example of state switching of the signal logic of the sensor signals having the respective phases is illustrated, and this example is a general driving method as a method for driving the brushless DC motor.

The motor controller60appropriately controls the duty cycle of the PWM signal based on the phase and position information on the rotating motor M1which is accurate as possible and outputs the PWM signal to the motor driving unit70. A drive control voltage may be input to the motor driving unit70instead of the PWM signal without providing the motor controller60, and in the motor driving unit70, the input drive control voltage may be compared with a triangular wave having a constant frame period to generate a PWM signal.

The sensors S1to S3for phase switching to drive the brushless motor and the plurality of sensors having the phase information described in the first embodiment and the second embodiment are used in common. This is the feature of the motor driving apparatus103inFIG. 9. In addition, the first phase detecting circuit10is also used in common. That is, since the sensor signal which has been traditionally used is used, much phase information can be obtained without providing an additional sensor.

Fourth Embodiment

FIG. 12is a block diagram of a structure of a third phase detecting circuit (referred to as a phase detecting circuit below)30A including a voltage level detecting device according to a fourth embodiment of the present invention.FIG. 13is a timing chart of an operation of the phase detecting circuit30A inFIG. 12.FIG. 14Ais a graph of input output characteristics of hysteresis comparators (referred to as comparator below)311and312inFIG. 12.FIG. 14Bis a truth table of an operation of a logical circuit316inFIG. 12. InFIG. 14B, the number “0x” indicates a hexadecimal digit.FIG. 14Cis a graph of a selection signal in a case where a signal D [29:1] of the phase detecting circuit30A inFIG. 12is simplified as signal voltages D19to D1.FIG. 14Dis another timing chart of an operation of the phase detecting circuit30A inFIG. 12. The structure, operation, and effect of the phase detecting circuit30A inFIG. 12are described below referring toFIGS. 12 to 14D.

InFIG. 12, the phase detecting circuit30A is a modification of the phase detecting circuits30for the motor driving apparatuses101,102,102A, and103. For example, the phase detecting circuit30A is provided to detect a rotation phase of a rotor of a motor M1of an image forming apparatus200. In particular, the phase detecting circuit30A includes the two comparators311and312. Each of the comparators311and312compares the signal selection signal X, which indicates the rotation phase of the motor from the signal selection circuit21inFIG. 3and continuously changes, with a reference voltage (threshold level). The reference voltage of the comparator311is different from the reference voltage of the comparator312. The reference voltages (threshold level) of the comparators311and312are switched based on a change signal indicating a change of the output signals from the comparators311and312, and a control signal DA_SW [29:1] of the reference voltage is latched with a delayed signal. In the present embodiment, for example, phase detecting information signals ENCA and ENCB can be generated without the first phase detecting circuit10and the signal synthesizing circuit40inFIG. 3. In comparison with the first embodiment and the like, the circuit structure can be simplified. In addition, a motor phase can be accurately detected.

InFIG. 12, the phase detecting circuit30A includes an analog circuit401and a digital circuit402. The analog circuit401includes the comparators311and312, a delay circuit (trigger signal output unit)321, a reference voltage source322, for example, 30 resistances R, and, for example, 29 switches SW1to SW29. The digital circuit402includes a control circuit (controller)310, a control circuit (detector)320, delay flip-flops (delayed comparison result signal output unit)313and314, delay flip-flops (delayed control signal output unit)315-1to315-29, the logical circuit316, and an operation circuit317.

In the analog circuit401, for example, the 29 voltages D1to D29are generated by using the 30 resistances R based on a reference voltage Vda of the reference voltage source322. The voltages D1, D3, . . . , D29having odd numbers are input to a non-inverted input terminal of the comparator311as reference voltages DAA respectively via the switches SW1, SW3, . . . , SW29. The voltages D2, D4, . . . , D28having even numbers are input to a non-inverted input terminal of the comparator312as reference voltages DAB respectively via the switches SW2, SW4, . . . , SW28. For example, the selection signal X from the signal selection circuit21inFIG. 3is input to each inverted input terminal of the comparators311and312. The comparators311and312have a threshold Vth from the L level to the H level and a threshold Vth-Va from the H level to the L level and have hysteresis characteristics having a hysteresis delay time th. The two switches next to each other are turned on from among the switches SW1to SW29based on the control signal DA_SW [29:1] from the control circuit310.

In the digital circuit402inFIG. 12, the flip-flop313outputs a comparison result signal SLICE_A upon the reception of a trigger pulse signal DA_SW PLUS_D (trigger signal) from the delay circuit321as a signal A. The flip-flop314outputs a comparison result signal SLICE_B upon the reception of the trigger pulse signal DA_SW_PLUS_D (trigger signal) from the delay circuit321as a signal B. The flip-flops315-1to315-29output the control signal DA_SW [29:1] upon the reception of the trigger pulse signal DA_SW_PLUS_D (trigger signal) from the delay circuit321as a signal C.

The logical circuit316performs a logical operation with reference of the truth table inFIG. 14Bbased on the input signals A, B, and C and outputs a signal D which is the operation result to the control circuit310and the operation circuit317. The comparison result signals and the signals A to D indicate as follows. (1) The comparison result signal SLICE_A indicates a comparison result of the selection signal X with the reference voltage DAA from one of the switches SW1, SW3, . . . , SW29having odd numbers. (2) The comparison result signal SLICE_B indicates a comparison result of the selection signal X with the reference voltage DAB from one of the switches SW2, SW4, . . . , SW28having even numbers. The reference voltages DAA and DAB are fixed values of the level of the signals D1to D29inFIG. 12, for example. The signals SLICE_A and SLICE_B which have respectively selected the reference voltages DAA and DAB are sequentially changed. (3) The signal A indicates the comparison result signal SLICE_A (delayed comparison result signal) upon the reception of the trigger pulse signal DA_SW_PLUS_D from the delay circuit321. (4) The signal B indicates the comparison result signal SLICE_B (delayed comparison result signal) upon the reception of the trigger pulse signal DA_SW_PLUS_D from the delay circuit321. (5) The signal C is a signal (delayed control signal) indicating the states of the switches SW1to SW29. When the bit is one, the corresponding switch is turned on, and when the bit is zero, the corresponding switch is turned off. The two switches next to each other from among the 29 switches SW1to SW29are turned on. (6) For example, when the level of the selection signal is between the signal D4and the signal D3, the signal D indicates a comparison result of the signals D29to D1with the selection signal by a bit string. Since the signals D29to D4are all “zero” and the signals D3to D1are all “one”, the bit string expressed as binary numbers is “0000000000_0000000000_000000111b”, and the bit string expressed as decimal numbers is “seven”.

The operation of the logical circuit316is described below. As described above, two switches from among the switches SW1to SW29next to each other are turned on. In this case, three states may occur, i.e., a state301in which the voltage of the selection signal X is lower than the voltages of the two switches (referred to as two voltages below), a state302in which the voltage of the selection signal X is between the two voltages, and a state303in which the voltage of the selection signal X is higher than the two voltages (refer toFIG. 14B). An example of a logic calculation is described below. (1) For example, when the switches SW1and SW2are turned on and the state is the state301in which the voltage of the selection signal X is lower than the two voltages, the signals A and B are zero. The logical circuit316encodes the signal C=0x0000_0003, the signal A=0, and B=0 and outputs the output signal D=0x0000_0000 (state306inFIG. 13). (2) For example, when the switches SW1and SW2are turned on and the state is the state302in which the voltage of the selection signal X is between the two voltages, the signal A=1 and the signal B=0 are satisfied. The logical circuit316encodes the signal C=0x0000_0003 and A=1, B=0 and outputs the output signal D=0x0000_0001 (state305inFIG. 13). (3) For example, when the switches SW1and SW2are turned on and the state is the state303in which the voltage of the selection signal X is higher than the two voltages, the signal A=1 and the signal B=1 are satisfied. The logical circuit316encodes the signal C=0x0000_0003 and A=1, B=1 and outputs the output signal D=0x0000_0003 (state306inFIG. 13).

The operation circuit317performs a calculation on the output signal D to be input by using the following formulas (1) to (3) and generates and outputs the phase information signals ENCA and ENCB (corresponding to synthesized two-phase encoder signal inFIG. 8).
ENCA=(D[1]^D[3])|(D[5]^D[7])|(D[9]^D[11]|(D[13]^D[15])|(D[17]^D[19])|(D[21]^D[23])|(D[25]^D[27])|D[29]  (1)

Here, the reference ^ indicates an EXOR operation for each bit, and the reference | indicates the division of the bit.

InFIG. 14C, the selection signal in a case where the signal D[29:1] of the phase detecting circuit30A inFIG. 12is simplified as signal voltages D19to D1is illustrated.

The control circuit310generates a 30-bit control signal DA_SW [29:1] which turns of the two switches next to each other from among the switches SW1to SW29based on the comparison result signals SLICE_A, SLICE_B, and D. The control signal DA_SW [29:1] is output to the control circuits310and320, the flip-flops315-1to315-29, and the switches SW1to SW29. Specifically, the control circuit310operates the switches SW1to SW29so that one of the comparison result signals SLICE_A and SLICE_B becomes zero and the other signal becomes one. For example, when (SLICE_A, SLICE_B)=(0, 1) is changed to (SLICE_A, SLICE_B)=(0, 0) in a state where the switches SW2and SW3are turned on, the control circuit310turns off the switch SW3and turns on the switch SW1(state307inFIG. 13). That is, in the bit string of the signals D29to D1, all higher-order bits than the voltage level of the selection signal are “zero”, and all lower-order bits than the voltage level of the selection signal are “one”. The control circuit310changes the signal DA SW near the boundary between zero and one of the bit string of the signal D to “one” (=turn on) based on the changes of the comparison result signals SLICE_A and SLICE_B.

When the states of the comparison result signals SLICE_A and SLICE_B and the control signal DA_SW [29:1] are changed, the control circuits320generates an H-level one-shot pulse signal DA_SW_PLUS (detection signal) and outputs the signal to the delay circuit321. The delay circuit321delays the input one-shot pulse signal DA_SW_PLUS by a predetermined delay time Td2and generates the delayed trigger pulse signal DA_SW_PLUS_D. Then, the delay circuit321outputs the delayed trigger pulse signal to the flip-flops313,314, and315-1to315-30. Here, for example, the delay time Td2is set to be two μs which is obtained by adding a switching time of the switches SW1to SW29, operation delay times of the comparators311and312, and an operation delay time. InFIG. 13, for example, a delay time Td1is set to be one μs which is obtained by adding the delay times of the comparators311and312and the output delay time. In this embodiment, the maximum value of an interval Tp is 5.5

The phase detecting circuit30A formed as described above divides the phase section into30sections and detects the levels of 29 boundaries between the sections. When the comparison result of the comparison result signals SLICE_A and SLICE_B has been changed, the control circuit320detects the change and latches the states of the switches SW1to SW29to be the output signal D [29:1] with a signal obtained by delaying the timing of the detection result by the delay circuit321as a trigger. The operation circuit317encodes the output signal D [29:1] as described above and generates and outputs the phase detecting information signals ENCA and ENCB indicating phase positions.

An example of a specific operation is described referring to the timing chart inFIG. 13. When the voltage of the selection signal X is between the voltages D5and D4, the non-inverted input terminal of the comparator311for outputting the comparison result signal SLICE_A which is the comparison result is coupled to the voltage D5of the switch SW5, and the comparison result signal SLICE_A becomes the L level (0). Also, the non-inverted input terminal of the comparator312for outputting the comparison result signal SLICE_B which is the comparison result is coupled to the voltage D4of the switch SW4, and the comparison result signal SLICE_B becomes the H level (1). When the voltage of the selection signal X falls below the voltage D28, the comparison result signal SLICE_B becomes the L level (0), and the comparison reference voltage of the comparator311is switched from the voltage D5to the voltage D3with the change of the voltage as a trigger. The flip-flops315-1to315-30latch the states of the switches SW1to SW29with the signal DA_SW_PLUS_D which is obtained by delaying the trigger, and the logical circuit316encodes the signals to output the signal D[29:1].

According to the phase detecting circuit30A described above, from the change of the comparison result signal SLICE_A or the comparison result signal SLICE_B to the change of the encode level of the logical circuit316via the delay circuit321, the switches of the comparison result signals SLICE_A and SLICE_B are not changed. Accordingly, when the signal is changed within a predetermined time due to a sudden change of the selection signal X, changes sequentially occur. Therefore, a change equal to or less than the delay time of the delay circuit321does not occur in the phase detecting information signals ENCA and ENCB which are encode output signals. In the present embodiment, for example, without providing the first phase detecting circuit10and the signal synthesizing circuit40inFIG. 3, the phase detecting information signals ENCA and ENCB can be generated. Therefore, in comparison with the first embodiment and the like, the circuit structure can be simplified. In addition, a motor phase can be accurately detected.

The phase detecting circuit30A can asynchronously detect the motor phase by using two thresholds DAA and DAB which dynamically changes due to the change of the selection signal X without using a clock as described above. In comparison with the first embodiment and the like, the circuit structure of the phase detecting circuit30A can be simplified. In addition, the phase detecting circuit30A can accurately detect a motor phase. For example, inFIG. 13, the inclination of the selection signal X is changed according to the rotation speed of the motor. Therefore, it can be understood that an interval Tp between vertical lines become wider when the motor speed becomes lower. The interval Tp inFIG. 13is similar to the interval between the vertical lines inFIGS. 14C and 14D. However, the interval between the vertical lines is Tp/2 inFIGS. 14C and 14D.

The output signal D[29:1] is expressed by the gray code in the truth table inFIG. 14B. The output signal D[29:1] is set so as to increase to apply one from the lower bit to the upper bit from the states of Nos. 1 to 3 in which the level is low to the state in which the level is high. The gray code in the present embodiment is not technically the same as a gray code of a gray code counter. Here, the gray code means that a one-bit change occurs at a change point. Since the change of one bit occurs at the change point, generation of an unnecessary glitch can be prevented when the operation circuit317encodes the phase detecting information signals ENCA and ENCB. Here, the glitch or a glitch noise means a whisker-like pulse generated in the output signal due to a difference between signal delay times when the signals are input at times close to each other.

As described above, according to the present embodiment, even when the number of the threshold levels is increased to more accurately detect a phase, a motor phase detector can be configured by using the two comparators311and312. After the output changes of the comparators311and312cause a change signal and the change signal switches the comparison level, the output changes of the comparators311and312are latched with the signal which is obtained by delaying the comparison level switching signal. Therefore, the selection signal X can be input without considering a settling time. Therefore, according to the present embodiment, a voltage level detecting device can be provided which can detect the voltage level to more accurately detect the phase with more simple structure compared with a traditional phase detecting circuit.

The sensors S1to S3according to the present embodiment are magnetic sensors to detect the rotor of the motor M1, and a hall element is used as the sensors in general. There are many cases where the magnetic flux density generated by the rotation of the rotor is a sine wave. That is, the signal from the magnetic sensor is a sine wave in many cases. However, the magnetic flux density generated by the rotation of the rotor and received by the fixed magnetic sensor is not always a well-shaped sine wave and may be a distorted sine wave. Also, there is a case where a magnetic sensor output is saturated and forms a shape like a trapezoidal wave due to a magnetic saturation. The sensed magnetic flux density exceeds an allowable value of the magnetic sensor, and this causes the magnetic saturation. However, when the signal has a waveform of the sine wave or a wave form close to the sine wave in the section of electrical angle of −60° to 60°, a plurality of phases can be accurately detected according to the present invention.

In the above embodiments, the sensor signal may be also used as a sensor signal from a sensor for switching a commutation current of a plurality of coils of a motor current driving device.

In the above embodiments, the hysteresis comparators311and312are used. However, the present invention is not limited to this and may include a comparison units such as a comparator which does not have hysteresis characteristics.

In the above embodiments, the phase detecting circuit30A includes the two comparators311and312which compare the signal selection signal X indicating the rotation phase of the motor from the signal selection circuit21inFIG. 3and the like and continuously changes with the reference voltages (threshold) different from each other. However, the present invention is not limited to this, and it is preferable that the selection signal X indicate a predetermined signal phase.

In the above embodiments, the flip-flop313,314, and315-1to315-30are included. However, the present invention is not limited to the above structure, and it is preferable to include a storage unit which temporality stores or latches the input signal.

In addition to the above embodiments, a motor driving system according to the present invention may be used for a motor for driving a conveying roller in a sheet-shaped prepreg as a conveying device and a device for conveying a paper money.