EP2166142A1

EP2166142A1 - Cloth cutting device of hole stitching machine

Info

Publication number: EP2166142A1
Application number: EP09170893A
Authority: EP
Inventors: Tsuguo Kubota
Original assignee: Juki Corp
Current assignee: Juki Corp
Priority date: 2008-09-22
Filing date: 2009-09-22
Publication date: 2010-03-24
Anticipated expiration: 2029-09-22
Also published as: KR20100033944A; DE602009000904D1; JP2010069205A; CN102021765A; EP2166142B1; CN102021765B; ATE502149T1

Abstract

A cloth cutting device (30) of a buttonholing machine (1) includes a knife (32), a knife receiver (31), a moving mechanism (35) which moves the knife (32) or the knife receiver (31), a pulse motor (34) which serves as a drive source of the movement of the knife or the knife receiver, a rotation amount detector (55) which detects a rotation amount of the pulse motor, and a controller (50) which controls the pulse motor. The controller executes a control to switch the movement of the knife or the knife receiver to be low speed on its way, and includes a cutting control means (50c) which controls the pulse motor to stop driving if a deviation determining means determines that the deviation of the pulse motor reaches the set value, and a current control means (50c) which limits, during the low-speed movement, a current value applied to the pulse motor to be lower than that during a high-speed movement.

Description

The present invention relates to a cloth cutting device of a buttonholing machine which forms a hole in a workpiece.
An eyelet buttonholing machine includes a sewing machine drive mechanism which moves a needle bar up and down and swings it to the right and left and actuates a looper mechanism in synchronization with the needle bar, a cloth feed mechanism which holds and feeds a cloth in the front-rear/right-left direction, and a turning mechanism which turns the needle bar and the looper mechanism. The eyelet buttonholing machine includes a cloth cutting mechanism which presses and cuts a cloth between a knife and a knife receiver, and is capable of forming a buttonhole inside an overlock stitching section by actuating the cloth cutting mechanism before or after forming the overlock stitches.
As a recent eyelet buttonholing machine, there is known an electronic eyelet buttonholing machine which can perform overlock stitching for a buttonhole having an optional shape by electrically controlling the respective driving of the sewing machine drive mechanism, the cloth feed mechanism, the turning mechanism, and the cloth cutting mechanism based on given data.
For example, as described in JP2001-334088A , the cloth cutting mechanism includes a cloth cutting control mechanism which uses a pulse motor as a drive source, and the cloth cutting control mechanism controls a drive amount (number of pulse outputs) and a driving speed (pulse output frequency) of the pulse motor for driving one of the knife and the knife receiver.
Moreover, for example, as described in JP2002-200377A , there is also known a buttonholing machine which into which data for correcting and setting a downward movement amount of the knife receiver is input and stored so as to switch the pressing force between the cloth cutting knife and the knife receiver depending on the thickness and the kind of cloth.
Meanwhile, the cloth cutting control mechanism using the pulse motor as a drive source drives the pulse motor by means of open loop control in general, so that the number of pulse outputs which enables application of an appropriate pressing force to the cloth needs to be set in advance in accordance with conditions such as the kind of cloth to be cut and the size of the buttonhole, etc. Therefore, an appropriate number of pulse outputs that is suitable for the conditions needs to be set through trial and error, which greatly deteriorates the working efficiency.
Further, because the actual level of the pressing force applied is uncertain only from the setting of the number of pulse outputs, the number of pulse outputs has generally been set, placing importance on cutting reliability, such that the pressing force becomes higher than the appropriate pressing force. Therefore, there has been a drawback that an excessive impact is applied to the knife, which damages the knife and shortens the life of the knife or the knife receiver. Further, there has been a problem that loss of synchronism of the pulse motor is caused.
In order to prevent such loss of synchronism of the pulse motor without losing the cycle time of cloth cutting, conventionally, control is performed in which the pulse motor is driven at a high speed to the vicinity of a position where the cloth cutting knife and the knife receiver are joined, and the driving is switched to a low speed from the vicinity of the joining position.
More specifically, there is a method in which a plurality of numbers of pulses in the low-speed section are stored as adjustment values, and for each of a plurality of knife receivers, or depending on conditions such as a material of the cloth, a suitable adjustment value is selected from the plurality of adjustment values.
However, when the buttonhole length, that is, the cloth cutting length is changed, as shown in Figs. 3A to 3C, the knife receiver needs to be replaced with a longer one in accordance with an increase in the cloth cutting length. Thus, due to an increase in a contact surface between the knife and knife receiver or a stress, a sufficient pressing force on the entire contact surface cannot be obtained. Accordingly, a change amount according to the cloth cutting length needs to be additionally considered in the adjustment amount, so that set values to be stored increase, which makes an accurate selection difficult.
Moreover, each time a portion of the knife receiver where it contacts the knife is worn as being used so that cutting sharpness is deteriorated, the knife receiving surface must be refined to be smooth. Therefore, the knife receiver face gradually becomes thin, so that a movement stroke of the knife receiver required to contact the cloth cutting knife changes, and as described above, each time the knife receiver is replaced, the movement distance often changes. Consequently, the adjustment amount needs to be set to a value in which the variation of the thickness of the knife receiver and a pushing-in amount for obtaining a pressing force suitable for the thickness and material of the cloth are taken into consideration, and thus, setting of a suitable value requires proficient skill.
It is an object of the present invention to provide a cloth cutting device which can easily obtain an appropriate pressing force without losing the cycle time.
A first aspect of the present invention provides a cloth cutting device of a buttonholing machine. The cloth cutting device comprises:

a knife having a cutting edge;
a knife receiver which presses a cloth so as to pinch the cloth in cooperation with the knife to cut the cloth;
a moving mechanism which moves one of the knife and the knife receiver toward and away with respect to the other;
a pulse motor which serves as a drive source of the toward and away movement of the knife or the knife receiver by the moving mechanism; and
a controller which controls the pulse motor such that, during the movement of the one of the knife and the knife receiver toward the other, the one of the knife and the knife receiver is moved at a predetermined low speed from a position before cutting, at which the cutting edge of the knife is in a vicinity of the knife receiver, to cut the cloth.

The controller comprises:

a current control means which limits, during the low-speed movement, a current value applied to the pulse motor to be lower than that during a high-speed movement;
a deviation determining means which determines, during the low-speed movement, whether a deviation between a value detected by the rotation amount detector and a value instructed to the pulse motor is a set value, which is set in advance, or more; and
a cutting control means which controls the pulse motor to stop the movement of the one of the knife and the knife receiver if the deviation determining means determines that the deviation is the set value or more.

According to a second aspect of the present invention, the current control means limits, during the low-speed movement, the current value applied to the pulse motor to be lower than a current value before the one of the knife and the knife receiver reaches the position before cutting.
According to a third aspect of the present invention, the cloth cutting device comprises a pressing force setting means which sets a pressing force for the cloth cutting, and a storing means which stores the pressing force set by the pressing force setting means. The current control means determines a limit value of a maximum current value in accordance with the pressing force stored in the storing means.
According to a fourth aspect of the present invention, the controller controls the current supply to the pulse motor so as to maintain the pressing force for the cloth cutting for a certain period of time after the cutting control means stops the movement of the one of the knife and the knife receiver.
According to the first aspect of the present invention, during the movement of the one of the knife and the knife receiver toward the other, the one of the knife and the knife receiver is moved at a predetermined low speed from the position before cutting at which the cutting edge of the knife is in the vicinity of the knife receiver. During the low-speed movement, the deviation determining means monitors the deviation between the value detected by the rotation detector and the motor instruction value. When the deviation reaches a predetermined value, the cutting control means stops the low-speed movement of the knife or the knife receiver. That is, depending on the deviation, the cloth cutting can be performed with a certain pressing force. Therefore, without a complicated setting operation for determining an appropriate knife adjustment value which requires proficient skill, an appropriate pressing force can easily be obtained. Further, in the case of this control, the movement of the knife or the knife receiver is controlled based on the deviation which is primarily caused by the hitting of the knife and knife receiver. Thus, even when there are variations in size and wearing amount for the respective knife receivers, the pressing force can be made the same.
Further, according to the first or second aspects of the present invention, the current control means reduces the current value to be supplied to the pulse motor during the low-speed movement, so that the output torque of the pulse motor is also reduced, which relieves the contact pressure at the time when the knife and knife receiver hit each other, and makes it possible to prevent mutual breakages of the knife and knife receiver and to avoid loss of synchronism of the motor.
According to the third aspect of the present invention, the limit value of the maximum current value is determined in accordance with the set value of the pressing force for the cloth cutting, so that a torque of the pulse motor can optionally be set. Thus, the pressing force of the knife or the knife receiver can precisely be set, and a more appropriate pressing force can be obtained.
According to the fourth aspect of the present invention, the pressing force for the cloth cutting, that is, the pressing force of the knife receiver to the knife is maintained for a certain period of time even after the low-speed movement of the knife or the knife receiver is stopped, so that it can wait until the cloth is cut with the elapse of time.
Other aspects and advantages of the present invention will be apparent from the following description, the drawings and the claims.
The following description of preferred embodiments of the invention serves to explain the invention in greater detail in conjunction with the drawings. These show:

Fig. 1:: a side view showing a general configuration of a sewing machine according to the embodiment;
Fig. 2:: a perspective view showing a general configuration of a cloth cutting device according to the embodiment;
Fig. 3A:: a top view of a knife and a small-sized knife receiver of the cloth cutting device;
Fig. 3B:: a top view of the knife and a medium-sized knife receiver of the cloth cutting device;
Fig. 3C:: a top view of the knife a large-sized knife receiver of the cloth cutting device;
Fig. 4:: a block diagram showing a control configuration of the sewing machine of Fig. 1;
Fig. 5:: a front view of an operation panel;
Fig. 6:: diagrams (A) to (D) showing changes of current values to be supplied to respective coils A, A', B, and B' per one pulse;
Fig. 7:: a chart showing detailed current values to be supplied to the respective coils A, A', B, and B' per one pulse of the pulse motor;
Fig. 8:: a diagram showing a torque characteristic of the pulse motor;
Fig. 9:: a diagram showing an A-phase signal and a B-phase signal of an encoder;
Fig. 10:: a chart showing correspondence relationship between output codes of 0 to 255 and current values to be supplied to the coil of the pulse motor 34 by a pulse motor drive circuit via a D/A converter;
Fig. 11:: a diagram (A) showing a torque change of the pulse motor after the knife receiver reaches the knife, and a diagram (B) showing a deviation after the knife receiver reaches the knife;
Fig. 12:: a flowchart showing a process of setting a pressing amount for driving; and
Fig. 13:: a flowchart showing a cloth cutting control to be performed by the cloth cutting device.

Overall Configuration of Eyelet Buttonholing Machine
As shown in Fig. 1, an eyelet buttonholing machine 1 including the cloth cutting device 30 (shown in Fig. 2) has a basic configuration as a sewing machine which performs eyelet buttonhole stitching. The eyelet buttonholing machine 1 includes a machine frame 5 which has a bed portion 2 having a substantially rectangular box shape, a vertical drum portion 3 provided on a rear portion of the bed portion 2, and an arm portion 4 provided to extend forward from an upper portion of the vertical drum portion 3, and a machine table on which the machine frame 5 is placed.
On a distal end portion of the arm portion 4, a needle bar 10 including a sewing machine needle 6 on a lower end portion is provided so as to extend downward and move up and down and swing to the left and right. On the bed portion 2, a looper base 11 including, on an upper portion, a looper portion 11 a opposed to the needle bar 10 and having a looper (not shown) and a spreader (not shown) which assists the looper is provided. Inside the machine frame 5, respective drive mechanisms (not shown) for moving the needle bar 10 up and down and to the left and right and driving the looper and spreader in synchronization with the needle bar 10 are provided.
On an upper surface portion of the bed portion 2, a feed base 18 (shown in a section in Fig. 1) on which a cloth is set is provided, and a pair of cloth pressers 19 for pressing a cloth is provided on an upper surface portion of the feed base 18. The feed base 18 has a thin rectangular box shape having an opened lower surface as a whole, and on an upper surface of the feed base 18, an opening which is positioned between the pair of cloth pressers 19 and is elongated in the front-rear direction is provided. This feed base 18 is moved horizontally by a feed mechanism (not shown) provided inside the bed portion 2.
In the eyelet buttonholing machine 1, a cloth cutting device 30 for opening an eyelet buttonhole in a cloth is provided. This cloth cutting device 30 will be described later. In the eyelet buttonholing machine 1, the cloth cutting device 30 forms an eyelet buttonhole in a cloth, and in synchronization with up and down movements and needle swinging operations of the needle bar 10, the looper is driven, and overlock stitches are formed around the eyelet buttonhole by cooperation of the sewing machine needle 6 and the looper.
Cloth Cutting Device
Next, the cloth cutting device 30 will be described. As shown in Fig. 2, the cloth cutting device 30 includes a knife receiver 31 (also shown in Fig. 1) corresponding to a shape of an eyelet buttonhole, a knife 32 which is disposed opposite the knife receiver 31 and has a cutting edge formed on an upper end portion, a drive shaft 33 provided rotatably, a pulse motor 34 for driving and rotating the drive shaft 33, and a moving mechanism 35 which moves the knife receiver 31 toward and away from the knife 32 by the rotation of the drive shaft 33. In Fig. 2, for simplifying the drawing, illustration of the major configuration portion of the eyelet buttonholing machine 1 is omitted.
The pulse motor 34 has a resolution of, for example, 400, and is provided fixedly inside the bed portion 2 on the vertical drum portion 3 side. This pulse motor 34 is provided with an encoder (rotation amount detector) 55 with a resolution of, for example, 400 for detecting the rotation amount of the pulse motor 34 (see Fig. 4). The output shaft of the pulse motor 34 is directed upward. A motor gear 36 using the output shaft of the pulse motor 34 as a rotation shaft is provided fixedly to the output shaft. Inside the vertical drum portion 3, a ball screw member 37 extending up and down is provided, and on the outer periphery of the ball screw member 37, a thread groove is formed. The ball screw member 37 is supported by a bearing (not shown) fixed to the bed portion 2 and the arm portion 4 rotatably around an axis of the bearing. Therefore, the ball screw member 37 is restrained from moving to the left and right and up and down, and is allowed to rotate only.
A gear 38 using a rotation shaft of the ball screw member 37 as a rotation shaft is provided fixedly to the lower end portion of the ball screw member 37, and this gear 38 engages with the motor gear 36. Therefore, when the pulse motor 34 is driven to rotate, the ball screw member 37 rotates.
A housing 39 is disposed inside the vertical drum portion 3, and a nut (not shown) is provided fixedly to the housing 39. The nut engages with the ball screw member 37. Accordingly, when the ball screw member 37 rotates, the housing 39 moves up and down. A shaft (not shown) extending up and down is provided fixedly inside the vertical drum portion 3, and this shaft penetrates through the housing 39, and the housing 39 is slidable up and down with respect to this shaft. Therefore, this shaft restrains rotation of the housing 39, so that the housing 39 smoothly moves up and down.
The housing 39 is provided with a link mechanism 40 including links 41 and 41 and a lever 42. The lever 42 is forked at its distal ends, and has a substantially Y shape. One end portions of the links 41 are joined to the distal ends of the lever 42, respectively, so as to become turnable around the rotation shaft in the extending direction of the arm portion 4. The other end portions of the links 41 are joined to the housing 39 so as to become turnable around the rotation shaft in the extending direction of the arm portion 4.
A drive shaft 33 extending in the extending direction of the arm portion 4 is provided inside the arm portion 4 so as to become turnable around the rotation shaft in the extending direction. A base end portion of the lever 42 is provided fixedly to the end portion on the vertical drum portion 3 side of the drive shaft 33. Therefore, when the pulse motor 34 is driven to rotate, the ball screw member 37 rotates, and in accordance with the rotation of the ball screw member 37, the housing 39 moves up and down. Then, in accordance with the up and down movement of the housing 39, the link mechanism 40 is actuated, and accordingly, the drive shaft 33 rotates.
The moving mechanism 35 includes a linear gear 44 provided on the other end portion of the drive shaft 33, and a linear shaft 45 which engages with the linear gear 44. The linear gear 44 is provided on the drive shaft 33 so as to use the rotation shaft of the drive shaft 33 as an axis. The linear shaft 45 extends in the up-down direction movably up and down with respect to the arm portion 4. On the outer periphery of the linear shaft 45, a rack portion 45a is formed, and this rack portion 45a engages with the linear gear 44. In other words, the moving mechanism 35 is a pinion rack mechanism, and the linear shaft 45 moves up and down in accordance with a rotation of the linear gear 44 together with the drive shaft 33. The linear shaft 45 projects downward of the arm portion 4 from the inside of the arm portion 4. The linear shaft 45 is supported on the arm portion 4 by a support member not shown, and this support member restrains the linear shaft 45 from moving leftward and rightward, moving forward and rearward, and rotating. Therefore, the linear shaft 45 can stably move up and down.
To the lower end portion of the linear shaft 45, a knife receiver 31 is attached in a replaceable manner. As shown in Fig. 2, to the bed portion 2, a knife 32 is detachably attached so as to be disposed opposite the knife receiver 31. The knife 32 has, as shown in Figs. 3A to 3C, one end portion 32 formed annularly and the other portion 32b formed linearly.
On the other hand, the knife receiver 31 has a shape which allows one end portion 32a and a part of the other end portion 32b of the knife 32 to be brought into contact with each other. Here, as the knife receiver 31, as shown in Figs. 3A to 3C, small-sized, medium-sized, and large-sized knife receivers having different contact lengths with the other end portion 32b of the knife 32 are available, and a knife receiver 31 having a size corresponding to a cloth cutting length is attached to the bed portion 2.
With the configuration described above, when the drive shaft 33 is rotated by the pulse motor 34, the knife receiver 31 moves up and down together with the linear shaft 45. Hereinafter, for simple description, it is assumed that when the pulse motor 34 is driven to rotate forward, the knife receiver 31 moves down toward the knife 32, and when the motor is driven to rotate in reverse, the knife receiver 31 moves up in a direction of separating from the knife 32. The forward and reverse rotations of the pulse motor 34 and the upward and downward movements of the knife receiver 31 may be inverted.
In the cloth cutting device 30, when a cloth is interposed between the knife receiver 31 and the knife 32 which are separated from each other, the pulse motor 34 rotates forward and the knife receiver 31 moves down to the knife 32, and a pressing force for the cutting is applied to the cloth pinched between the knife receiver 31 and the knife 32. Thereafter, the pulse motor 34 is further driven to rotate forward and the knife receiver 31 presses the knife 32. Therefore, the knife receiver 31 presses the cloth so as to pinch the cloth in cooperation with the knife 32, and by the fitting of the knife receiver 31 and the knife 32, the cloth is cut. Then, when an eyelet buttonhole is formed in the cloth, the pulse motor 34 is driven to rotate in reverse, and the knife receiver 31 moves up. The knife receiver 31 continuing to move up stops at an origin position which is the highest moving-up position of the knife receiver 31 when an origin position sensor not shown is turned ON.
Control System of Sewing Machine
Fig. 4 is a block diagram showing a main control configuration of the eyelet buttonholing machine 1. As shown in Fig. 4, the eyelet buttonholing machine 1 is provided with a controller 50 which controls operations of the cloth cutting device 30 as well as operations of the eyelet buttonholing machine 1. The controller 50 includes a main shaft motor drive circuit 51b for driving a main shaft motor 51a of the sewing machine, an I/F 51c for connecting the drive circuit 51b to a CPU 50c of the controller 50, an X-axis motor drive circuit 52b for driving an X-axis motor 52a provided in the feed mechanism, an I/F 52c for connecting the drive circuit 52b to the CPU 50c, a Y-axis motor drive circuit 53b for driving a Y-axis motor 53a provided in the feed mechanism, an I/F 53c for connecting the drive circuit 53b to the CPU 50c, a turning motor drive circuit 54b for driving a turning motor 54a which turns the needle bar 10 and the looper portion 11 a, an I/F 54c for connecting the drive circuit 54b to the CPU 50c, a pulse motor drive circuit 60 for driving a pulse motor 34, an A-phase D/A converter 70 for analog-converting current instruction values for an A-phase and an A'-phase of the pulse motor 34 and outputting these to the drive circuit 60, an I/F 80 for connecting the A-phase D/A converter 70 to the CPU 50c, a B-phase D/A converter 71 for analog-converting current instruction values for a B-phase and a B'-phase of the pulse motor 34 and outputting these to the drive circuit 60, an I/F 81 for connecting the B-phase D/A converter 71 to the CPU 50c, an encoder circuit 55b for counting a count value of an encoder 55, an I/F 55c for connecting the encoder circuit 55b to the CPU 50c, an operation panel 57 into which various settings are input, and an I/F 57c for connecting the operation panel 57 to the CPU 50c.
The controller 50 includes a ROM 50a in which various control programs and data to be used in the programs are stored, a RAM 50b and an EEPROM 50d in which data read from the ROM 50a, data input or set from the operation panel 57 and data, etc., calculated by a CPU 50c described later based on the programs are stored, and the CPU 50c which performs various processings based on the programs.
Fig. 5 is a front view of the operation panel 57. The operation panel 57 includes a display area 57a for displaying pattern numbers for selecting various buttonholing shapes and an increase/decrease key 57b for making the selection, a display area 57c for displaying which of pattern data including set values of sizes, etc., individually set for the respective patterns is selected and an increase/decrease key 57d for making the selection, a display area 57e for displaying an item number of a set item selected for the selected pattern data and an increase/decrease key 57f for making a selection of the item number of the set item, a knife adjustment key 57g for inputting a pressing amount for cloth cutting driving by the pulse motor 34, and a ready key 57h for making a ready state for a buttonholing operation.
Here, in setting of a pressing amount for the cloth cutting driving by the knife adjustment key 57g, a ratio (%) of the pressing amount can be set in the range of 10 to 100% in, for example, ten stages.
By the function described above, the operation panel 57 functions as a pressing force setting means for setting a pressing force for the cloth cutting (pressing amount for the cloth cutting driving). The pressing amount for cloth cutting driving set and input from the operation panel 57 is stored in the EEPROM 50d as a storing means.
With the configuration described above, from the operation panel 57, when a pattern and pattern data of a buttonholing shape are selected, contents of the set item are settled, and the ready key 57h is pressed down and sewing starts, first, a cloth as a workpiece is moved to a sewing start position by driving of the X-axis and Y- axis motors 52a and 53a, and buttonhole stitching is started by driving of the main shaft motor 51a. In this buttonhole stitching, when a needle swinging stitching is performed along one side of a position at which a straight portion of a buttonhole is planned to be formed, and when an eyelet buttonhole is formed, overlock stitches are formed along the periphery of the eyelet buttonhole by driving the turning motor 54a at a position at which an eyelet buttonhole is planned to be formed. Then, the needle swinging stitching is performed along the side opposite to the sewing start of the straight portion of the buttonhole, and depending on the setting, bar tacking is performed at an end portion, and sewing is finished. Further, the cloth is conveyed to a cutting position in the cloth cutting device 30, a buttonhole is formed by driving of the pulse motor 34, and the series of sewing operations are completed. The cutting operation is performed prior to sewing depending on setting. The control of the cutting operation will be described in further detail later.
Control Configuration of Cloth Cutting Device
Here, the control configuration of the cloth cutting device 30 will be described in further detail.
The above-described CPU 50c performs control of the operation of the whole eyelet buttonholing machine 1, and also executes control of the cloth cutting device 30 as a part of the control of the whole eyelet buttonholing machine 1. In other words, the CPU 50c also functions as a controller of the cloth cutting device 30.
Cloth Cutting Device: Pulse Motor
The pulse motor 34 is a two-phase bifilar wound motor, and includes A-phase and B-phase coils, and A'-phase and B'-phase coils which are reversely wound with respect to the A-phase and B-phase coils.
The A-phase D/A converter 70 and the I/F 80 thereof are provided for the A-phase and A'-phase coils, and the B-phase D/A converter 71 and the I/F 81 thereof are provided for the B-phase and B'-phase coils.
The pulse motor 34 controls one rotation by switching A-, A'-, B-, and B'-phase currents with a resolution of 400 pulses from the CPU 50c. Fig. 6(A) to Fig. 6(D) are diagrams showing changes of current values to be supplied to the coils A, A', B, and B' per one pulse with respect to the rotation position of the pulse motor 34, and Fig. 7 is a chart showing detailed current values Ai, A'i, Bi, and B'i to be supplied to the coils A, A', B, and B' per one pulse and codes Ac and Be (digital values) to be output respectively to the A-phase D/A converter 70 and the B-phase D/A converter 71 from the CPU 50 for supplying the current values, on the basis of respective rotation positions of the pulse motor 34 at (1) to (8) of Fig. 6. For example, when the pulse motor 34 is driven with a resolution of 400 pulses, by switching the current from (1) to (2), the pulse motor 34 rotates by 0.9 degrees forward.
As illustrated, as changes of the current values to be supplied to the coils changes of one period in the range from -5 to +5 [A] are shown per 8 pulses, and the changes of the current values to be supplied to the coils A, A', B, and B' are supplied so as to delay by 1/4 phase in order. To the A' and B' phases, in actuality, the current values of A and B phases are respectively inverted in polarity and supplied.
By supplying the above-described currents to the coils A, A', B, and B', the pulse motor 34 is driven by 1-2 phase excitation (half-step driving).
Next, a torque characteristic of the pulse motor 34 will be described with reference to the torque characteristic diagram of Fig. 8. Here, the electric angle τ represents one period (8 pulses) of the A/B phase, and when the rotor of the motor delays by 2 pulses (τ/4) with respect to an instruction value, a maximum torque maxT is generated, and when the rotor delays by 4 pulses, loss of synchronism occurs.
The maximum torque maxT is a torque when the current value is supplied periodically in the range from -5 to +5 [A] per 8 pulses. The torque to be obtained from the pulse motor 34 is determined in proportion to the amplitude of the periodic current value.
Cloth Cutting Device: Encoder and Encoder Circuit
The encoder 55 of the pulse motor 34 is an incremental type, and an A-phase signal and a B-phase signal which include 400 pulses are output by shifting by a 1/4 phase per one rotation. Fig. 9 shows the A-phase signal and the B-phase signal of the encoder 55. The encoder circuit 55b performs counting by multiples of 4 by counting both rise and fall edges of the pulses of the A-phase signal and the B-phase signal, as illustrated. Therefore, the encoder 55 can obtain a count value (resolution) 4 times the number of output pulses. Each time the pulse motor 34 is driven by one pulse, the encoder increments (or decrements) by four counts. Therefore, the CPU 50c can detect the rotation position of the pulse motor 34 with a resolution of 1600 counts per one rotation of the pulse motor 34. Therefore, when the drive current for the pulse motor 34 is switched from (1) to (2) of Fig. 6, it is detected as a rotation amount of 4 pulses.
By reading the count value of the encoder circuit 55b, the CPU 50c can detect the position of the pulse motor 34.
Cloth Cutting Device: D/A Converter and Pulse Motor Drive Circuit
One A-phase D/A converter 70 is provided and shared by the A-phase coil and A'-phase coil, and one B-phase D/A converter 71 is provided and shared by the B-phase coil and the B' phase coil. In the following description, the converter for the side of the A-phase coil and the A'-phase coil is described, and the other converter for the B-phase coil and the B'-phase coil have the same configuration except that the phase of current supply delays by a half phase.
The CPU 50c calculates, depending on a current excitation state (any position of (1) to (8) in Fig. 7), D/A values in an excitation state where excitation is advanced. In this cloth cutting device 30, a supply current value can be controlled in the range of 0 to 100% according to a set pressing amount for cloth cutting driving, which is set in advance, so that to the A-phase D/A converter 70 and the B-phase D/A converter 71, values obtained by multiplying the calculated D/A values by a pressing amount are output when cutting a cloth.
The A-phase D/A converter 70 outputs an analog signal (0, 0.02, 0.04, 0.06, ..., 4.98, 5.00 [V]) dividing the range of 0 to 5 [V] into 256 stages to the pulse motor drive circuit 60 when it receives codes of 0 to 255 from the I/F 80.
On the other hand, the pulse motor drive circuit 60 supplies current values which divide the range of -5 to +5 [A] into 256 stages and corresponds to the analog signal to the coils of the pulse motor 34.
Fig. 10 is a chart showing correspondence between output codes of 0 to 255 of the I/F 80 and current values to be supplied to the coils of the pulse motor 34 by the pulse motor drive circuit 60 via the A-phase D/A converter 70.
When the pressing amount for cloth cutting driving is 100%, as shown in Fig. 7, current values of +5.00, +3.54, -3.54, -5.00, -3.54, 0, and +3.54 must be supplied to the A-phase coil in order, so that codes corresponding to these are output in order from the CPU 50c, and when the pressing amount for cloth cutting driving is set to a value other than 100%, codes corresponding to values multiplied by a setting ratio are output from the CPU 50c.
As described above, the A'-phase coil shares the I/F 80, the A-phase D/A converter 70 and the pulse motor drive circuit 60 with the A-phase coil, however, the pulse motor drive circuit 60 is constructed to supply a current with polarity reverse to that of the A-phase coil to the A'-phase coil in response to an output code from the I/F 80. The same applies to the I/F 81, the B-phase D/A converter 71, and the pulse motor drive circuit 62 for the B-phase and B'-phase coils.
The pulse motor drive circuit 60 includes a switching element (transistor, FET, etc.) for respective current supply/cut-off to the A-phase coil and the A'-phase coil, a detection circuit which detects voltages in proportion to current values supplied to the coils, an amplifier which compares a detected voltage of each coil and an analog signal from the A-phase D/A converter 70, and a PWM output circuit which increases and decreases a current supply ON/OFF control ratio of the switching element in accordance with an output of the amplifier. Accordingly, the switching element performs current supply/cut-off at an ON/OFF ratio corresponding to the analog signal from the A-phase D/A converter 70, and current supply to each coil is performed with a planned effective current value. The same applies to the B-phase D/A converter 71 for the B-phase and B'-phase coils.
Cloth Cutting Device: Cloth Cutting Control by CPU
When the knife receiver 31 moves toward the knife 32 from a standby position for the cloth cutting in accordance with a cloth cutting control program stored in the ROM 50a, the CPU 50c controls the operation of the pulse motor 34 so as to move the knife receiver 31 at a high speed to a position before cutting at which the cutting edge of the knife 32 is in the vicinity of the knife receiver 31, and to move the knife receiver 31 at a predetermined low speed slower than the high speed from the position before cutting by switching the speed to cut a cloth. Here, "the position before cutting" means a height set so as to have a certain margin that prevents collision between the knife 32 and the knife receiver 31 even when these have individual differences and attaching errors, while the knife receiver 31 is in the vicinity of the knife 32.
The speed control of the pulse motor 34 is executed by changing the output period of an instruction pulse for the pulse motor 34. In the high-speed movement section, regardless of the set value of the pressing amount for cloth cutting driving, a numerical signal is output so that the current value to be supplied to each coil of the pulse motor 34 becomes 100%.
By the above-described control, the CPU 50c functions as "movement control means" (controller) in cooperation with the A-phase D/A converter 70, the B-phase D/A converter 71, and the pulse motor drive circuit 60.
According to the cloth cutting control program stored in the ROM 50a, in the low-speed section from the position before cutting, while performing position control of the pulse motor 34 so as to advance the excitation position, the CPU 50c calculates a deviation between an excitation position indicated by an instruction pulse of the pulse motor 34 and a detected position indicated by the encoder 55, and determines whether this deviation exceeds 8 counts determined in advance as a count value of the encoder 55. In other words, the CPU 50c functions as a deviation determining means. The deviation of 8 counts as a count value of the encoder 55 corresponds to a delay of 2 pulses in the pulse motor 34, and as described in Fig. 8, generates a maximum torque maxT. When the CPU 50c calculates the deviation between an instruction pulse of the pulse motor 34 and the detected position indicated by the encoder 55, the number of pulses for one-rotation driving of the pulse motor 34 and the number of pulses detected when the encoder 55 makes one rotation are 400 and 1600, respectively, so that to make these numbers of pulses correspond with each other, the CPU 50c sets the number of pulses 4 times the number of pulses for driving the pulse motor 34 as an instruction value to calculate the deviation.
Further, when the CPU 50c determines that the deviation exceeds 8 counts in the determination of the deviation described above, the CPU 50c controls driving of the pulse motor 34 so as to stop the low-speed movement of the knife receiver 31. By this control, the CPU 50c functions as a cutting control means.
Through the above-described control, the CPU 50c functions as a "cutting control means" in cooperation with the A-phase D/A converter 70, the B-phase D/A converter 71, and the pulse motor drive circuit 60.
Further, the CPU 50c executes torque control for limiting a driving torque of the pulse motor 34 in accordance with a set value of the pressing amount for cloth cutting driving in the low-speed section. In other words, in principle, the CPU 50c calculates the deviation between an excitation position indicated by an instruction pulse of the pulse motor 34 and a detected position indicated by the encoder 55, determines a driving torque from the deviation based on PID operation, and performs control for supplying current values corresponding to the driving torque to the coils. However, in the low-speed section, current values (current values based on a set torque) obtained by multiplying amplitude current values in the range of -5 to +5 [A] by a setting ratio of the pressing amount for cloth cutting driving are calculated, and when the current values based on the PID operation exceeds current values based on the pressing amount for cloth cutting driving, control for supplying the current values based on the pressing amount for cloth cutting driving to the coils is performed.
By the above-described control, the CPU 50c functions as a "current control means" in cooperation with the A-phase D/A converter 70, the B-phase D/A converter 71, and the pulse motor drive circuit 60.
Fig. 11(A) shows a torque change of the pulse motor 34 after the knife receiver 31 reaches a pressing start position at which application of a pressing force for the cutting to a cloth placed on the knife 32 becomes possible, and Fig. 11(B) is a diagram showing deviations after the knife receiver 31 reaches the pressing position. In the drawings, the horizontal axis indicates time, the symbol Tc in the drawings indicates a timing at which the knife receiver 31 reaches the above-described pressing start position, and the symbol Ts indicates a torque value based on a set pressing amount for cloth cutting driving.
As shown in the drawings, before the knife receiver 31 reaches the pressing start position, no load is applied, so that a deviation is hardly caused. Therefore, the pulse motor 34 is driven with a driving torque necessary for low-speed driving as a torque value. When the knife receiver 31 reaches the pressing start position, a load is applied to the pulse motor 34 and the rotation speed is reduced, so that the delay (deviation P) of the rotation position with respect to the instruction pulse, the time delay (I), and the deviation change amount (D) increase, respectively. Therefore, the calculated value by the PID operation calculated by the CPU 50c increases, and a necessary torque calculated from the calculated value by the PID operation increases. Thereafter, when the deviation increases to 8 counts, the pulse motor 34 outputs a maximum torque, however, in this process, when the driving torque based on the PID operation exceeds the torque based on the set pressing amount for cloth cutting driving, the pulse motor is controlled so as not to output a torque higher than the torque based on the set pressing amount for cloth cutting driving.
Accordingly, after the cloth is cut, even when the knife receiver 31 hits the knife 32 and further presses it, currents exceeding the current values based on the set pressing amount for cloth cutting driving are not supplied to the coils, and the contact pressure and pressing force when the knife receiver 31 and the knife 32 hit each other can be limited.
Cloth Cutting Control
Control of the cloth cutting device 30 will be described.
First, as a premise of execution of cloth cutting, processing for setting a pressing amount for cloth cutting driving will be described based on the flowchart shown in Fig. 12.
First, when an operator turns the knife adjustment key 57g on the operation panel 57 on, knife adjustment setting processing is started. First, the CPU 50c displays a current pressing amount for the cloth cutting driving in percentage on the display area 57c in response to pressing-down of the knife adjustment key 57g (Step S1).
Next, it is determined whether an input has been made from the increase/decrease key 57d (Step S2), and if no input is made, the process is advanced to Step S4, and if an input is made, in accordance with this input, the value of the current pressing amount is increased or decreased, and the increased/decreased value is displayed on the display area 57c (Step S3), and then the process is advanced to Step S4.
At Step S4, the CPU 50c determines whether an input has been made from the knife adjustment key 57g, and if no input is made, the CPU 50c returns the process to Step S2, and if an input is made, the CPU 50c fixes the increased or decreased pressing amount for cloth cutting driving, and updates the data stored in the EEPROM 50d and finishes the setting processing (Step S5).
Next, cloth cutting control by the cloth cutting device 30 will be described with reference to the flowchart of Fig. 13.
When the sewing process reaches the cloth cutting process, cloth cutting control is started. In this cloth cutting control, first, the CPU 50c outputs an instruction pulse to each coil of the pulse motor 34 with a period corresponding to a determined in advance high speed so that the knife receiver 31 moves down to the position before cutting at the determined in advance high speed from the standby position (origin position)(Step S11). At this time, the CPU 50c outputs a forward rotation direction signal, and a pressing amount is output at 100% regardless of a set value. In other words, in a high-speed section at this movement start, current supply to the coils of the pulse motor 50c is performed with an amplitude of -5 to +5 [A].
Next, when the knife receiver 31 reaches the position before cutting at which the knife receiver 31 is in the vicinity of the cutting edge of the knife 32, the CPU 50c switches the output period of the instruction pulse so that the rotation of the pulse motor 50c is switched to a speed lower than the previous speed (Step S12). Thus, as described above, by moving the knife receiver 31 at a high speed up to the position before cutting, in comparison with the case where the knife receiver 31 is driven at a low speed in the whole section until the cloth is cut, the cycle time can be improved.
Next, the CPU 50c calculates a deviation between the instruction pulse and a detection signal from the encoder 55 (Step S13).
Then, the CPU 50c determines whether the deviation amount is 8 or more as a count value of the A- and B-phase signals of the encoder 55 (Step S14).
When the deviation is less than 8, the CPU 50c performs PID operation to calculate a necessary driving torque (Step S15). Further, the CPU 50c compares a set torque (value obtained by multiplying a torque of the pulse motor 34 when currents of -5 to +5 [A] are supplied to the coils by the set value of the pressing amount) calculated based on the set value of the pressing amount and a driving torque calculated by the PID operation (Step S16), and when the driving torque exceeds the set torque, the CPU 50c sets the torque of the pulse motor 34 not to the driving torque calculated by the PID operation but to the set torque so as to prevent the torque of the pulse motor 34 from exceeding the set torque (Step S17). Then, the CPU 50c outputs an instruction pulse of the pulse motor 34 and a numerical signal indicating the pressing amount for driving so that the pulse motor 34 is driven with the set torque, and accordingly, the A-phase D/A converter 70 and the B-phase D/A converter 71 output an analog signal which become a limited set torque value, and the pulse motor drive circuit 60 supplies current values limited in accordance with the set torque to the coils of the pulse motor 34 (Step S 18).
On the other hand, at Step S16, when the driving torque is not more than the set torque, an instruction pulse is output while the numerical signal indicating the pressing amount for torque driving is left at 100%, and the pulse motor drive circuit 60 supplies 100% current values to the coils of the pulse motor 34 in accordance with the driving torque (Step S18).
Then, the CPU 50c waits for 1 [ms] and repeats the processes from Step S13. In other words, the CPU 50c repeats the processes of Step S13 to Step S19 in a period of 1 [ms].
On the other hand, in the processing of Step S 14, when the deviation between the instruction pulse and the detection signal from the encoder 55 becomes 8, the knife receiver 31 reaches the knife 32 and cannot move up and down any further, and the current supply to the coils is maintained for 50 [ms] while keeping the excitation position of the pulse motor 34 (Step S20), and accordingly, the pressing force for the cloth cutting, that is, the pressing force of the knife receiver 31 to the knife 32 with the set pressing amount is maintained for 50 [ms] so that it can wait until the cloth is cut with the elapse of time.
Thereafter, the CPU 50c outputs an instruction pulse to make the speed as high as the speed at the time of the cloth cutting start, outputs a reverse rotation direction signal, and outputs a 100% pressing amount. Accordingly, the knife receiver 31 moves up to the standby position at a high speed (Step S21).
In the cloth cutting device 30 of the present embodiment, the CPU 50c functions as a deviation determining means and a cutting control means, monitors the deviation between a detected value of the encoder 55 and a motor instruction value, and stops the pressing movement of the knife receiver 31 when the deviation amount reaches 8 counts, so that cloth cutting can be performed with a fixed pressing force based on the deviation, and without skilled and complicated setting operations for determining an appropriate knife adjustment value, an appropriate pressing force can be easily obtained. In this control, the movement control is performed mainly based on a deviation caused by the hitting of the knife 32 and the knife receiver 31, so that even when knife receivers 31 have individual variations in size and wearing amount, the pressing force can be fixed.
Further, the CPU 50c functions as a current control means and reduces the current values to be supplied to the pulse motor 34 in the low-speed section, so that the output torque of the pulse motor 34 is also reduced, the contact pressure when the knife and knife receiver hit each other is reduced, mutual breakage of the knife and knife receiver is prevented, and loss of synchronism of the motor can be avoided.
The limit value of the current value of the pulse motor 34 is determined from the operation panel 57 in accordance with the set value of the pressing force for the cloth cutting, so that the torque of the pulse motor 34 can optionally be set, the pressing force of the knife or the knife receiver can precisely be set, and therefore, a more appropriate pressing force can be obtained.
Modified Examples
In the cloth cutting device 30 described above, a 2-phase pulse motor is used as the pulse motor 34, however, a 5-phase pulse motor, a 3-phase pulse motor, etc., may also be used. The driving method is half-step driving, however, full-step driving or micro-step driving may also be applied.
The encoder 55 is used as a rotation amount detector of the pulse motor 34, however, a resolver, a tachogenerator, or the like, which can detect a rotation amount, may also be used.
Further, the resolution of the encoder 55 is not limited to 400.
The outputs of the A-phase D/A converter 70 and the B-phase D/A converter 71 are not limited to 256 gradations.
Further, the pressing amount from the operation panel 57 is set as a ratio (%) to the maximum pressing force, however, it may appropriately be changed to a current value or a torque value to be directly set.
The cloth cutting device 30 is structured so that the knife receiver 31 moves up and down, however, the cloth cutting device 30 may also be structured so that the knife 32 moves up and down.
In the embodiment of the present invention, by moving the knife receiver 31 down at a high speed to a position before cutting at which the cutting edge of the knife 32 is in the vicinity of the knife receiver 31, and then moving the knife receiver 31 down at a low speed, the cycle time is improved in comparison with the case where the knife receiver 31 is driven at a low speed in the whole section, however, as a matter of course, the knife receiver 31 may be driven at a low speed in the whole section.
In the embodiment of the present invention, a case where the cloth cutting device 30 is applied to the eyelet buttonholing machine 1 is shown by way of example, however, the model and type of the sewing machine are not limited to the eyelet buttonholing machine as long as it is used for cutting a workpiece by pressing a knife and a knife receiver against each other.

Claims

A cloth cutting device (30) of a buttonholing machine (1), the cloth cutting device (30) comprising:
a knife (32) having a cutting edge;

a knife receiver (31) which presses a cloth so as to pinch the cloth in cooperation with the knife (32) to cut the cloth;

a moving mechanism (35) which moves one of the knife (32) and the knife receiver (31) toward and away with respect to the other;

a pulse motor (34) which serves as a drive source of the toward and away movement of the knife (32) or the knife receiver (31) by the moving mechanism (35); and

a controller (50) which controls the pulse motor (34) such that, during the movement of the one of the knife (32) and the knife receiver (31) toward the other, the one of the knife (32) and the knife receiver (31) is moved at a predetermined low speed from a position before cutting, at which the cutting edge of the knife (32) is in a vicinity of the knife receiver (31), to cut the cloth,
characterized by further comprising a rotation amount detector (55) which detects a rotation amount of the pulse motor (34),
wherein the controller (50) comprises:
a current control means (50c) which limits, during the low-speed movement, a current value applied to the pulse motor (34) to be lower than that during a high-speed movement;

a deviation determining means (50c) which determines, during the low-speed movement, whether a deviation between a value detected by the rotation amount detector (55) and a value instructed to the pulse motor (34) is a set value, which is set in advance, or more; and

a cutting control means (50c) which controls the pulse motor (34) to stop the movement of the one of the knife (32) and the knife receiver (31) if the deviation determining means (50c) determines that the deviation is the set value or more.
The cloth cutting device (30) according to claim 1, wherein the current control means (50c) limits, during the low-speed movement, the current value applied to the pulse motor (34) to be lower than a current value before the one of the knife (32) and the knife receiver (31) reaches the position before cutting.
The cloth cutting device (30) according to claim 1, the cloth cutting device (30) comprises a pressing force setting means (57) which sets a pressing force for the cloth cutting, and a storing means (50d) which stores the pressing force set by the pressing force setting means (57), wherein the current control means (50c) determines a limit value of a maximum current value in accordance with the pressing force stored in the storing means (50d).
The cloth cutting device (30) according to any one of claims 1 to 3, the controller (50) controls the current supply to the pulse motor (34) so as to maintain the pressing force for the cloth cutting for a certain period of time after the cutting control means (50c) stops the movement of the one of the knife (32) and the knife receiver (31).