US3469418A - Apparatus for the regulation of knitting machines - Google Patents

Description

Sept. 30, 1969 STABELER ETAL 3,469,418

APPARATUS FOR THE REGULATION OF KNITTING MACHINES Filed Dec. 29, 1966 2 Sheets-Sheet 1 Fig.1

Eberhard sf'beler Alfred Dunger INVENTORS Attorney Sept. 30, 1969 E, STABELER ETAL 3,469,418

APPARATUS FOR THE REGULATION OF KNITTING mcmuss Filed Dec. 29, 1966 2 Sheets-Sheet 2v I03 I02 111 #4 TE M5 TER V V Eberhard Sffbelr Alfred Dunger 'INVENTORS Y 5 B M 7 Attorney United States Patent 3,469,418 APPARATUS FOR THE REGULATION OF KNITTING MACHINES Eberhard Stiibeler, Reichenbach, VogtL, and Alfred Dunger, Pausa, Germany, assignors to VEB Gardinen-u. Dekowerke Zwickau, Zwickau, Germany, a corporation of Germany Filed Dec. 29, 1966, Ser. No. 610,720 Int. Cl. D04b 9/00 US. CI. 66-56 3 Claims ABSTRACT OF THE DISCLOSURE A method of controlling the starting and stopping of a knitting machine such as a raschel, flat-bed or circular knitting machine having a drive motor connected to the cam or needle-bank assemblies whereby loose loops are avoided at certain critical speeds, at which such loose loops commonly occur, between zero speed and maximum speed by continuously accelerating or decelerating the knitter drive at a constant rate to maintain a tension on the threads or yarns preventing the development of lost loops, slack or the like. The apparatus includes electrical or mechanical acceleration-control means cooperating with a servomechanism for sensing the actual speed of the machine to ensure the constant-rate acceleration or deceleration of the drive.

Our present invention relates to a method of and an apparatus for starting and stopping knitting machines having crank or cam drives and shiftable needle beams or carriages and driven, generally, by an electric motor connected with a rotary input shaft of the machine.

A common problem in the field of machine knitting is the occurrence of loose loops along a course or wale, which are common and tend to develop apparently because of inherent vibrational characteristics arising when the machine operates at less than full speed. The loose chains of loops render the knit fabric unsatisfactory and fabrics containing same are considered to be of poor and nonuniform quality. Investigation into this phenomenon has shown that loose chains or rows of loops result from a temporary detensioning of the yarn or thread supplied to the knitting needles as a consequence of resonant or natural vibration phenomena in the machine. Attempts have been made to avoid these disadvantages by tensioning the individual thread or yarn with special thread-guide devices and the like although such systems have the disadvantage that they act nonuniformly upon the thread and, therefore, are incapable of preventing the phenomena unless extremely high tensile forces are applied. Such tensile forces have the further disadvantage that thread breakage occurs at a high rate.

It is, therefore, the principal object of the present invention to provide a method of and a system for the starting and stopping of circular or flat bed, Raschel, stocking and other knitting looms whereby the aforementioned disadvantages can be avoided and the quality of the knit fabric increased significantly. A further object of this invention is to provide a method of and an apparatus for eliminating the sensitivity of the knitting operation to resonant and natural vibration phenomena during starting and stopping of the machine.

We have now found that these objects can be obtained and loose loops prevented during starting and stopping of the machine by a method which involves the acceleration or deceleration of the input drive shaft at a substantially constant rate to ensure continuous tensioning of all the threads as supplied to all the needles during the full range of speed in which oscillation and vibration of the apparatus tend to develop.

ICC

Practically all knitting loops of the type described are characterized by a range of operating speeds (in terms of the angular velocity of the input shaft) in which the amplitude and frequency of the vibration of the thread-guide element are such as to produce free or loose loops therein. In some cases, this range may extend from zero or low speed to the normal operating speed although, in the more general case, detrimental oscillation and vibration will develop only over a limited portion of this range. Accordingly, we may provide means for accelerating and decelerating the drive shaft of the apparatus at a substantially constant range only during the limited portion of the speed range in which such constant acceleration and deceleration is essential. As will become apparent hereinafter, practically any conventional servomechanism can be used for accelerating and decelerating the knitting machines although we prefer to provide means for sensing the speed of the shaft to feedback a control signal to a servomotor or other control element which, in turn, regulates the acceleration rate or speed of the drive shaft.

According to a further feature of our invention, means is provided for shifting, within the characteristic vibration range of speed of the knitting apparatus (e.g., in terms of angular velocity of the input shaft) the minimum-speed and maximum-speed points determining the range in which substantially constant acceleration or deceleration of the drive is carried out.

As suggested earlier, various mechanisms can be employed for the purposes described. For example, we have found that it is most advisable to directly connect a speed indicator (e.g., a pointer or other scale) with the drive shaft of the knitting machine and/ or the output shaft of the motor, this indicating member being adapted to sweep across a speed scale which may be calibrated in knitting units or shaft revolutions per minute (r.p.m.) or other units of angular velocity. Along this speed scale, We provide a pair of limit switches which may be moved therealong to establish the minimum-speed and maximum-speed points and which together control a servomotor or other mechanism assuring constant acceleration or deceleration of the main motor of the knitting machine. It is convenient, for example, to provide a slip ring-armature motor which is energized by an adjustable input resistance variable by a servomotor controlled by a limit-switch mechanism of the type described. In other machines, a stepless transmission can be employed, the servomotor being then used to shift the actuating member of the stepless transmission. Any other conventional feed adjustment, controlled by an operating member which may be coupled with a servomotor, including commutators, motors, direct current drive and solid-state or rectifying and electronic-switch controls, may be employed.

According to another feature of this invention, the circuit is provided, in addition to the servomechanism for constant-rate acceleration and deceleration of the drive, with an instantaneous-operating cutoff switch for emergency shutdown of the apparatus in the case of thread breakage or other disruption of the mechanism.

The above and other objects, features and advantages of the present invention will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

FIG. 1 is a block diagram representing the system of the present invention;

FIG. 2 is a somewhat more detailed diagram showing some structure which is illustrated only in block form in FIG. 1; and

FIG. 3 is a view similar to FIG. 2 of a portion of the apparatus, partly in block form.

In FIG. 1 we show a block diagram illustrating the principles of the invention in Which a knitting machine KM is driven by a drive motor 3 and is controlled by a speed control 1 whose servo is represented at 6. The speed-control mechanism 1, which is adjustable to accelerate the drive motor 3 or to decelerate the latter within a predetermined range may be a stepless drive or a transmission (e.g. hydraulic or hydrostatic as illustrated in FIG. 3), a commutator motor, a series resistance for a slip ring-armature motor (FIG. 2), a field-coil shifter for a Ward-Leonard set, or a magnetic amplifier or saturable reactor for a transducer switch arrangement of conventional speed-adjusting type.

The basic circuit also includes an instantaneous-stop switch 2 of the pushbutton, rodor lever-actuated type capable of breaking the circuit between the drive motor 3 and the source. The instantaneous-stop switch 2 is actuated upon needle or thread breakage or any other emergency requiring substantially immediate termination of machine operation.

The servomotor 6, which controls the speed-changing means 1, is responsive to the velocity of the knitting machine KM as represented by the feedback network 9. Furthermore, the servomotor 6 is bypassed or rendered ineffective by a pair of limit switches 4 and 5 defining the lower and upper limits of the acceleration range and the deceleration range, respectively. A starting switch 7 and a stop switch 8, respectively, are connected in circuit with the servocontrol 6 and its cutouts 4 and 5.

By way of example, reference is made to the production of an article by a conventional knitting machine with a machine feed assembly of 500 mesh rows or causes per minute. Experience shows that this machine produces defective wales or courses at speeds of 180 to 500 mesh rows per minute, the defective loops being generally loose and extending from the fabric. The switches 4 and 5 are, as indicated earlier, tripped at the lower or minimum-speed point (180 rows per minute) and the upper or maximum-speed point (500 rows per minute) of the range at which defective loops are formed. The switches 4 and 5 may thus be set along a scale at these limits.

When the machine is started by actuation of the switching device 7, the servo 6 is bypassed and the motor 3 energized via switch 7 and limit switch 4 as if no speed control was provided. The machine is thus rapidly brought to a speed of 180 knit rows per minute. At this point, switch 4 is triggered by the speed indicator and the servomotor 6 is energized to drive the speed-control unit 1 and accelerae the output shaft of motor 3 at a constant rate to the speed of 500 knit rows per minute, when the switch 5 is tripped and the machine speed retained at this level. It has been found to be important to carry out the acceleration within this range over a period of 10 to 25 seconds.

Upon operation of the stop switch 8, the servomotor 6 decelerates the motor 3 via the speed-control mechanism 1 at a constant rate from a speed of 500 knit rows per minute to 180 knit rows per minute. At this point, the indicator trips switch 4, and servomotor 6 and the motor 3 are shut down, with the machine holding when its inertia no longer suffices to rotate the shaft. Switch 2 may be tripped automatically or manually to terminate machine operation when a dangerous or damaging condition develops.

In FIG. 2, we show a system generally similar to that represented by the block diagram of FIG. 1. In this system, a source 110 of alternating current energizes the drive motor 103 via an emergency instantaneous cutoff switch represented at 102. The drive motor 103 which may be of the slip ring-armature type, has an output shaft 111 connecting it to the knitting machine KM. The speedresponsive means includes a minimum-speed limit switch 104 and a maximum-speed limit switch 105, these switches performing the functions ascribed to controls 4 and 5 in FIG. 1. To this end, an indicator pointer 112 is carried by a sector gear 113 in mesh with a worm 114 coupled via a chain drive 115 with the rate meter of the shaft 111. The indicator 112 thus can sweep along a scale 116, calibrated in mesh rows per minute or some other representation of the knitting machine speed. The limit switches 104 and 105 may be shifted along the scale 116 as represented by the arrows 117 and 118, respectively, thumb screws 119 and 120 being provided to lock the limit switches 104 and 105 adjustably along the scale 116. In this manner, it is possible to accelerate or decelerate the shaft 111 at a constant rate between the range of, say, 0 to 500 rows per minute, although an acceleration/ deceleration range of to 500 is preferred in the example given. The switches 104 and 105 are connected in circuit, respectively, with a start switch 107 and a stop switch 108 which performs functions akin to those described with respect to the starting and stopping controls 7 and 8. The switches 107 and 108 effectively shunt the servocontrol 106 which may be provided with a feedback 109 from a governor connected with the shaft 111 or any other speed-control device. To this end, a tachometer or other rate-measuring instrument may form the feedback control (cf. pages 320 ff, Servomechanism Practice, Ahrendt and Savant, McGraw-Hill Publishing Company, second edition, 1960). The servomotor 106 can shift the control member 101 of a potentiometer or variable resistor 121 connected in series with the motor 103. The system of FIG. 2, of course, operates in the manner previously described.

In FIG. 3 we show a modified system wherein the motor 203 is a constant-speed motor but is coupled with the knitting machine KM via a stepless variable-speed transmission 201 of the hydraulic type. In fact, any continuously adjustable transmission may be provided. In this case, the servomotor 206 is connected with the actuating arm 201' of the variable-speed drive. The feedback 209 can thus include an accelerometer 209 in addition to the indicator 112, the switches 104 and 105 and the starting and stopping controls 107 and 108 as previously described. The acceleration-type feedback may be of any conventional type, cf. pages 333 ff. of Servomechanism Practices (op. cit.).

The invention described and illustrated is believed to admit of many modifications within the ability of persons skilled in the art, all such modifications being considered within the spirit and scope of the appended claims.

We claim:

1. A knitting apparatus comprising, in combination:

a knitting machine having a bank of knitting needles for forming interengaged thread loops and an input shaft for operating said needles;

a drive motor energizable for rotating said shaft whereby said machine has a normal operating speed and a limited characteristic speed range of said shaft Within the range from zero speed to said normal operating speed at which loose loops develop in the knit fabric; and

control means connected with said motor for operating said shaft with a constant rate of change of the speed of the shaft with time within said characteristic speed range, said control means including:

a speed-adjusting mechanism connected with said drive motor and having a control member;

a servomotor coupled with said member for displacing same;

feedback means across said servomotor for automatically adjusting the same to maintain the rate of change of the speed of said shaft constant within said characteristic speed range;

a speed indicator responsive to the speed of said machine and said shaft; and

limit-switch means operable by said indicator for selectively controlling said servomotor for the operation thereof within said characteristic speed range, said limit switch means including a pair of limit switches for respectively energizing said servomotor upon attainment of the minimum speed of said range and deenergizing said servomotor upon attainment of the maximum speed of said range, and means for adjusting the positions of each of said limit switches relative to one another and to said indicator.

2. The combination defined in claim 1 wherein said speed indicator sweeps along a scale, said limit-switch means further comprising means for adjustably setting at least one of said limit switches along said scale to control selectively the corresponding limit of the characteristic speed range to which said servomotor responds.

3. The combination defined in claim 2 wherein said speed-adjusting mechanism is a resistor connected in series with said drive motor and said member is a wiper of said resistor.

References Cited UNITED STATES PATENTS FOREIGN PATENTS France. Germany. Germany. Great Britain. Great Britain.

OTHER REFERENCES The Textile Manufacturer, October 1966, pp. 405-407.

WM. CARTER REYNOLDS, Primary Examiner US. Cl. X.L.

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