Remote-control system for sewing machine

A remote-control system is used in combination with a sewing machine for controlling revolution of a sewing machine motor. A remote-controller is connected to a main body of the sewing machine and operated by the sewing machine operator to change a resistance value of a variable resistor contained therein so that the sewing machine motor is driven under control in response to an output volume from the variable resistor. A condensor is connected to said variable resistor and chargeable by a power supply source mounted in the sewing machine main body. The output voltage is converted into a corresponding digital value at each timing when the condensor is saturated with electricity in response to a clock pulse signal at a predetermined interval. The output voltage at such timing will be in proportion to the resistance value of the variable resistor which is, in turn, in porportion to the amount of operation of the remote-controller.

BACKGROUND OF THE INVENTION 
This invention relates to a remote-control system for controlling 
revolution of a motor provided for a sewing machine. 
As having been well known in the art, a remote-controller is detachably 
connected to an electronic sewing machine and step-operated by the sewing 
machine operator to control revolution of a motor and therefore to control 
an operating speed of the sewing machine. 
The prior art remote-control system can be classified into two types. One 
is of a two-wire system in which a variable resistor [VR] in a 
remote-controller is connected by a couple of wires to the sewing machine, 
as shown in FIG. 1 (b). An output voltage [Vout] from the variable 
resistor [VR] is determined by the following equation (1): 
##EQU1## 
The r1=0 when no step-operation is applied to the remote-controller and is 
varied in proportion to a stepping amount of the remote-controller. 
Accordingly, the output voltage [Vout] will draw a quadratic curve as 
shown in FIG. 1(a). This means that the output voltage [Vout] will not 
increase in proportion to the stepping amount of the remote-controller, 
resulting in less controllability. 
Due to errors in resistance values of the resistors VR and R1, the output 
voltage [Vout] would be varied within a certain range. More particularly, 
in FIG. 1(a), a curve referred to by [VRmin] shows the output voltage 
[Vout] when the actual resistance values of the resistors VR and R1 
provide the minimum VR to R1 ratio, whereas another curve [VR max] traces 
a value of the output voltage [Vout] in the case of the maximum VR to R1 
ratio. A reference value [Vtyp] of the output voltage [Vout] exists in the 
middle of [VRmax] and [VRmin]. 
Now, provided that the remote-controller is made operative or turned on 
when the operator steps the same to the extent that 12.5% of the output 
volume [Vout] is obtained. Such starting point of the remote-controller 
will be determined in dependence upon the output volume [Vout] but may 
actually be varied in a wide range from [ONmin] to [ONmax]. The operator 
could not exactly know when the sewing machine actually starts to operate 
while stepping the remote-controller by degree. 
The operation of the prior art remote-controller of two-wire system has 
been uncontrollable as above described and therefore not put into 
practice, while having in turn an advantage that the sewing machine can be 
operated with safety. If one of the wires connected to the variable 
resistor VR should be broken down, Vout becomes zero resulting in an 
emergency stop of the sewing machine. 
Another type prior art remote-controller is of three-wire system as shown 
in FIG. 2(a) and (b). With this improved remote-controller, the output 
volume [Vout] is obtained in accordance with the following equation (2): 
##EQU2## 
As the resistance r2 increases from zero in proportion with the stepping 
amount of the controller, the output volume [Vout] increases on the 
straight from zero as apparently shown in the above equation (2) and also 
in FIG. 2(b). Thus, the controller of this type has improved 
controllability. FIG. 2(b) also shows that the controller is turned on in 
response to a substantially constant stepping amount, which is effected at 
12.5% of the output volume [Vout] in the example shown, even when the 
resistors VR and R1 have incorrect resistance values. 
According to this prior art controller having improved controllability and 
responsibility, however, when one (terminal No. 3, for example) of the 
wires connected thereto is broken down, Vout will rapidly increase to an 
extremely high level just the same as Vcc so that the sewing machine will 
be rotated at a tremendous speed. It has therefore been required to 
provide means for detecting disconnection of the wires, as a safety 
device. A single cord containing three wires would be of relatively a 
large diameter, which could not easily be reeled in. 
SUMMARY OF THE INVENTION 
It is therefore an object of this invention to provide a novel 
remote-control system for remote-controlling operation of an electronic 
sewing machine, capable of eliminating defects and disadvantages 
encountered in the prior art systems. 
The principal object of this invention is to provide a remote-control 
system for a sewing machine which is of a two-wire system and yet has 
improved controllability and responsibility equivalent to the three-wire 
system. 
According to an aspect of this invention there is provided a remote-control 
system used in combination with a sewing machine for controlling 
revolution of a sewing machine motor, comprising a remote-controller 
operated by the sewing machine operator to change a resistance value of a 
variable resistor contained therein, the variable resistor being connected 
to a first power supply mounted in a main body of the sewing machine so 
that the sewing machine motor is driven under control in response to an 
output volume from the variable resistor. A secondary voltage supply 
source is connected to said variable resistor in said remote-controller 
and chargeable by said first power source in said main body of the sewing 
machine. The output voltage is processed in response to a clock pulse 
signal at a predetermined interval.

DESCRIPTION OF A PREFERRED EMBODIMENT 
In FIG. 3(a), a remote-control system according to this invention comprises 
a remote-controller connectable to an electronic sewing machine. In the 
remote-controller, a secondary voltage supply source or condensor 1 is 
mounted and connected in parallel to a variable resistance [VR] 2. 
In the sewing machine, a MOS (Metal Oxide Semiconductor) type FET (Field 
Effect Transistor) 3 is operated in response to a clock pulse signal sent 
through a gate 5 to supply power from a primary power supply Vcc to the 
condensor 1 in the remote-controller. The current supplied to the 
condensor 1 is controlled by a resistor [R1] 4 having a resistance value 
considerably smaller than that of the variable resistor [VR]2. The voltage 
[Vout] output from the variable resistor [VR] 2 is converted into a 
digital signal by an analog/digital converter 6 which is operated 
responsive to a timing signal supplied from a signal generator 7 at a 
descending timing of the clock pulse signal. 
In the system having the above arrangement, FET 3 starts to charge the 
condensor 1 with electrocity as from a time t1, as shown in FIG. 3(b). The 
charged voltage [Vc] of the condensor 1 is determined by the following 
equation (3): 
##EQU3## 
Supposed that R1=0 in the equation (3) for convenience's sake, the 
following equation (4) can be obtained: 
##EQU4## 
In this equation (4) t=0 at t1. At a time approximate to t2, as t will have 
a value considerably larger than R1.multidot.C, the following equation 
could nealy be obtained: Vc=Vcc 
FET 3 is turned off at t2. 
The output volume [Vout] at a time t.gtoreq.t2 is represented by: 
##EQU5## 
In this equation t sharts from t2 so that the output volume [Vout] at t2 is 
represented by: 
##EQU6## 
By repeating such operation as shown in FIG. 3(b), the output voltage 
[Vout] can be obtained at t2, t4, t6, . . . which is just proportional to 
the stepping amount of the controller as well represented by the equation 
(7). The output voltage [Vout] is converted into a corresponding digital 
value by the A/D converter 6 responsive to the timing signal each 
generated at t2, t4, t6, . . . . 
FIG. 3(c) shows relation between the output volume [Vout] obtained at t2, 
t4, t6, . . . and the stepping amount. As shown, the stepping amount 
required to make the sewing machine operative, which is established when 
12.5% of the output volume [Vout] is obtained in the embodiment shown, 
will be substantially standstill and not varied regardless of the 
resistance VR to R1 ratios being varied. 
In this embodiment, if one of the wires connected between the sewing 
machine and the remote-controller, the output voltage [Vout] becomes zero 
to stop the sewing machine operation, in the like manner as in the prior 
art two-wire system. 
Although the invention has been described in conjunction with a specific 
embodiment thereof, it is to be understood that many variations and 
modifications may be made without departing from spirit and scope of the 
invention as defined in the appended claims. For example, the output 
voltage [Vout] may be of a maximum value when no operation is applied to 
the remote-controller and decreased in proportion as the stepping amount 
of the remote-controller increases.