ARRANGEMENT OF A HAND WHEEL ON A SEWING MACHINE

Abstract: The invention makes it possible to rotate an arm shaft of a sewing machine without a mechanical clutch between the hard wheel (10) and the arm shaft (23). The position of the hand wheel which previously was very dependent on the mechanical system, can now be chosen so that the best possible ergonometry is obtained. An electrical sensor (16, 17) of the rotation of the hand wheel and another sensor (26, 27) of the movement of the arm shaft are compared in an electronic unit (41), and so long as there is a difference in the outputs of the sensors the electronic unit will cause driving of the sewing machine motor so that the difference will be zero. The movement of the hand wheel is thus repeated on the arm shaft.

Description: The present invention relates to an arrangement of a hand wheel on a sewing machine, preferably an electronic one with control of functional units in the machine by a pulse generator in the driving system, e.g. on the crankshaft. In the past times the hand wheel has always been secured on the upper arm shaft of the machine outside the end surface at the post. By modern machines the hand wheel is very little used, as the motor is brought to drive the machine slowly to desired needle positions or at taking up the bobbin thread. However, it can be necessary by maintenance and checking to rotate the machine shaft slowly to and fro which is simplest made by means of a hand wheel, so it cannot be totally inhibited. From the operator's point of view the wheel can be positioned on, for instance, the front side of the machine which will give it a simpler handling as it then is among the other input and control members of the machine. Another advantage from an ergonomic point of view is that the wheel now controls the machine via the electronic system, not as previously via a mechanical one. It means that the power required on the wheel to rotate the same now can be chosen in such a way that the operator finds the handling of the machine simple. A problem arising by such an optional position of the hand wheel has according to the invention been solved in that the wheel is journalled on its shaft and provided with a code disc rotating in synchronism with the wheel. The code disc is so designed that it forms a two-bit Gray-code. Its pulses are supplied to an electronic unit which in dependence of the direction steps on a counter. The arm shaft of the sewing machine is provided with an equal code disc as that of the hand wheel, and the pulses from the disc are supplied in the same way to the electronic unit and steps on another counter. A similar system with a DC servomotor of a "selsyn" type meaning that a rotation of a first shaft in the system is reproduced on a second shaft, is previously described in a Patent Specification US-A-4,346,334 but such a system is useless in connection with an arrangement of a hand wheel on a sewing machine as described in this application, because it can only reproduce rotation in one direction. However, accordingly to the invention the driving motor of the sewing machine is connected to the unit in such a way that speed and direction on the motor can be controlled by the unit. If someone rotates the hand wheel, its counter will count in dependence of the direction of rotation. This counter is compared to the counter of the arm shaft and, as long as there is a difference between these counters, the electronic unit causes driving of the sewing machine motor so that the difference in the counters will be zero. This means that the arm shaft will always follow the rotation of the hand wheel. The counters are zero-rated when the foot control is actuated and remain zero as long as it is actuated which means that the sewing machine does not react on movements of the hand wheel during periods when the foot control is actuated. A short definition of the invention is given in the characterising part of Claim 1. An embodiment of the invention will now be described in the following with reference to the accompanying drawings which show in Fig. 1 a hand wheel in a plan view, Fig. 2 the same hand wheel in a cross section along the line II - II in Fig. 1, Fig. 3 a portion of the arm shaft with a pulse genarator in a longitudinal section, Fig. 4 a scheme of the principle of the electronic system of the arrangement, Fig. 5 a module in the electronic system. A hand wheel 10 according to Figs. 1 and 2 is journalled on the shaft 12 projecting on a body, panel or the like 11 and has a circular rim 13 protuding on its rear surface consisting of teeth 14 and fissures 15 between them. A pair of opto-sensors 16, 17 are secured on the body straddling above the rim 30 so that a light source 18, 18′ is positioned on one side and a photo transistor 19, 19′on the other. The teeth 14 screen the light and bring about a pulsing light to the transistors, when the wheel rotates. The arrangement of an opto-sensor device at a rim of teeth and fissures is previously described in the Swedish Patent Spec. SE-P 8004226-0. The provision of two opto-sensors 16, 17 is made necessary by the fact that the direction of rotation of the wheel should be indicated. The indication of direction is expressed in the consequence of the electric pulses from the transistor 19, 19′ which have output wires 20, 21 to a decoder 22. The directions of rotation are shown by arrows A and B in Fig. 2. The relation between the A and the output signals as well as the direction B and the other output signals is described in said patent spec. which is herewith referred to. The generic term of binary code in which the bits change character at separate times is Gray-code, and the direction responsive two-bit code obtained on the wires 20, 21 is such a Gray-code. The pulse generator shown in Fig. 3 on an arm shaft 23 has identically equal components, i.e. a code disc 24 with a rim 25 and two opto-sensors 26,27 with output wires 28, 29 to a decoder 30. For the description of the mode of operation of the device it is referred to Fig. 4. From the opto-sensors of the hand wheel and the code disc emanate the wires 20, 21 and 28, 29, respectively, to supply the decoders 22 and 30. The main part is constituted of a s.c. "1 of 16" decoder which in known TTL - technics has a standard circuit number CD 4515B (Fig. 5). The signals are supplied by the opto-sensors on the inputs 31, 32, 33, 34 of which the inputs 32, 34 get the signals via delay circuits 35, 36, so that input codes with respect to phase shift between the transistors are fed simultaneously on the inputs. These ones then receive bits in said Gray -code which is unique and determined by the present direction of rotation. In direction A the decoder supplies pulses on its output 37, and in direction B the pulses are suppled on output 38. From these outputs the pulses pass to binary counters 39, 40 of which the counter 39 counts upwards on rotation according to A and 40 on rotation according to B. Similarly to Fig. 3 the code disc sensor has identically equal components which in Figs. 4 and 5 are marked with ' on the corresponding number. The binary codes from 39, 39′ are fed into a comparator 41 and the codes from 40,40′ into another comparator 42. As soon as the input codes on the comparators are different a signal appears on an output 43, 44, respectively. Thus, a signal on 43 means that the hand wheel rotates in direction A, and a signal on 44 means that it moves in direction B. The signals on 43 and 44, respectively, are passed to a control circuit of the sewing machine motor provided with driving circuit which cause the motor drive forwards or backwards in dependence of the signals from 43, 44. The arm shaft 23 of the machine will then follow the movement of the hand wheel, whatever direction the movement has, and when the comparator senses the same codes on the inputs the signal from the comparator ceases causing a stop of the motor. The shaft has then made the same movement as the hand wheel, despite of the fact that it is mechanically separated from it. The embodiment now described is based on several modules connected to each other, but in practice a microprocessor 46 should be a better solution, since an improvement of the device by introducing a speed control of the motor then is possible, so that also rapid movements of the hand wheel are immediately repeated on the arm shaft. An embodiment with a processor is shown in dashed lines in Fig. 4, where the line 47 represents said speed control.

Claims: 1. Arrangement of a hand wheel on a sewing machine, preferably an electronic one with a driving motor and a motor control circuit which causes driving in dependence of control signals, characterized by pulse generators (16,17) supplying pulses of a two-bits Gray-code indicating angles of rotation of the rotatably journalled hand wheel (10), which pulses are supplied either to a first counter (39) or to a second counter (40) in dependence of the turning direction of the wheel, similar pulse generators (26,27) supplying pulses of a two-bits Gray-code indicating angles of rotation of a shaft (23) in the machine and supplied to a third counter (39′) or a fourth counter (40′) in dependence of the turning direction of said shaft and comparators (41,42) for comparing the numbers of pulses of the counters and a connected supplier of signals of occurring differences between the numbers of pulses from the first and third counters or the second and fourth counters, respectively, transferring said signals to the motor control circuit (45) for driving the motor until the difference has ceased. 2. Arrangement according to claim 1, characterized in that each generator consists of two opto-sensors co-operating with a rotating circular code disc ( 13,25).

Inventors: SKOGWARD, KENNETH OSCAR EMANUEL
Applicants: HUSQVARNA AKTIEBOLAG
Application year: 1987
Main classification: D05B69
IPC codes: D05B69