Motor drive device

A motor drive device for alternately driving a plurality of motors includes a position detection signal processing circuit for processing position detection signals of the plurality of motors, a pre-drive circuit for generating an excitation switching signal of the motors, a plurality of power switching circuits for supplying an electric current to the motors in response to an output from the pre-drive circuit, and a motor switching circuit for instructing a switchover of driving the motors. The position detection signal processing circuit, in response to an input signal to the motor switching circuit, selects a position detection signal of a motor to be driven out of the position detection signals of the plurality of motors, and inputs a position detection processed signal to the pre-drive circuit for selecting one of the plurality of power switching circuits.

TECHNICAL FIELD

The present invention relates to a motor drive device alternately driving a plurality of motors used in an apparatus.

BACKGROUND ART

In recent years, a number of motors have been often used in an individual audio & video apparatus or an individual office automation apparatus. Some home appliances such as a dishwasher or a washing and drying machine also employs a plurality of motors.

Each one of the motors has been provided with a driving circuit and a control circuit so that the plurality of motors can be driven or controlled. The entire circuit thus becomes complicated, which prevents the apparatuses from being downsized or less expensive. To overcome this problem, it has been proposed that a plurality of driving circuits is integrated into one chip IC. This proposal is disclosed in, e.g. Japanese Patent No. 2662397.

The technique disclosed in this patent publication is this: A constant-current driving element, which incurs a greater loss among others, is disposed outside an IC chip so that an obstruction to integrating a plurality of driving circuits into one chip can be lessened, where the obstruction is an increase in heat generated due to greater loss in the IC chip.

FIG. 7shows the related art disclosed in the foregoing patent publication. InFIG. 7, driving control IC401is formed of one chip containing a plurality of push-pull driving block402, constant-current driving circuit block403, and power-supply control block404.

Push-pull driving block402outputs a bipolar output voltage, in response to a signal supplied to its input terminal, to DC motors M1and M2disposed outside of IC401via the IC's output terminals +OUT and −OUT. Constant-current driving circuit block403drives, in a constant-current manner, a load coupled to the output terminal in response to the signal supplied to the input terminal. An output from constant-current driving circuit block403drives, in a constant-current manner, solenoid S working as a plunger via driving transistor Tr1externally coupled to driver IC401. The foregoing structure allows lessening the loss inside the IC and achieving an integration of multiple driving control blocks into one chip IC.

Unexamined Japanese Patent Publication No. 2003-202719 discloses another technique independent of the forgoing technique disclosed in the patent publication. This one refers to a driving device which independently drives a plurality of DC brush-less motors so that a plurality of photosensitive drums of a tandem multi-color image-forming apparatus can be rotated. This invention proposes a technique of integrating the driving circuits of respective brush-less motors into one unit.

This technique allows sharing a part of functions except a switching section with the shafts of the plurality of motors, each one of which motors independently drives a plurality of photosensitive drums, and allows integrating the part of the functions into one chip for downsizing the motor and reducing the cost thereof. This switching section varies the outputs of the motors by switching over exciting coils.

A circuit operation of a conventional driving device of the motors disclosed in this publication is described hereinafter with reference toFIGS. 8 and 9.FIG. 8shows a conventional circuit structure of this related art.FIG. 9shows an internal structure of a conventional driving section.

The driving device shown inFIG. 8drives and controls the objectives to be driven of the image forming apparatus, and is formed of driver505, image-forming circuit drive device500, and other motors503,504. Circuit drive device500is formed of four rotation drive devices. Each one of the rotation drive devices works as a driving source which supplies torque to each one of photosensitive drums502A,502B,502C and502D for driving those drums. The respective rotation drive devices are formed of sensor-less DC brushless motors501A,501B,501C and501D respectively, and speed reduction mechanisms corresponding to those sensor-less DC brushless motors, and encoders also corresponding to those motors.

Driver505receives a signal from the encoder for driving DC brushless motors501A,501B,50C and501D, and also drives other motors503and504. This driver505is generally formed of various ICs mounted on a sheet of printed circuit board.

FIG. 9shows an internal structure of driver505shown inFIG. 8. Driver505is formed of driving circuit508, control IC509, and back-electromotive voltage detecting circuit510. Circuit510detects a back-electromotive voltage induced at each one of the phases of stator wirings of DC brushless motor501A having a three-phase connection, and outputs the detection signal to driver IC506. Driving circuit508is formed of one driver IC506and switching section (switching element)507responsive to the four shafts of the motors.

Driving circuit508receives a speed control signal from control IC509, and then supplies a three-phase voltage driving signal to respective DC brushless motors501A,501B,501C and501D. As discussed above, at least a part of the functions except switching section507of driving circuit508is integrated into one chip, and this part of the functions is shared with the plurality of shafts of the motors. This function allows driver505to be downsized and less expensive.

Those related art discussed above need a driving transistor or a switching section to be connected externally to one chip IC, so that a further simplification, downsizing, or cost reduction of the circuit needs integration of all the elements of the circuit that drives the motor into one chip IC. However, a temperature rise due to the loss in the one chip IC should be attentively dealt with. It has been thus difficult to integrate all the elements into one chip IC.

Meanwhile, a CD auto-changer for instance employs motors as driving sources for mounting/removing a disc, lifting/lowering a disc tray, and rotating a disc; however, those motors do not need to work together. Some of the apparatuses having a plurality of motors work in a similar way to the CD auto-changer, i.e. those motors also do not need to work together. Those some of the apparatuses are disclosed in PCT international publication number WO2002/086883. Here is another instance; a household dishwasher is equipped with a plurality of motors including a washing motor, discharging pump motor, and fan motor, and these motors work alternately. This instance is disclosed in, e.g. Unexamined Japanese Patent Publication No. 2001-286175.

A technique is thus proposed for switching over a motor to be driven in an apparatus that employs a plurality of motors and makes those motors work alternately. The proposed technique makes a plurality of motors to be driven by a driving circuit change over to each other and work alternately in the apparatus equipped with the motors that do not need to work together. The technique thus allows the motor driving circuit and its control circuit to be shared with the plurality of motors, and achieves the downsizing and the cost reduction of the apparatus.

FIG. 10shows the related art disclosed in the foregoing Unexamined Japanese Patent Publication No. 2001-286175. InFIG. 10, inverter circuit703converts a dc power of rectifying circuit702connected to ac power supply701into an ac power, and an output from inverter circuit703is switched over by load switcher704for driving a plurality of motors705A,705B sequentially. This structure allows unifying inverter circuit703with control circuit706of motors705A,705B into one body, so that the unified body can be shared with motors705A,705B.

However, this related art has the following problem. Circuit operation of the motor drive device disclosed in the foregoing Unexamined Japanese Patent Publication No. 2001-286175 is described hereinafter with reference toFIGS. 10-12.FIG. 11shows a timing chart in switching over the motors being driven by the conventional motor drive device based on the related art. The vertical axis represents waveforms of a work/stop switching signal, a motor switching signal, and a surge voltage at the switching. The horizontal axis represents a time.FIG. 12shows a timing chart in switching over the motors with the conventional motor drive device, and its vertical axis represents waveforms of work/stop switching signal, a motor switching signal, an rpm of a first motor, and an rpm of a second motor. The horizontal axis represents a time as that ofFIG. 11does.

According to the foregoing Unexamined Japanese Patent Publication No. 2001-286175, the motor drive device allows the motors to share inverter circuit703driving a plurality of motors and control circuit706, and motors705A,705B are switched over to each other by load switcher704. However, a stop of inverter circuit703generates back-electromotive force due to inertia rotation of the first motor, so that surge voltage804is generated at a power switching element of inverter circuit703. Load switcher704needs to directly switch over the lines on which a large current runs, so that it is difficult to integrate load switcher704with other elements into one chip IC. Switcher704is thus obliged to externally connect to the IC via a mechanical relay. Use of the mechanical relay in order to switch over inverter circuit703invites an arc discharge due to the surge voltage, so that a contact life of the relay becomes shorter and the reliability of the relay lowers. To overcome this problem, a given delay time905should be prepared, and then load switcher704is operated, which obliges the switching time to be longer.

DISCLOSURE OF INVENTION

A motor drive device of the present invention drives a plurality of motors alternately, and the motor drive device comprises the following elements:a position detection signal processing circuit for processing position detection signals of the plurality of motors;a pre-drive circuit for generating an excitation switching signal for the motors;a plurality of power switching circuits for supplying an electric current to the motors in response to an output from the pre-drive circuit; anda motor switching circuit for instructing a switchover of driving the motors.

The position detection signal processing circuit selects a position detection signal of a motor to be driven out of the position detection signals responsive to the motors, and inputs a position detection processed signal to the pre-drive circuit so that one of the plurality of power switching circuits can be selected for driving the motor to be driven.

The foregoing structure allows the motor drive device of the present invention to shorten a switchover time substantially in alternately driving the motors, and to generate no surge voltage or no arc discharge in the power switching circuits, so that a highly reliable motor drive device with a longer service life is obtainable.

DESCRIPTION OF REFERENCE MARKS

101drive control circuit102power output circuit103motor104motor switching circuit105one chip semiconductor element106position detection signal processing circuit107position detection output switching circuit108operation mode switching circuit109pre-drive circuit110power switching circuit111position detector112work/stop switching circuit113forward/reverse rotation switching circuit114brake mode switching circuit115power switching element116anti-parallel diode117power supply118motor switching signal119excitation switching signal119afirst motor excitation switching signal;119bsecond motor excitation switching signal;120position detection signal121position detection processed signal122work/stop switching signal123forward/reverse rotation switching signal124brake mode selecting signal130pre-drive output switching signal203output signal from position detection output switching circuit204output from a power switching circuit of a first motor205output from a power switching circuit of a second motor206rpm of first motor207rpm of second motor

PREFERRED EMBODIMENTS OF THE INVENTION

Exemplary embodiments of the present invention are demonstrated hereinafter with reference to the accompanying drawings.

FIG. 1shows a circuit structure of a motor drive device in accordance with a first embodiment of the present invention.FIG. 2shows a circuit structure more specifically drawn of the motor drive device in accordance with the first embodiment of the present invention.

InFIGS. 1 and 2, the motor drive device comprises the following elements:drive control circuit101for controlling the operation of three motors (M1, M2, and M3) and processing respective position detection signals120;power output circuit102including:pre-drive circuits109coupled to drive control circuit101for generating excitation switching signals119of motor103to be driven (one of motors M1-M3); andpower switching circuits110for supplying an electric current to motor103to be driven (one of motors M1-M3) in response to an output from pre-drive circuits109;three motors103(M1-M3) to be driven by power output circuit102; anddc power supply117.

Three power switching circuits110are prepared independently for respective motors103(M1, M2, and M3), and three pre-drive circuits109are prepared independently for each one of power switching circuits110.

A motor switching section (described later) selects one motor to be driven out of three motors103(M1-M3) in response to an instruction supplied from the outside of the motor drive device to drive control circuit101, then the selected motor is driven.

The motor switching section discussed above has the following structure and works as described below:The instruction came from outside the motor drive device is supplied to motor switching circuit104of drive control circuit101, which includes the following elements:position detection signal processing circuit106for selecting, in response to an output of motor switching circuit104, and amplifying position detection signal120of motor103(one of motors M1-M3) to be driven out of position detection signals120supplied from respective position detectors111of each one of three motors103(M1-M3); andposition detection output switching circuit107for selecting, in response to the output from motor switching circuit104, pre-drive circuit109coupled to power switching circuit110of motor103(one of motors M1-M3) to be driven, and then supplying position detection processed signal121tapped off from position detection signal processing circuit106to the selected pre-drive circuit109.

The foregoing structure allows defining correspondences between position detection signal120of motor103(one of motors M1-M3) to be driven and power switching circuit110coupled to motor103to be driven, and switching of the motor to be driven is done in response to an external instruction.

In this first embodiment, drive control circuit101includes operation mode switching circuit108having work/stop switching circuit112, forward/reverse rotation switching circuit113, and brake mode switching circuit114. This drive control circuit101and power output circuit102are integrated into one chip semiconductor element105.

Next, functions and operation of the foregoing circuits are detailed. Each one of position detectors111of respective motors103(M1-M3) detects a relative position between a permanent magnet of the rotor and the stator, and outputs position detection signal120to position detection signal processing circuit106, which then selects, in response to an output from motor switching circuit104, position detection signal120of motor103(one of motors M1, M2, M3) to be driven out of the three motors103(M1-M3). The processed signal, i.e. position detection processed signal121, is supplied to position detection output switching circuit107, which also receives the output from motor switching circuit104, whereby an output signal from position detection output switching circuit107is selected and then supplied to power output circuit102of motor103(one of motors M1-M3) to be driven.

Power output circuit102includes the following elements:pre-drive circuits109for generating excitation switching signal119of motor103(one of motors M1-M3) to be driven using an output from drive control circuit101; andpower switching circuits110for supplying an electric current, in response to the output from pre-drive circuit109, to motor103to be driven.

Pre-drive circuit109generates an excitation pattern of power switching circuit110using position detection processed signal121, supplied from position detection output switching circuit107, of motor103to be driven. Power switching circuit110is formed of a three-phase full bridge circuit including six power switching elements115. In the case of using a bi-polar transistor as power switching element115, anti-parallel diode116should be externally connected for passing a return current through supposed to occur in PWM driving. In the case of using MOSFET as power switching element115, a built-in anti-parallel diode allows passing the return current through.

Operation mode switching circuit108comprises the following elements:work/stop switching circuit112for switching the motor from work state to stop state or vice versa;forward/reverse rotation switching circuit113for switching the motor from forward rotation to reverse rotation or vice versa; andbrake mode switching circuit114for selecting one of a free-run mode which turns off all the three-phase power switching circuits110by using a motor stopping signal or a short brake mode which stops the motor within a short time by applying an electromagnetic brake.

Three motors103(M1, M2, and M3) employs three-phase brush-less motors, and position detector111employing a Hall element detects a relative position between a permanent magnet of the rotor and the stator. Instead of position detector111, what is called “a sensor-less system” can be employed for detecting back electromotive force generated on the coil of motors103, thereby obtaining position detection signal120based on the zero-cross point. This method allows further lowering the cost of the entire motor drive device.

In the foregoing structure, switching operation of three motors103(M1-M3) is described with reference toFIGS. 1-3.FIG. 3shows timing charts in switching from the first motor to the second motor in accordance with the first embodiment of the present invention.

InFIG. 3, the vertical axis represents the following items from the top: work/stop switching signal122, motor switching signal118, position detection processed signal121, output signal203from position detection output switching circuit, first motor excitation switching signal119a, output204from first motor power switching circuit, second motor excitation switching signal119b, output205from second motor power switching circuit, first motor rpm206, second motor rpm207. The horizontal axis represents a time. The low level of work/stop switching signal122indicates a stop signal, and the high level indicates a work signal. Motor switching signal118shows a first motor selecting signal at its high level, and the second motor selecting signal at its low level.

As an initial state, motor switching signal118is supplied in advance on a high level, i.e. the signal selects the first motor, to drive control circuit101from the outside, and signal118has an instruction showing which motor103(one of motors M1-M3) is to be driven. Work/stop switching signal122is supplied on a low level externally to circuit101, i.e. indicating a stop status, and forward/reverse rotation switching signal123as well as brake mode switching signal124is also supplied in an appropriate status selected respectively.

After the foregoing state is prepared, work/stop switching signal122is switched to the high level (work signal) at timing T1shown inFIG. 3, and when the work signal is supplied to work/stop switching circuit112, an output from motor switching circuit104selects first motor position detection signal120as an input to position detection signal processing circuit106because motor switching signal118is already supplied on a high level to motor switching circuit104. Then signal120is amplified by circuit106and supplied as position detection processed signal121to position detection output switching circuit107. Signal121then selects, in response to an output from motor switching circuit104, pre-drive circuit109corresponding to the first motor, and the position detection output switching circuit107outputs signal203. Then excitation switching signal119a, which is an output from pre-drive circuit109corresponding to the first motor, is supplied to power switching circuit110of the first motor, and this power switching circuit110supplies an electric current (output204from first motor power switching circuit) to the first motor, which thus starts rotating at the timing T1.

After the first motor reaches a target rpm, motor switching signal118is switched to the low level (the second motor is selected) and this low level signal is supplied to motor switching circuit104, then position detection signal120of the second motor is selected as an input to position detection signal processing circuit106, where signal120undergoes amplification, and is output as position detection processed signal121. At the timing T2onward, position detection processed signal121thus corresponds to position detection signal120of the second motor.

Position detection processed signal121is supplied to position detection output switching circuit107, and selects pre-drive circuit109, in response to an output from motor switching circuit104, corresponding to the second motor, so that position detection output switching circuit107outputs signal203. In other words, at timing T2onward, output signal203from position detection output switching circuit107corresponds to position detection signal120of the second motor. Excitation switching signal119bsupplied from pre-drive circuit109corresponding to the second motor is input to power switching circuit110of the second motor. Circuit110supplies an electric current (output205from the power switching circuit of the second motor) to the second motor, which starts rotating at the timing T2.

Simultaneously with this timing T2, the output from position detection output switching circuit107is separated from pre-drive circuit109corresponding to the first motor. Excitation switching signal119a, i.e. an output from this pre-drive circuit109becomes in a high-impedance status, so that output204from power switching circuit110of the first motor becomes also in a high-impedance status (both of the upper and lower switching elements are turned off, so that an output impedance becomes extremely high). The first motor thus stops rotating.

As discussed above, in the motor drive device which alternately drives a plurality of motors, a motor switching circuit that switches from a motor to another motor supposed to be driven employs no mechanical relay, so that contact-less switching is achievable. At the moment when the motor to be driven is switched to another one, all the three-phase power switching elements of the motor hitherto driven are turned off.

During the operation of the motor, if forward/reverse rotation switching signal123is input to drive control circuit101, or if motor switching signal118for switching from the motor approaching a target rpm to another motor supposed to be driven is input to circuit101, power switching circuit110in driving is isolated from position detection output switching circuit107as discussed above, so that the electric current cannot be supplied to the motor. Although conventional related art detects a motor stop signal, and then it should wait until a given delay time runs past before motor switching circuit104starts working. According to the present invention, however, power switching circuit110is thus kept connecting to the motor coil, which can absorb stored energy in the motor coil, so that no surge voltage or no arc discharge can be generated in power switching circuit110.

Switchover of driving the motor regardless of the switch timing is thus achievable, so that a switching time can be greatly shortened, which allows obtaining a highly reliable motor drive device having a longer service life. Since the three motors103(M1-M3) alternately rotate, power output circuit102is switched to another one coupled to the motor selected, so that only one of three power switching circuits110can be operated, and thus no increase is expected in heat generation due to consumption of electric power energy. The integration into one chip can be thus achieved with more ease.

On top of that, drive control circuit101can be shared with the three motors103, so that the circuit size is greatly downsized comparing with a case where two circuits are packed into one package. The circuit can be thus simplified and the package can be downsized, so that a more inexpensive motor drive device is obtainable.

FIG. 4shows a circuit structure of a motor drive device in accordance with the second embodiment of the present invention.FIG. 5shows the circuit structure more specifically drawn of the motor drive device in accordance with the second embodiment of the present invention. Similar elements to those in the first embodiment have the same reference marks, and the descriptions thereof are omitted here.

The second embodiment differs from the first one in an integration of pre-drive circuits109into one circuit to be shared with three motors, namely, position detection processed signal121supplied from position detection signal processing circuit106is directly input to pre-drive circuit109, of which output is supplied to pre-drive output switching circuit130, which selects, in response to an output from motor switching circuit104, power switching circuit110of motor103(one of motors M1-M3) to be driven, so that a switchover of the motor can be done. Position detection signal processing circuit106selects, in response to outputs from motor switching circuit104, position detection signal120of motor103(one of motor M1-M3) to be driven out of respective position detection signals120supplied from each one of motor103, and amplifies the selected signal120. This process of circuit106is the same as that described in the first embodiment.

The foregoing structure allows defining correspondences between position detection signal120of motor103(one of motors M1-M3) to be driven and power switching circuit110coupled to motor103to be driven, and switching of the motor to be driven is done in response to an external instruction.

In the structure discussed above, a switchover operation among three motors103(M1-M3) is demonstrated with reference toFIG. 4-FIG.6.FIG. 6shows a timing chart of switching from the first motor to the second motor out of three motors103(M1-M3) in accordance with this second embodiment.

FIG. 6differs fromFIG. 3used for the first embodiment in the following point: Excitation switching signal119supplied from pre-drive circuit109is output as the excitation switching signal of the first motor during the period from timing T5to timing T6, and excitation switching signal119is output as the excitation switching signal of the second motor after timing T6; at timing T5, switching signal118is supplied to motor switching circuit104on a high level (in a status of the first motor selecting signal), and at timing T6, motor switching signal118is supplied to circuit104on a low level (in a status of the second motor selecting signal).

The following preparations are done for the initial status: motor switching signal118having an instruction that which motor103(one of motors M1-M3) should be driven is supplied in advance on the high level (in the status of the first motor selecting signal) from the outside to drive control circuit101, and work/stop switching signal122is supplied on the low level (in halting status) to drive control circuit101, and forward/reverse switching signal123as well as brake mode switching signal124is appropriately selected its status before signal123and signal124are input to control circuit101.

After the foregoing initial status is prepared, a work signal of work/stop switching signal122is supplied to work/stop switching circuit112at timing T5shown inFIG. 6, then since motor switching signal118is already supplied to motor switching circuit104on the high level (in a status of the first motor selecting signal), position detection signal120of the first motor is selected, in response to an output from motor switching circuit104, as an input to position detection signal processing circuit106, and amplified by position detection signal processing circuit106, and then supplied as position detection processed signal121to pre-drive circuit109, which outputs excitation switching signal119to pre-drive output switching circuit130for selecting, in response to an output from motor switching circuit104, power switching circuit110corresponding to the first motor, and then signal119is output from pre-drive output switching circuit130. Other power switching circuits110corresponding to other motors than the selected first motor have the outputs from pre-drive switching circuit130in high impedance state. Power switching circuit110supplies an electric current (output204from the power switching circuit of the first motor) to the first motor, and the first motor starts rotating at the foregoing timing T5.

Next, after the motor reaches the target rpm, motor switching signal118is switched to the low level (in the status of selecting the second motor) and supplied to motor switching circuit104, then position detection signal120of the second motor is selected as an input to position detection signal processing circuit106, and amplified by position detection signal processing circuit106before signal120is supplied to pre-drive circuit109as position detection processed signal121. Pre-drive circuit109outputs excitation switching signal119to pre-drive output switching circuit130for selecting, in response to an output from motor switching circuit104, power switching circuit110corresponding to the second motor, and then signal119is supplied from pre-drive output switching circuit130. In other words, excitation switching signal119is generated from position detection signal120of the second motor by pre-drive circuit109, and then supplied from pre-drive output switching circuit130to power switching circuit110corresponding to the second motor. Power switching circuit110supplies an electric current (output205from the power switching circuit of the second motor) to the second motor, and the second motor starts rotating at the foregoing timing T6.

At the foregoing timing T6, pre-drive output switching circuit130supplies an output in the high impedance state to power switching circuit110corresponding to the first motor, and output204from power switching circuit110becomes also in the high impedance state, so that the first motor stops rotating.

The second embodiment thus produces a similar advantage to that of the first embodiment.

INDUSTRIAL APPLICABILITY

A motor drive device of the present invention is useful for a variety of audio & video apparatuses, office automation apparatuses, and home appliances, each of which apparatuses employs a plurality of motors working alternately.