Sewing machine

A feed dog drive motor and an X-direction motor are connected to common input/output ports of a CPU via first and second driver IC circuits, respectively. In response to a drive switching signal generated from the CPU, selected one of the first and second driver IC circuits is enabled, causing the feed dog drive motor and the X-directional motor to selectively energize. A common driver IC circuit can be used in place of the first and second driver IC circuits. With such a configuration, the number of input/output ports of the CPU as well as the number of driver IC circuits can be reduced.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priorities to Japanese Patent Application Nos. 2005-115488 filed on Apr. 13, 2005, the contents of which are hereby incorporated by reference into the present application.

TECHNICAL FIELD

The present invention relates to a sewing machine comprising first and second driving mechanisms for driving a workpiece during a sewing operation, and first and second electric actuators for driving the first and second driving mechanisms with different drive currents. The present invention particularly relates to a sewing machine with a reduced number of driver circuits for driving the electric actuators and a reduced number of input/output ports in a CPU of the sewing machine.

BACKGROUND

Various sewing machines capable of sewing desired embroidery patterns on a workpiece set in an embroidery frame by mounting an embroidery device in an electronic sewing machine capable of sewing utility patterns such as zigzag stitches and triple stitches, and common patterns including various ornamental patterns have been commercialized and proposed. Recent electronic sewing machines are being provided with a workpiece feeding distance modifying motor for modifying the tilt of a feeding regulator in a feed dog driving mechanism fox driving the feed dog to move a workpiece; a needle swing motor for driving a needle swinging mechanism to pivot a needle bar; a frame moving motor built into the embroidery device for driving the embroidery frame in two directions orthogonal to one another (X- and Y-directions); and the like.

For example, a sewing machine described in Japanese unexamined patent application publication No. HEI-11-164976 includes a needle bar driving mechanism for driving the needle bar vertically; a needle bar swinging mechanism for swinging the needle bar; a thread take-up driving mechanism for driving the thread take-up; a forward/rearward feed dog driving mechanism for driving the feed dog forward and rearward; and the like. The sewing machine also includes a stepping motor for driving the needle bar swinging mechanism; a stepping motor for driving the forward/rearward feed dog moving mechanism; a stepping motor for driving a left/right driving mechanism provided in the embroidery device; and a stepping motor for driving a forward/rearward driving mechanism.

In order to drive the stepping motors with this construction, a driver circuit for each stepping motor is necessary for supplying a drive current to an excitation coil. Further, a plurality of input/output ports and the like are required in a control device for supplying an excitation signal comprising a step pulse to each driver circuit.

A sewing machine capable of sewing embroidery patterns according to Japanese unexamined patent application publication No. HEI-11-164976 described above is provided with stepping motors for swinging the needle bar and for driving the feed dog, and the embroidery device is provided with stepping motors for moving the embroidery frame left and right and forward and rearward. Hence, not only are a plurality of driver circuits required for driving each of the stepping motors, but the CPU in the controller requires 4-8 input/output ports for these stepping motors according to the number of excitation phases.

Recent computerized sewing machines equipped with numerous functions include not only the stepping motors described above, but also numerous stepping motors for an automatic thread guard mechanism, automatic thread adjusting mechanism, electronic thread cutting mechanism, automatic threading mechanism, thread winding mechanism, and the like. As the number of stepping motors increases, not only does the number of driver circuits increase, but also does the number of input/output ports required in the CPU for connecting the CPU to these driver circuits.

A CPU having a large number of input/output ports is generally more expensive than a CPU with few ports, leading to an increase in the cost of the sewing machine. Further, since a CPU with a large number of input/output ports is generally larger in size, the circuit board on which this large CPU is mounted is also larger in size, leading to an increased size of the sewing machine.

Further, since the operating properties of these driving mechanisms differ according to each use, the magnitude of the torque for driving the driving mechanisms also differs. As a result, since the drive currents supplied to the stepping motors for driving the driving mechanisms differ, a universal driver circuit cannot be used to drive all the stepping motors.

While it is conceivable to connect an ASIC (Application Specific Integrated Circuit), and particularly gate array IC chips, to the input/output ports of the CPU to reduce the number of required I/O ports, these gate array IC chips are configured of LSI chips manufactured individually according to specification and are therefore more expensive.

SUMMARY

In view of the foregoing, to use a CPU with a reduced number of input/output ports, a sewing machine according to one aspect of the invention includes first and second driving mechanisms, first and second electric actuators, a CPU, first and second driver circuits, a switching unit, and a voltage regulating circuit. The first driving mechanism moves a workpiece during a first sewing operation. The second driving mechanism moves a workpiece during a second sewing operation. Either the first or the second driving mechanism is selectively driven. The first electric actuator drives the first drive mechanism with a first drive current, and the second electric actuator drives the second drive mechanism with a second drive current different from the first drive current. The CPU controls the first and second electric actuators and has input/output ports including common input/output ports. The first driver circuit is connected between the common input/output ports of the CPU and the first electric actuator, and the second driver circuit is connected between the common input/output ports of the CPU and the second electric actuator. The switching unit performs a switching action to selectively activate either one of the first and second electric actuators. The voltage regulating circuit is connected between one of the input/output ports of the CPU and the first driver circuit and between the one of the input/output ports of the CPU and the second driver circuit for applying a voltage corresponding to the first drive current to the first driver circuit and applying a voltage corresponding to the second drive current to the second driver circuit in synchronization with the switching action of the operation switching unit.

With the above-described configuration, even though the first and second electric actuators are connected to the common input/output ports of the CPU, the switching unit selectively switches operations of the first and second electric actuators. Moreover, the voltage regulating unit applies a voltage corresponding to the first or second drive current to the corresponding driver circuit in synchronization with the switching unit.

Accordingly, even when the drive currents of the first and second electric actuators are different due to a different magnitude of torque required for driving the first and second driving mechanisms or when the first and second electric actuators are connected to the common input/output ports of the CPU, the sewing machine can drive the first electric actuator with an appropriate drive current for this actuator and can drive the second electric actuator with a drive current appropriate for that actuator.

According to another aspect of the invention, to further attain reduction of the number of driving circuits, there is provided a sewing machine that includes first and second drive mechanisms, first and second electric actuators, a CPU, a common driver circuit, a switching unit, and a control pulse signal generator. The first driving mechanism moves a workpiece during a first sewing operation, and the second driving mechanism moves a workpiece during a second sewing operation. Either the first or the second driving mechanism is selectively driven. The first electric actuator drives the first drive mechanism with a first drive current, and the second electric actuator drives the second drive mechanism with a second drive current different from the first drive current. The CPU controls the first and second electric actuators and has input/output ports including common input/output ports. The common driver circuit is connected between the common input/output ports of the CPU and the first and second electric actuators. The switching unit performs a switching action to selectively activate either one of the first and second electric actuators. The control pulse signal generator adjusts a duty ratio of a control signal supplied to the common driver circuit so that the common driver circuit outputs a drive current for the respective first and second electric actuators in response to the switching unit.

With the above-described configuration, the switching unit can selectively switch activation between the first or second electric actuators, even when the first and second electric actuators are connected to the common input/output ports of the CPU via the common driver circuit. Moreover, the control pulse signal generator supplies a control pulse with an adjusted duty ratio to the driver circuit in response to the switching unit that switches activation between the first and second electric actuators in order that the driver circuit supplies a drive current appropriate to the respective first or second electric actuator.

Accordingly, even when the drive currents of the first and second electric actuators are different due to a different magnitude of torque required for driving the first and second driving mechanisms or when the first and second electric actuators are connected to the common input/output ports of the CPU via the common driver circuit, the sewing machine can drive the first electric actuator with an appropriate drive current for this actuator an can drive the second electric actuator with a drive current appropriate for that actuator.

DETAILED DESCRIPTION

A sewing machine according to an embodiment of the present invention is equipped with a feed dog drive motor and an X-direction motor for driving a forward/rearward feed dog moving mechanism and an X-direction driving mechanism of an embroidery frame moving mechanism, which are not operated simultaneously. In this case, the feed dog drive motor and X-direction motor are connected to common input/output ports of the CPU and are driven by individual driver circuits.

FIG. 1shows a computerized sewing machine M according to the preferred embodiment. An embroidery frame moving mechanism20described later is mounted on the sewing machine M for sewing embroidery patterns. As shown inFIG. 1, the sewing machine M includes a sewing bed1, an arm support2erected from the right end of the sewing bed1, and an arm3that extends leftward inFIG. 1from the top end of the arm support2so as to confront the sewing bed1.

The sewing bed1is provided with a vertical feed dog moving mechanism (not shown) for moving a feed dog up and down; a forward/rearward feed dog moving mechanism (not shown) for moving the feed dog forward and rearward; a thread loop catcher, such as a horizontal bobbin, accommodating a bobbin and working in cooperation with a stitching needle6; and the like.

The arm3includes a needle bar driving mechanism (not shown) for moving a needle bar5vertically, the needle bar5having the stitching needle6mounted in the bottom end thereof; a needle bar pivoting mechanism (not shown) for pivoting the needle bar5in a direction orthogonal to the direction in which a workpiece is fed; a thread take-up driving mechanism (not shown) for driving a thread take-up (not shown) vertically in sync with the vertical movement of the needle bar5; and the like.

As shown inFIG. 2, a sewing motor15drives the vertical feed dog moving mechanism, the needle bar driving mechanism, and the thread take-up driving mechanism. A needle swing motor16drives the needle bar pivoting mechanism. A feed dog drive motor17drives the forward/rearward feed dog moving mechanism. The needle swing motor16and the feed dog drive motor17are each configured of a stepping motor.

As shown inFIG. 1, the arm3includes a head portion4on the end farthest from the arm support2. A sewing switch7for manually starting and stopping sewing operations is provided on the head portion4. A color liquid crystal display (hereinafter simply referred to as “display”)8is provided on the front surface of the arm3. The display8functions to display various stitching patterns, including utility patterns and embroidery patterns, pattern names, various function names, various messages, and the like.

Touch keys (not shown) formed of transparent electrodes are disposed substantially on the front surface of the display8. By pressing desired touch keys, the user can select a desired pattern to be sewed or indicate a function. A detailed description of these patterns and functions is not included herein.

A free head portion, commonly called a free arm, is formed on the left end of the sewing bed1inFIG. 1. The embroidery frame moving mechanism20(also referred to as an embroidery device) is detachably mounted on this free head portion.

The embroidery frame moving mechanism20includes a main case20a, an embroidery frame21in which a cloth workpiece is detachably mounted, a Y-direction drive unit22having a built-in Y-direction driving mechanism for moving the embroidery frame21in a Y-direction (front-to-rear direction), and an X-direction driving mechanism (not shown) accommodated in the main case20afor driving the Y-direction drive unit22in the X-direction (left-to-right direction). The embroidery frame moving mechanism20also includes an X-direction motor23(seeFIG. 2) for driving the X-direction driving mechanism, and a Y-direction motor24(seeFIG. 2) for driving the Y-direction driving mechanism. In the preferred embodiment, the X-direction motor23and Y-direction motor24axe configured of stepping motors.

When the embroidery frame moving mechanism20is mounted on the free head portion, the X-direction motor23and Y-direction motor24are electrically connected to a controller25(seeFIG. 2) fox the sewing machine M via a connector10. The controller25controls the driving of the X-direction motor23and Y-direction motor24so that the embroidery frame21in which the workpiece is set can be moved independently in the X- and Y-directions, while sewing an embroidery pattern.

Next, a control system of the sewing machine M will be described with reference toFIG. 2. As shown inFIG. 2, the controller25includes a circuit board25A on which are provided a computer that includes a CPU26having a plurality of input/output ports (I/O port group26A), a ROM27, a RAM28, and a nonvolatile flash memory29that can be electrically rewritten; a plurality of driver circuits30-35; and the like. The sewing switch7described above, a timing signal generator9for detecting the rotational phase of a main sewing shaft, and the like are connected to the I/O port group26A.

The driver circuits30-35are also connected to the I/O port group26A. These driver circuits30-35are also individually connected to the motors15-17described above, the display8, and the X-direction and Y-direction motors23and24of the embroidery frame moving mechanism20via the connector10.

In addition to common control programs for controlling the sewing of common stitches including utility patterns, and for controlling the display, the ROM27stores an editing program for editing a selected embroidery pattern displayed on the display8through such processes as enlargement, reduction, and rotation; a sewing control program for sewing a selected embroidery pattern; and the like.

The RAM28is provided with various memory areas required for performing the various control processes described above, such as memory areas for flags, pointers, counters, and the like, as well as registers and buffers.

Next, a description will be given of the driver circuit32and driver circuit34connected to the I/O port group26A of the CPU26, and the feed dog drive motor17(hereinafter called the “F motor”) and the X-direction motor23(hereinafter called the “X motor”) connected to the driver circuit32and driver circuit34respectively, and a voltage regulating circuit40. The voltage regulating circuit40applies a voltage to the driver circuit32and driver circuit34corresponding to the excitation drive current suited to the motors17and23, respectively. The voltage is applied at the same time activation of the F motor17and X motor23is switched.

As shown inFIG. 3, the I/O port group26A of the CPU26includes four common excitation phase output ports26afor outputting excitation phase signals used for two-phase or four-phase excitation of excitation coils in the F motor17and X motor23; an output current switching port26bfor outputting a three-state signal, causing the voltage regulating circuit40to output a voltage corresponding to the excitation drive current applied to the F motor17and X motor23; and a driver switching port26cfor outputting a driver switching signal to selectively switch activation of the driver circuit32and driver circuit34.

The driver circuit32includes four excitation signal input terminals32afor receiving excitation signals from the CPU26; four excitation current output terminals32bconnected to an excitation coil (not shown) in the F motor17; an output current switching terminal32cfor receiving an output current switching voltage from the voltage regulating circuit40; and a switching terminal32dfor receiving an inputted driver switching signal.

The driver circuit34includes four excitation signal input terminals34afor receiving inputted excitation signals from the CPU26; four excitation current output terminals34bfor outputting an excitation drive current to an excitation coil (not shown) in the X motor23; an output current switching terminal34cfor receiving an output current switching voltage from the voltage regulating circuit40; and a switching terminal34dfor receiving an inputted driver switching signal.

The voltage regulating circuit40includes a first input terminal40aconnected to the output current switching port26bfor receiving a three-state signal therefrom; a second input terminal40bconnected to the driver switching port26cand the switching terminal34d; and an output terminal40cfor outputting an output current switching voltage to the output current switching terminals32cand34c.

As shown inFIG. 3, the four excitation phase output ports26aprovided in the I/O port group26A are connected both to the four excitation signal input terminals32aprovided on the driver circuit32, and the four excitation signal input terminals34aprovided on the driver circuit34. In other words, the driver circuit32and driver circuit34share connections to the excitation phase output ports26aof the CPU26.

When the excitation signal input terminals32areceive an excitation phase signal from the CPU26, the driver circuit32outputs an excitation drive current via the excitation current output terminals32bto the F motor17. The outputted excitation drive current corresponds to an output current switching voltage that the voltage regulating circuit40has applied to an output current switching terminal32cof the driver circuit32. However, the driver circuit32operates only when a HIGH level driver switching signal is supplied to the switching terminal32d.

Similarly, when the excitation signal input terminals34aof the driver circuit34receives an excitation phase signal from the CPU26, the excitation current output terminals34boutput an excitation drive current to the X motor23corresponding to an output current switching voltage that the voltage regulating circuit40has applied to the output current switching terminal34c. However, the driver circuit34only operates when a HIGH level driver switching signal is supplied to the switching terminal34d.

When the driver switching port26cof the CPU26outputs a HIGH level driver switching signal, this signal is supplied directly to the switching terminal34dof the driver circuit34so that the driver circuit34is activated. However, the HIGH level driver switching signal passes through an inverter41before being supplied to the switching terminal32d. The inverter41inverts the HIGH level signal to a LOW level signal. Accordingly, the driver circuit32is not activated.

Here, an operation switching mechanism is configured of the driver switching port26c, the inverter41, and the like. However, when the driver switching port26cof the CPU26outputs a LOW level driver switching signal, the driver circuit32operates, but the driver circuit34does not operate. In this way, the driver switching signal is used to selectively switch which of the driver circuit32and driver circuit34operates.

Next, the voltage regulating circuit40will be described in greater detail. As shown inFIG. 4, the voltage regulating circuit40is configured of a voltage divider circuit having a plurality of resistors R1-R7, and an NPN transistor43. The first input terminal40aand output terminal40care connected by a main wire44. The resistor R1is connected in series on the main wire44. Two resistors R2and R3are connected on one end to the main wire44and grounded on the other end. A +5 V terminal is connected to the main wire44via a pull-up resistor R4.

The second input terminal40bis connected to the base of the NPN transistor43via the resistor R6, while the collector of the NPN transistor43is connected to the main wire44via the resistor R5and the emitter of the NPN transistor43is connected to the main wire44via a wire45A bias resistor R7is also connected to the base of the NPN transistor43. Therefore, the first input terminal40ais connected to the output current switching port26bof the CPU26; the output terminal40cis connected to the output current switching terminal32cand output current switching terminal34cof the driver circuit32and driver circuit34, respectively; and the second input terminal40bis connected to the driver switching port26cof the CPU26.

The output current switching port26bof the CPU26selectively outputs three signals (referred to as a “three-state signal”) to the first input terminal40a. The three-state signal is configured of a LOW level signal, a HIGH level signal, and a high impedance signal. In addition, the driver switching port26coutputs a LOW level driver switching signal for operating the driver circuit32and a HIGH level driver switching signal for operating the driver circuit34.

As described above, the output current switching port26boutputs the LOW level signal when the F motor17and X motor23are at rest and not being driven, preventing inadvertent rotation of the F motor17and X motor23. The output current switching port26boutputs the HIGH level signal when exciting and driving the F motor17and X motor23.

The output current switching port26boutputs a high impedance signal when performing a process to initialize the F motor17and X motor23when the power of the sewing machine M is turned on. In this initialization process, the F motor17and X motor23are driven until a positioning piece contacts the frame of the sewing machine M. However, since the F motor17and X motor23are made to step out during initialization, the motors are driven by a lower excitation current than a normal driving current to ensure a quiet initialization process.

Hence, when the driver switching port26coutputs a LOW level driver switching signal to the second input terminal40bof the voltage regulating circuit40, the NPN transistor43does not operate. An equivalent circuit of the voltage regulating circuit40shown inFIG. 5Ais configured of a first voltage divider circuit having four resistors R1-R4.

In this equivalent circuit, the output terminal40cof the voltage regulating circuit40outputs voltages of 1.72 V, 3.42 V, and 2.91 V to the output current switching terminals32cand34cof the driver circuits32and34, respectively, when the output current switching port26boutputs a LOW level signal (0 V), HIGH level signal (3 V), and high impedance signal, respectively, as shown inFIG. 6. Since the driver circuit32has been enabled based on the LOW level driver switching signal from the driver switching port26c, the excitation current output terminals32boutputs excitation drive currents of 0.40 A, 0.80 A, and 0.65 A to the F motor17in response to the above output voltages.

However, when the driver switching port26coutputs the HIGH level driver switching signal to the second input terminal40bof the voltage regulating circuit40, the NPN transistor43is activated. An equivalent circuit of the voltage regulating circuit40shown inFIG. 5Bis configured of a second voltage divider circuit having five resistors R1-R5.

In this equivalent circuit, the output terminal40cof the voltage regulating circuit40outputs voltages of 0.88 V, 3.10 V, and 2.40 V to the output current switching terminals32cand34cof the driver circuits32and34, respectively, when the output current switching port26boutputs a LOW level signal (0 V), HIGH level signal (3 V), and high impedance signal, respectively, to the first input terminal40a, as shown inFIG. 7. Since driver circuit34has been activated based on the HIGH level driver switching signal from the driver switching port26c, the excitation current output terminals34boutputs excitation drive currents of 0.21 A, 0.70 A, and 0.56 A to the X motor23in response to the above output voltages.

Hence, three voltages corresponding to three types of drive currents suitable for the F motor17and X motor23are applied to the driver circuits32and34in synchronization with the driver switching port26coutputting a driver selection signal for switching which of the F motor17and X motor23is activated.

The resistors R1-R7of the voltage regulating circuit40have been selected to output the voltages shown inFIGS. 6 and 7based on the output current switching signals (three-state signal). However, these resistors are suitably adjusted according to the driving characteristics (drive currents) of the motors.

Next, the operations of the sewing machine M having the above construction will be described. In this description, the F motor17is driven for moving the feed dog forward and rearward to execute normal stitching, while the X motor23is driven for moving the embroidery frame when the embroidery frame moving mechanism20is mounted on the free head portion to sew an embroidery pattern. Hence, the F motor17and X motor23are never driven simultaneously. Moreover, the excitation drive current supplied to the F motor17is larger than that supplied to the X motor23in order to generate a large feeding torque with the feed dog and a holding torque for maintaining the position of the feed dog.

First, the case of performing common stitches when the embroidery frame moving mechanism20is not mounted will be described. In this case, when the power switch is turned on, the CPU26is initialized according to a reset signal, while a LOW level driver switching signal is outputted from the driver switching port26c. Accordingly, a LOW level signal is supplied to the second input terminal40bof the voltage regulating circuit40, while the inverter41inverts the LOW level signal to a HIGH level driver switching signal for activating the driver circuit32.

Since the voltage regulating circuit40has the equivalent circuit shown inFIG. 5Aat this time, based onFIG. 6, the output current switching port26bof the CPU26supplies a high impedance signal to the first input terminal40a, and the output terminal40coutputs a voltage of 2.91 V to the output current switching terminal32cof the driver circuit32for initializing the F motor17. Hence, the driver circuit32supplies an excitation drive current of 0.65 A to the F motor17.

When initialization is completed, the CPU26outputs a LOW level signal to the voltage regulating circuit40from the output current switching port26b. Hence, the voltage regulating circuit40outputs a voltage of 1.72 V to the driver circuit32, and the driver circuit32supplies an excitation drive current of 0.40 A to the F motor17.

However, since the CPU26outputs a HIGH level signal to the voltage regulating circuit40from the output current switching port26bfor driving the F motor17, the voltage regulating circuit40outputs a voltage of 3.42 V to the driver circuit32. Accordingly, the driver circuit32can supply an excitation drive current of 0.80 A. At this time, upon receiving an excitation phase signal from the CPU26, the driver circuit32supplies an excitation drive current of 0.80 A in pulses to the F motor17based on the excitation phase signal.

Next, an example will be described for sewing an embroidery pattern. In this case, the CPU26is initialized by the reset signal when the power switch of the sewing machine M is turned on, and the driver switching port26coutputs a HIGH level driver switching signal. Therefore, a HIGH level signal is supplied to the second input terminal40bof the voltage regulating circuit40, and the driver circuit34is activated by the HIGH level driver switching signal.

Since the voltage regulating circuit40has the equivalent circuit shown inFIG. 5Bat this time, based onFIG. 7, the output current switching port26bof the CPU26supplies a high impedance signal to the first input terminal40a, and the output terminal40coutputs a voltage of 2.40 V to the output current switching terminal34cof the driver circuit34for initializing the X motor23. Hence, the driver circuit34supplies an excitation drive current of 0.56 A to the X motor23.

When initialization is completed, the CPU26outputs a LOW level signal to the voltage regulating circuit40from the output current switching port26b. Hence, the voltage regulating circuit40outputs a voltage of 0.88 V to the driver circuit34, and the driver circuit34supplies an excitation drive current of 0.21 A to the X motor23.

However, since the CPU26outputs a HIGH level signal to the voltage regulating circuit40from the output current switching port26bfor driving the X motor23, the voltage regulating circuit40outputs a voltage of 3.10 V to the driver circuit34. Accordingly, the driver circuit34can supply an excitation drive current of 0.70 A. At this time, upon receiving an excitation phase signal from the CPU26, the driver circuit34supplies an excitation drive current of 0.70 A in pulses to the X motor23based on the excitation phase signal.

In this way, the F motor17and X motor23are connected to the excitation phase output ports26a, serving as common input/output ports of the CPU26, via the driver circuits32and34, and the voltage regulating circuit40is provided for selectively switching which of the F motor17and X motor23are operated. Accordingly, both the F motor17and the X motor23can be driven with an appropriate drive current, even when the drive currents for the F motor17and X motor23are different due to a difference in the magnitude of torque required for driving the forward/rearward feed dog moving mechanism and for driving the X-direction driving mechanism and when the F motor17and X motor23are connected to common excitation phase output ports26aof the CPU26. In addition, this construction can also minimize the number of input/output ports required in the CPU26and greatly reduce the cost of the CPU26.

Further, the driver circuits32and34are connected to the F motor17and X motor23, respectively, and are selectively activated based on a driver switching signal outputted from the driver switching port26c. Hence, the construction for switching which of the driver circuits32and34is activated can be simplified.

Next, variations of the preferred embodiment will be described.

(1) While not shown in the drawings, the sewing machine M may be provided with a horizontal feed dog moving mechanism for moving the feed dog by fine degrees in the left and right direction (the direction orthogonal to the workpiece feeding direction), and a stepping motor for driving the horizontal feed dog moving mechanism. The first driving mechanism is the Y-direction driving mechanism of the embroidery frame moving mechanism20described above, while the second driving mechanism is the horizontal feed dog moving mechanism. The first electric actuator may be the Y-direction motor24, and the second electric actuator the stepping motor for moving the feed dog horizontally.

In this variation, both the Y-direction motor24for driving the Y-direction driving mechanism of the embroidery frame moving mechanism20and the stepping motor for driving the horizontal feed dog moving mechanism can be driven with appropriate drive currents, even when the Y-direction motor24requires a larger excitation drive current than the stepping motor.

(2) While not shown in the drawings, the sewing machine M may be provided with a thread cutting mechanism for cutting thread with a fixed blade and a movable blade, and a stepping motor for driving the movable blade. Further, the sewing machine M may be provided with a thread adjusting mechanism for adjusting the sewing thread by pinching the thread between a pair of thread adjustment plates including a fixed plate and a movable plate, and a stepping motor for pressing the movable plate against the fixed plate. Here, the first driving mechanism is the thread cutting mechanism, while the second driving mechanism is the thread adjusting mechanism. Further, the first electric actuator is the stepping motor for driving the movable blade, while the second electric actuator is the stepping motor for adjusting the thread.

In this case, both the stepping motor for driving the thread cutting mechanism and the stepping motor for driving the thread adjusting mechanism can be driven at appropriate drive currents, even when the stepping motor for driving the movable blade requires a larger excitation drive current than the thread adjustment stepping motor.

(3)FIG. 8shows an example of a single third driver circuit36used to drive both the F motor17and X motor23. Specifically, the driver circuit36includes four excitation signal input terminals36aconnected to the excitation phase output ports26aof the CPU26, four excitation current output terminals36b, and an output current switching terminal36cconnected to the output terminal40cof the voltage regulating circuit40. The excitation current output terminals36bare connected to four common terminals (indicated by ⊚) provided in a relay (magnetic switch)37. The relay37has four b contact points (indicated by ◯) connected to an excitation coil in the F motor17, four a contact points (indicated by ●) connected to an excitation coil in the X motor23, and a coil37a.

The relay37includes four sets of dual-circuit switches that are switched simultaneously. Hence, when the driver switching port26cof the CPU26supplies a LOW level relay switching signal to the coil37aof the relay37, the relay37does not switch, and the four common terminals and the corresponding b contact points are short-circuited. As a result, the excitation drive current outputted from the excitation current output terminals36bis supplied to the F motor17. Here, the relay37, driver switching port26c, and the like constitute the switching mechanism.

However, when the driver switching port26csupplies a HIGH level relay switching signal to the coil37aof the relay37, the relay37switches, short-circuiting the four common terminals and the four a contact points. As a result, the excitation drive current outputted from the excitation current output terminals36bis supplied to the X motor23.

Therefore, when executing normal stitches, the CPU26outputs a LOW level relay switching signal from the driver switching port26cwhen the power switch is turned on. Accordingly, a LOW level signal is supplied to the second input terminal40bof the voltage regulating circuit40and causes the relay37to switch.

Since the voltage regulating circuit40has the equivalent circuit shown inFIG. 5Aat this time, based onFIG. 6, the output current switching port26bof the CPU26supplies a high impedance signal to the first input terminal40a, and the output terminal40coutputs a voltage of 2.91 V to the output current switching terminal36cof the driver circuit36for initializing the F motor17. Hence, the driver circuit36supplies an excitation drive current of 0.65 A to the F motor17via the relay37.

When initialization is completed, the CPU26outputs a LOW level signal to the voltage regulating circuit40from the output current switching port26b. Hence, the voltage regulating circuit40outputs a voltage of 1.72 V to the driver circuit36, and the driver circuit36supplies an excitation drive current of 0.40 A to the F motor17via the relay37.

However, since the CPU26outputs a HIGH level signal to the voltage regulating circuit40from the output current switching port26bfor driving the F motor17, the voltage regulating circuit40outputs a voltage of 3.42 V to the driver circuit36. Accordingly, the driver circuit36can supply an excitation drive current of 0.80 A. At this time, upon receiving an excitation phase signal from the CPU26, the driver circuit36supplies an excitation drive current of 0.80 A in pulses to the F motor17via the relay37based on the excitation phase signal.

When sewing an embroidery pattern, the driver switching port26cof the CPU26outputs a HIGH level driver switching signal when the power switch of the sewing machine M is turned on. Therefore, a HIGH level signal is supplied to the second input terminal40bof the voltage regulating circuit40, and the relay37is switched by the HIGH level driver switching signal.

Since the voltage regulating circuit40has the equivalent circuit shown inFIG. 5Bat this time, based onFIG. 7, the output current switching port26bof the CPU26supplies a high impedance signal to the first input terminal40a, and the output terminal40coutputs a voltage of 2.40 V to the output current switching terminal36cof the driver circuit36for initializing the X motor23. Hence, the driver circuit36supplies an excitation drive current of 0.56 A to the X motor23via the relay37.

When initialization is completed, the CPU26outputs a LOW level signal to the voltage regulating circuit40from the output current switching port26b. Hence, the voltage regulating circuit40outputs a voltage of 0.88 V to the driver circuit36, and the driver circuit36supplies an excitation drive current of 0.21 A to the X motor23via the relay37.

However, since the CPU26outputs a HIGH level signal to the voltage regulating circuit40from the output current switching port26bfor driving the X motor23, the voltage regulating circuit40outputs a voltage of 3.10 V to the driver circuit36. Accordingly, the driver circuit36can supply an excitation drive current of 0.70 A. At this time, upon receiving an excitation phase signal from the CPU26, the driver circuit36supplies an excitation drive current of 0.70 A to the X motor23via the relay37based on the excitation phase signal.

In this example, a single driver circuit36is connected to the F motor17and X motor23, and the relay37is provided to selectively supply the drive current outputted from the driver circuit36to either the F motor17or the X motor23. Hence, by providing a simple relay37, it is possible to decrease the number of costly driver circuits and to reduce the cost required for manufacturing the forward/rearward feed dog moving mechanism and the embroidery frame moving mechanism20.

(4) The sewing machine M may also be provided with a thread cutting mechanism for cutting a sewing thread and bobbin thread with a fixed blade and a movable blade, and a solenoid for driving the movable blade. Further, the sewing machine M may be provided with a thread adjusting mechanism for adjusting the sewing thread by pinching the thread between a pair of thread adjustment plates including a fixed plate and a movable plate, and a solenoid for pressing the movable plate against the fixed plate.FIG. 9shows a construction for driving both the thread adjustment solenoid and movable blade driving solenoid with a single driver circuit.

Specifically, a driver circuit52and a relay53are connected in series to a pulse control port26dprovided in the I/O port group26A of the CPU26. The driver circuit52is configured of a NPN transistor52a. The relay53includes one set of dual-circuit switches, and a coil53a. Hence, the pulse control port26dis connected to a base of the NPN transistor52avia a resistor R10, while the collector of the NPN transistor52ais connected to a common terminal (indicated by ⊚) of the relay53. A b contact point (indicated by ◯) of the relay53is connected to a terminal of a thread adjustment solenoid50. A DC voltage (+V) is applied to the other end of the thread adjustment solenoid50.

An a contact point (indicated by ●) of the relay53is connected to a terminal of a movable blade solenoid51. A DC voltage (+V) is applied to the other end of the movable blade solenoid51. When the thread adjustment mechanism adjusts the thread during a sewing operation, the driver switching port26cof the CPU26supplies a LOW level solenoid switching signal to the coil53aof the relay53. In this case, the relay53is not switched. Hence, the common terminal is connected to the b contact point, and the thread adjustment solenoid50is activated.

However, when the sewing process is completed and the thread cutting mechanism performs a cutting operation, the driver switching port26cof the CPU26supplies a HIGH level solenoid switching signal to the coil53a. In this case, the relay53is switched so that the common terminal is connected to the a contact point. As a result, the movable blade solenoid51is activated in this example, the relay53, driver switching port26c, and the like constitute the operation switching mechanism.

The CPU26has various registers for setting a timer output, a counter, a clear counter cause, a period, and a duty value. When a start count command is received, the pulse control port26doutputs a control pulse having the duty ratio set in the duty value register.

For example, when a LOW level solenoid switching signal is outputted at the beginning of a sewing operation, the duty ratio is set to 25%, as shown inFIG. 11. Consequently, a pulse width modulated (PWM) control pulse with a duty ratio of 25% is outputted, as shown inFIG. 10A.

As shown inFIG. 11, when a HIGH level solenoid switching signal is outputted for cutting thread after a sewing process, the duty ratio is set to 50%. Consequently, a PWM control pulse having a duty ratio of 50% is outputted as shown inFIG. 10B.

As described above, the duty ratio is set to 25% in the CPU26when adjusting the thread during a sewing operation. Accordingly, the pulse control port26doutputs a control pulse having a duty ratio of 25% to the NPN transistor52aof the driver circuit52. At the same time, the driver switching port26csupplies a LOW level solenoid switching signal to the coil53aso that the relay53does not switch.

At this time, the NPN transistor52aconducts electricity when the control pulse applied to the base is High level, and the thread adjustment solenoid50operates by a direct current supplied from a DC power supply. As shown inFIG. 9, the thread adjustment solenoid50operates by a drive pulse having a prescribed period of 25%, identical to the control pulse having the duty ratio of 25%. Therefore, when the thread adjustment solenoid50is activated, the duty ratio is adjusted to 25% in response.

However, when the sewing process is completed and the thread cutting mechanism performs a thread cutting operation, the duty ratio in the CPU26is set to 50%, as described above. Hence, the pulse control port26doutputs a control pulse with a duty ratio of 50% to the NPN transistor52a. At the same time, the driver switching port26csupplies a HIGH level solenoid switching signal to the coil53aso that the relay53is switched.

At this time, the NPN transistor52aconducts electricity when the control pulse applied to the base is at HIGH level, at which time the movable blade solenoid51is activated. In this case, as shown in.FIG. 9, the movable blade solenoid51operates at a prescribed period of 50%, just like the control pulse having the duty ratio of 50%. Therefore, when the movable blade solenoid5.1is activated, the duty ratio is adjusted to 50% in response.

With this construction, the thread adjustment solenoid50and movable blade solenoid51are connected to the pulse control port26d, serving as a common input/output port of the CPU26via the common driver circuit52, and the relay53is used to selectively switch whether the thread adjustment solenoid50or movable blade solenoid51is activated. In response to the relay53switching activation of the thread adjustment solenoid50and movable blade solenoid51, the duty ratio of the control pulse supplied to the driver circuit52is adjusted so that the driver circuit52outputs a suitable drive current to the thread adjustment solenoid50or movable blade solenoid51. Accordingly, both the thread adjustment solenoid50and movable blade solenoid51can be driven by suitable drive currents, even when the drive pulse for the thread adjustment solenoid50and movable blade solenoid51differ due to differing magnitudes of torque required to drive the thread adjusting mechanism and the thread cutting mechanism and even when the thread adjustment solenoid50and movable blade solenoid51are connected to a common pulse control port26dof the CPU26via a common driver circuit52. In addition, this construction can minimize the number of input/output ports required in the CPU26and the number of driver circuits52, thereby minimizing the cost required for constructing the CPU26, the thread adjusting mechanism, and the thread cutting mechanism.

(5) As described above; the pulse control port26dis configured to output control pulses having different duty ratios by modifying the settings for registers in the CPU26. However, it is possible to provide a control pulse signal generating circuit between the CPU26and the driver circuit52that can output various control pulses (PWM signals) having different duty ratios.

(6) When the first and second electric actuators are DC motors having different maximum revolutions, two first and second driver circuits may be used for selectively driving the DC motors or a single common driver circuit may be used for selectively driving the two motors.

(7) When using a stepping motor having different drive currents, it is possible to provide a plurality of driver circuits corresponding to the number of excitation phases in the stepping motor. These driver circuits may also be used for driving different stepping motors.

Although the invention has been described with respect to specific illustrative examples, it will be appreciated by one skilled in the art that a variety of changes may be made without departing from the scope of the invention.