GB2121983A - Control of a sewing machine for automatic sewing of patterns - Google Patents

Abstract

A sewing machine for automatic sewing of patterns comprises a fabric clamp arranged for movement in any direction under the needle of the machine, and an electronic control system for controlling the operative cycle of the clamp. The control comprises a servosystem of the feedback type comprising incremental encoder transducers, the pulses of which, properly elaborated, enter a combinatory logic circuit (108-120) and then a counter (122) which, interfaced with a microcomputer (100), effects detection of the clamp position and the closing of a position loop, a speed loop and a current loop being provided concentric with the position loop. The servosystem is used with D.C. moving coil type motors having a torque/inertia ratio which is greater than in other types of motor, so that angular accelerations of 30,000 rad/sec<2> can be achieved. <IMAGE>

Description

SPECIFICATION Control of a sewing machine for automatic sewing of patterns The present invention relates to a sewing machine provided with pattern control means to enable automatic sewing of patterns by the machine, for example sewing of a pattern on a piece of fabric stretched on a clamp and moving on a work plane in any direction obtained by the combination of two orthogonal movements.

The points of the fabric to follow one another under the sewing needle of the machine are defined by cartesian co-ordinates stored as data in a memory from which they are recalled and transferred, after appropriate processing, as drive signals to two D.C. motors which drive corresponding guides along cartesian orthogonal axes X and Y. Two types of devices are known in the art for achieving this task.

In the first type, an open loop control system is used, in which the data stored in the memory determines the sequence of the required movements and there are no feedback circuits to verify if the positions specified in the data have been reached.

In the second type, a closed loop control system is used, in which a signal corresponding to the actual position reached by the controlled element is continuously compared with a signal corresponding to the required position until cancellation of any difference therebetween, thus when the actual position is equal to the required position.

Against the advantage of a greater simplicity of the device of the first type, the possibility is provided by the device of the second type of varying the speed with which the required position is attained.

By appropriate construction of the feedback circuit, very short response times may be obtained, which is necessary when the sewing machine is arranged to operate at high sewing speeds, for example 2000 stitches/min, and when the movement of the fabric must begin only when the sewing needle has been withdrawn from the fabric and is in its upward stroke, so as to avoid collision of the fabric with the needle and consequent disruption of the sewing operation.

With such short response times, the exact positioning of the fabric for each stitch to be sewn requires a precise control of the displacement of the fabric.

According to the present invention there is provided a sewing machine provided with pattern control means to enable automatic sewing of patterns by the machine, the pattern control means comprising fabric retaining means displaceable in a work plane in any direction relative to sewing means of the machine by displacing means, and an electronic control device to control operation of the displacing means in dependence on a signal feedback therefrom, the control device comprising loop means including incremental encoder transducer means for providing signal pulses in dependence on displacement of the displacing means, logic circuit means to combine the pulses to provide signals indicative of the operation of the displacing means, counting means to determine the instantaneous position of the retaining means from such signals, and a microprocessor interfaced with the counting means for comparison of the determined instantaneous position with a required position to enable corresponding control of the displacing means by way of the logic circuit means, the loop means comprising a position loop for the position of the retaining means and a displacement speed loop and a current loop both concentric with the position loop.

In a preferred embodiment, displacement of the fabric retaining means, for example a clamp, is controlled by a servo-system of the feedback type comprising transducers of the incremental encoder type, the pulses of which, properly elaborated, enter a combinatory logic circuit and then a counter which, interfaced to a microcomputer, consents the detection of the position and the closing of the loop, where a speed loop and a current loop are provided, concentric to the position loop.

An embodiment of the present invention will now be more particularly described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a plan view of the mechanical driving system of the fabric clamp in a sewing machine embodying the invention; Fig. 2 is a sectional front elevational view of the driving system of Fig. 1; Fig. 3 is a general schematic block diagram of the control arrangement for the sewing machine; Fig. 4 is a circuit diagram of a low power section of the control arrangement; Fig. 5 is a circuit diagram of a high power section of the control arrangement; and Fig. 6 is a diagram of control signals for the closing of a position loop of the control arrangement.

Referring now to the drawings, Fig. 3 shows a control arrangement in which fabric displacement slides and a sewing head 10 are components of a complex two axis numerical control device with a third axis not operated by a central unit 12 of a control system of the arrangement.

This third axis, defined by movement of the sewing head 10, which has a motor independently controlled by a separate servo, exchanges signals with the central unit 12 (for control of the needle bar position and other functions) so as to allow correct synchronization of the movements on the two main axes of the displacement slides. The central control unit 12 is also associated with a further peripheral unit 14 for control of "auxiliary functions". Such auxiliary functions comprise output functions from the central unit, such as operation of an electromagnetic valve for opening of a fabric clamp carried by the displacement slides, and a working command of a cycle counter for the control system.The auxiliary functions also include input functions to the central unit, such as a "broken thread" signal from a mechanical sensor on the sewing head, a "presser foot down" signal from a microswitch, a "frame down" signal from a further microswitch, which prevents sewing when the clamp is open, an "overflow" signal from the cycle counter, "stroke end" signals (two for each axis), and absolute zero signals (one for each axis) provided by further microswitches.

The displacement slides are displaced by motors represented by the two blocks 16 and 18 in Fig. 3, relating to displacement in the two axes X and Y. The motors are exactly alike and are each formed by a D.C. motor of the moving coil type, in which the ratio between torque and inertia is greater than in other types of motor, so that angular accelerations of 30,000 rad/sec2 can be achieved. Connected to the motors are two incremental encoders with the function of position transducers. These transducers are not described in detail, as they can be of a kind usual in the art.

With reference to Figs. 1 and 2, the fabric clamp is schematically indicated by the numeral 30 and is arranged for carrying out translatory movement under the needle of the sewing machine. Displacement of the clamp 30 is effected, in one axis, by a first D.C. motor 34 mounted on a support plate 36. The output shaft of the motor 34 carries a pinion 35 coupled to a gear 38 mounted in turn on a shaft 40, on which there is fixed a pulley 42. A belt 44 engages the pulley 42 and another pulley 46 idle mounted on the support plate 36. A first slide is fixed to and displaceable by the beit 44 and is guided on two shafts 50 and 52 by a bush 54 and small wheels 56 respectively.

Displacement of the clamp 30 in the direction of the other axis is by way of a second D.C. motor 58, which is also fixed to the plate 36 and which drives the shaft 50 via a pinion (not illustrated) and a gear 60 fixed to the shaft 50. Two belts 62 and 64 are coupled to, respectively, two pulleys 66 and 68 which are fixed to the ends of the shaft 50. The belts 62 and 64 are also coupled to, respectively, two pulleys 70 and 72 idle mounted at the ends of the shaft 52. A rod 74 is fixed at its ends to the two belts 62 and 64 and is coupled to a second slide 76 so as to guide this slide and allow it to move in the direction in which the first slide 48 moves (Fig. 2).

The second slide 76 is slidably mounted on a shaft 78 and is prevented from rotating about the axis of this shaft by two shafts 80 parallel thereto.

The shaft 78 and the shafts 80 are fixed on the first slide 48 in such a way that when the rod 74 is displaced by the belts 62 and 64, the second slide 76 moves perpendicular to the direction of movement of the first slide 48. The fabric clamp 30, fixed by means of the arm 82 to the second slide 76, may thus translate along a system of orthogonal axes X and Y due to the combined effect of the two motors 34 and 58 and associated drive transmission.

In order to prevent movement of the clamp 39 beyond permitted limits, control microswitches 84 operable by followers 86 are provided.

Two further microswitches 88 have the task of establishing the zero position of the clamp 30, as will be described hereinafter.

A more detailed description of the control system for the clamp 30 will now be provided with reference to Fig. 4, which shows the low power section of the system.

Control of the entire system is by way of a single chip microprocessor 100 having a memory 102 of the EPROM type in which a "main" program is stored. A register 104 accedes both the memory 102 and a second EPROM memory 106, the latter being mounted on a command panel of the machine (not shown) in an easily reachable position. This second memory 106 stores nine "part" programs for nine different sewing patterns and may be a 2, 4 or 8 Kbyte type, according to the complexity of the patterns.

Leaving out details of logic operation relating to some of the functions connected with the machine cycle, for example the lowering and the raising of the frame and of the presser foot, there will now be provided a detailed description of the control system for control of the fabric clamp position.

Two optical incremental encoders (Fig. 5) are mounted on the shafts of the two motors, each of these encoders producing three signals. The first signal, at the frequency of one pulse per revolution, has the task of identifying the coordinates 0,0 as will be explained hereinafter. The other two signals, in sinusoidal form, are generated by two series of 200 notches formed in, respectively, two concentric circumferences of the discs of the two encoders. Through elaboration of these signals, 400 pulses per revolution are obtained, which, depending on the selected drive ratio, permit a resolution of 0.015 millimetres.

These signals, phase-shifted early or late by 900 according to the direction of rotation of the motor, are supplied to a component 108 (Fig. 4) of a logic circuit, where they are converted to square wave signals with unvaried phase in order to be compatible with logic circuits formed exclusively by components of the TTL family. The elements of the two circuit parts respective to the axes X and Y are designated in Fig. 4 by the same reference numbers.

The component 108 also has the task of generating an output voltage at an output 110, which is used as a reference voltage for closing a speed feedback loop.

As a function of the encoder signals, an output voltage is also generated at an output pin 11 6, this voltage being proportional in amplitude and direction to the motor speed.

From the outputs 112 and 114 of the component 1 08, the two square wave signals are fed to a portion of the logic circuit in which a position loop is closed, as it will be hereinafter explained.

In order to obtain short positioning times, a speed loop and a current loop are provided inside and concentrically with the position loop. The speed loop is closed as follows: At the output 11 6 of the element 108, as already mentioned, a voltage signal is supplied which is a function of the motor speed. This signal, filtered by an R-C group (not shown) after having been converted to a current signal, is delivered to an input 118 of an element 120 formed by a 6 bit D/A converter and an error amplifier. A speed error or difference is obtained by a comparision between the signal at input 11 8, namely a signal indicating instantaneous speed, and a signal indicating required speed after conversion from digital to analog form.The signal indicating required speed is obtained in the microprocessor 100 in the following manner: The microprocessor reads in the EPROM 106 the data relative to a position which must be attained during the execution of a pattern and also reads from an integrated counter 1 22 the instantaneous position of the fabric clamp driven by the two motors. This instantaneous position is defined by the square wave signals derived from the encoder pulses by the element 108, these signals being supplied to the counter 1 22 through the logic circuit. The operation of the logic circuit and of the counter will be explained in more detail subsequently.For the moment it is sufficient to say that the counter 1 22 detects the instantaneous position through four separate internal counters, two for counting up and two for counting down, for the two axes.

These counters are periodically read and interpreted by the microprocessor.

The operative position of each motor is obtained by addition of all the pulses produced by forward rotation of the respective encoder and subtracting therefrom the total of all the pulses produced by rotation of that encoder in the opposite direction.

The error or difference between the digital signal corresponding to the required position, stored in the EPROM 106, and the digital signal corresponding to the instantaneous position supplied by the counter 122, is amplified by a certain constant in the microprocessor 100. This results in generation of a particular speed command to effect cancellation of the error (required speed command). This speed command, appearing at the output of the microprocessor, is fed to an input of the D/A converter of the element 120. The D/A converter provides as an output a current signal proportional to the speed code at its input, which in turn is proportional to the position error.

At this point, in the element 120 the two currents are compared by the error amplifier, namely the current corresponding to the required speed, supplied by the D/A converter with the contribution of the reference voltage from the output 110 of the element 108, and the actual current corresponding to the actual speed, from the output 11 6 of the element 108. The resulting signal, converted to voltage by an appropriate resistor, is supplied to a unit 124 for generation of a command current for a power amplifier feeding the respective D.C. motor, with the task of regulating the strength of said command current.

This signal has the purpose of shifting the level of the middle value of the triangular wave generated by the circuit, so that it intersects two thresholds of fixed voltage at points which are continuously different and depend on the current error. The intersection at different points of a triangular wave means that square waves are obtained which have a constant frequency but with a fullempty ratio which varies with this frequency.

These square waves will be used for controlling the above-mentioned power amplifier with average duration variable as a function of the current error.

In known manner, from the five secondary circuits of a transformer, having its primary circuit connecting to an electric power source, five voltages of different values are supplied for energizing the various parts of the control system, namely a 5V voltage for the logic circuit, two voltages of + 1 2V and -1 2V for the analog circuit, the three voltages being rectified, filtered and stabilized in a usual manner, a rectified and filtered voltage of +24V for the inputs and outputs, which are afterward opto-isolated, and a 35V voltage for feeding the D.C. motors.

With reference to Fig. 5, the feed circuit for the motors positioning the fabric clamp 30 utilises a minimum number of transistors (eight) and in this manner is able to command 1 OA currents without further intermediate amplification stages. The voltages, supplied by the unit 124 through the output resistors in form of square waves, which repeat with fixed frequency of 20Hz but vary in duty-cycle, enter one transistor couple 1 30 and 132 and another transistor couple 134 and 138.

These transistors have the purpose of controlling the two diagonals of an H bridge in the middle of which one of the motors, for example motor 58, is connected.

Two shunt resistors 140 and 142 enable a voltage signal proportional to the current flowing in the motor to be derived and the current loop to be closed. By way of explanation of the control operation of the transistors feeding the motor, when the signal on a feed lead 144 is high, it saturates the transistor 1 30 and blocks the transistor 1 32. The saturation of the transistor 130 permits, on one hand, the current to flow through a resistor 146 so as to close a transistor 148 and to close a transistor 1 50. This diagonal is thus closed and the current can flow from right to ieft, energizing the motor. When the signal on the lead 1 44 is low, it completely blocks all the circuitry. The same applies to the signals on a further lead 1 60 for operating the other diagonal, comprising transistors 1 52 and 1 54.

The dephased signals from the two encoders, after appropriate elaboration, are sent from the outputs 112 and 114 of the element 108 to a part of the loop provided for each axis by the counter 122, three inverters 111,113 and 115 and two multiplexers 117 and 119. Referring to the axis X, the signals from the outputs 112 and 114 of the element 108 and denominated A and B are fed to the input of the multiplexers 117 and 11 9 as selection signals. The signal A is also shunted and fed into the two first inverters 111 and 113.It is then fed in parallel through a first branch, connected to the input of the first multiplexer 11 7 directly, with the new reference letter A1, and through a second branch, connected to the multiplexer 11 7 by way of a third inverter 11 5, with the reference letter A1. The other two inputs of the multiplexer 11 7 are connected to earth. The two multiplexers 11 7 and 119 for each axis respectively register the "up" pulses and the "down" pulses.

The signals A1, A, entering the first multiplexer 11 7 are shunted to two inputs of the second multiplexer 119. The two remaining inputs of the multiplexer 119 are connected to earth.

According to the combinations of the two selection signals A, B, namely 00, 01, 10, 11, the signal present at the input selected by one of the four combinations is qualified at the outputs of the multiplexers. Since the signals A, and A, at the inputs are phased shifted slightly late with respect to the selection signal A, at the output of the multiplexers there will be up and down signals as represented in Fig. 6, where the references D and U indicate, respectively, the down signals and the up signals.

A feature of this control system is that when vibrations act on the motor at rest with the result that a notch of the first series of notches in the encoder discs is constantly in shadow while a notch of the other series is alternatively in shadow and light, there are alternatively up and down signals supplied to both counters so that the algebraic sum of the content of the two counters remains constant.

The EPROM 106 is inserted in the command panel of the sewing machine so that it can be replaced as desired by the operator. Three types of EPROM are provided with 2K, 4K and 8K bytes and the microprocessor can be adapted to recognise which of the three types is connected to the control system.

For this purpose, in the last cell of each memory a recognition code is previously stored.

At the beginning of a program, the microprocessor addresses this cell, sending the code 1 on all thirteen available bits.

The three types of EPROM differ as specified below: 2K=1 1 bits address=one input fixed at 1.

4K=12 bits address=previous input used as address input.

8K=13 bits address=input used as in the type 4K.

If the microprocessor reads the code of an EPROM 2K, it keeps one input fixed at 1 and uses only 11 address bits comprising thus the input fixed at 1 in the 2K. If the microprocessor reads the code of an 8K, it uses 1 3 address bits, thus comprising the supplementary input which, in the case of the 2K and 4K, is not connected to the EPROM memories, being these elements not provided with a connection in correspondence with the thirteenth input.

The above-described electronic control device includes a safety device for returning the fabric clamp to a start position with the coordinates 0,0 at the beginning of a pattern sewing cycle. This is based on simultaneous occurrence of two events, namely passage of a zero notch of the encoders in front of the corresponding light sources and the operation of the microswitches 88 by the two followers 86 (Fig. 1). Each of the microswitches 88 is connected, as shown in Fig. 4, to a respective inverter 4 and each inverter 4 is connected at its output to one of two inputs of a NAND gate 6, the other input of the gate 6 being connected to an output of the element 108 at which a square wave signal 0 derived from the respective encoder is present. Only when contemporaneity of two signals 1 at the inputs of the two NAND gates 6 is verified is a signal 0 supplied to the microprocessor 100 to initiate stopping of the two motors.

Claims (5)

Claims

1. A sewing machine provided with pattern control means to enable automatic sewing of patterns by the machine, the pattern control means comprising fabric retaining means displaceable in a work plane in any direction relative to sewing means of the machine by displacing means, and an electronic control device to control operation of the displacing means in dependence on a signal feedback therefrom, the control device comprising loop means including incremental encoder transducer means for providing signal pulses in dependence on displacement of the displacing means, logic circuit means to combine the pulses to provide signals indicative of the operation of the displacing means, counting means to determine the instantaneous position of the retaining means from such signals, and a microprocessor interfaced with the counting means for comparison of the determined instantaneous position with a required position to enable corresponding control of the displacing means by way of the logic circuit means, the loop means comprising a position loop for the position of the retaining means and a displacement speed loop and a current loop both concentric with the position loop.

2. A sewing machine as claimed in claim 1, the logic circuit means comprising signal multiplexing means arranged to process the signal pulses from inverting and non-inverting feeds in such a manner as to provide signals indicative of displacement of the retaining means in orthogonal directions.

3. A sewing machine as claimed in either claim 1 or claim 2, wherein the control system further comprises a plurality of selectively accessible EPROM storage units associated with the microprocessor and each for storage of data relating to co-ordinates of stitch positions in a respective sewing pattern, the microprocessor comprising recognition means for recognition of a storage unit selected for access.

4. A sewing machine as claimed in any one of the preceding claims, wherein the control system is adapted to so control the displacing means as to cause the retaining means to be disposed in a central position with respect to a range of displacement thereof at the commencement of a sewing cycle by the machine.

5. A sewing machine provided with pattern control means substantially as hereinbefore described with reference to the accompanying drawings.