Device for supplying upper thread of sewing machine

Sewing – Elements – Thread guiding or handling

Utility Patent

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Utility Patent

active

06167826

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an upper thread supply device having a drive roller driven by a drive motor and a slave roller disposed in contact with the drive roller. The drive roller and the slave roller hold a thread there-between and feed the thread by rotation of the drive roller.
2. Description of the Related Art
Japanese Utility-Model-Application Publication (Kokai) No. HEI-1-111581 discloses an upper thread supply device with a drive roller and two slave rollers that all extend parallel to each other. The slave rollers are disposed adjacent to the drive roller. Drive force from a motor is transmitted to the drive roller by gears. A thread is sandwiched between the drive roller and the slave rollers, and fed out by rotation of the drive roller.
FIG. 1
shows another conventional upper thread supply device. The device includes a drive roller
158
fixed to the drive shaft of a drive motor
148
, and two slave rollers
170
,
170
. The two slave rollers
170
,
170
have the same shape and are formed from the same material, that is, a thermoplastic rubber. One is disposed upstream, and the other is disposed downstream, with respect to a thread-feed direction. The drive roller is made entirely of non-quench-hardened iron. The slave rollers
170
,
170
are prevented from falling off support members
158
by stopper rings
159
. A thread held between the drive roller
158
and slave rollers
170
,
170
is transported by rotation of the drive roller
158
.
The surface of the drive roller has a low friction coefficient. When oil or dust cling to the outer surface of the drive roller, the thread can slip so that the upper thread cannot be properly fed out. Also, the slave rollers have low friction with respect to the upper thread, so they cannot suitably hold the upper thread when the rollers are stopped. This can result in excessive upper thread being drawn out from the thread spool, resulting in tangling of the upper thread, or in defective stitches. Therefore, a separate electrical magnetic solenoid is provided in order to properly hold the upper thread when the rollers have stopped.
To improve the above-described configuration, a quench hardened metal has been used as the thread contacting portion of the drive roller and a hard resin has been used as the thread contacting portion of the two slave rollers. Using this configuration improves the ability of the rollers to properly hold the thread when the rollers are in a stopped condition.
SUMMARY OF THE INVENTION
However, the upper thread is not stably feed out when both of the slave rollers have the same configuration. Improper thread feed has an adverse effect on stitches.
Also, when a quench-hardened metal is used for the drive roller, the resin slave rollers are quickly worn down to a smooth surface and are not very durable. That is, because the resin thread contacting portions of slave rollers are quickly worn down to a low friction coefficient, they are incapable of stably feeding out the upper thread. As a result of the unstable thread feed, the upper thread can slip and carve into the resin thread contacting portion of the slave rollers. Grooves and scratches formed in the thread contacting portions causes the upper thread to break or cause improper holding of the upper thread. When the upper thread slips, tangling thread can result.
It is an object of the present invention to overcome the above-described problems and provide an upper thread supply device capable of performing proper thread holding and proper thread feed.
In order to achieve the above-described objective, an upper thread supply device according to one aspect of the present invention includes a drive roller driven to rotate by a drive source; a first slave roller disposed in a contact with the drive roller; and a second slave roller disposed in a contact with the drive roller, wherein hardness of the first slave roller and hardness of the second slave roller are different from each other.
With this configuration, the thread is fed by cooperative operation between the drive roller and two slave rollers with different hardnesses. The harder slave roller serves to prevent excessive thread from being drawn from the spool by operation of the thread take up lever, for example. The softer slave roller serves to proper feed the thread. Therefore, the two different roles are properly performed and the thread can be accurately fed.
According to another aspect of the present invention, a drive roller and a slave roller in contact with the drive roller have different hardnesses. This is achieved by using a quench-hardened metal for the thread contacting portion of one and a non-quench-hardened metal for the other. Because both are formed from metal, they can properly hold the upper thread when the rollers are not rotating. Because one is softer than the other, the thread can be accurately fed.
Alternatively, the drive roller and the slave roller can have different hardnesses by providing one with a thread contacting portion formed from a quench-hardened metal and the other with a thread contacting portion formed from a resilient material. With this configuration, the thread can be properly fed.


REFERENCES:
patent: 3982490 (1976-09-01), Bury
patent: 5022335 (1991-06-01), Hanyu et al.
patent: 5042405 (1991-08-01), Bradley et al.
patent: 5467724 (1995-11-01), Bardsley et al.
patent: 419814 (1965-03-01), None
patent: 1-111581 U (1989-07-01), None

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