Embroidery hoop with an outer contour deviating from the circula

Details Embroidery hoop with an outer contour deviating from the circula Embroidery hoop with an outer contour deviating from the circula

1991-01-29

1993-08-24

Crowder, Clifford D.

Sewing

Special machines

Embroidering

381022, D05C 904

Patent

active

052379418

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention pertains in general to embroidery hoops consisting of a closed inner hoop and a tensioned outer hoop surrounding the inner hoop for holding the fabric to be embroidered.


BACKGROUND OF THE INVENTION

The embroidery frames used for locally clamping fabrics on embroidery heads of embroidery machines consist of a closed inner hoop, and a slotted outer hoop which is connected at its ends by a tensioning device and surrounds the fabric of the inner hoop with an intermediate gap. The hoops are made of the same material, such as wood or plastic. To process embroidery patterns of different geometric size, embroidery hoops with round, elliptical and even nearly rectangle-like outer contours with rounded corners are used.
The tensioning device, arranged on the outer hoop outside the symmetry plane, serves to set the holding force between the inner hoop and the outer hoop and permits adaptation to different fabric thicknesses.
Difficulties due to slippage of the fabric as a consequence of the nonuniform distribution of the contact pressures between the inner hoop and the outer hoop, which depends on the local radius of curvature, often occur in the case of the non-circular embroidery hoops that are very commonly used. For example, contact pressure is concentrated in the areas of small radii of curvature, whereas in other areas the contact pressure may drop to such an extent that sufficient clamping of the fabric to be embroidered is not guaranteed.
To avoid these difficulties, circular embroidery hoops with rectangular cross section of the hoop parts in defined diameter steps are known, in order to thus eliminate the effect of different radii of curvature. However, the use of circular tensioning hoops is not advantageous for certain, e.g., elongated embroidery patterns.


SUMMARY AND OBJECTS OF THE INVENTION

It is an object of the present invention to further improve an embroidery hoop with an essentially rectangular outer contour having rounded corner areas and consisting of a closed inner hoop and a tensioned outer loop surrounding the inner hoop holding the fabric to be embroidered between the two hoops. The improvement is such that practically uniform distribution of the contact pressures is achieved over the entire circumference of the embroidery hoop between the inner hoop and the outer hoop.
This task is accomplished by varying the characteristics of the inner hoop between the lesser axis and the greater axis such that the flexural strength or bending stiffness is essentially constant over the entire circumference of the inner hoop and the extension resistance or stiffness in the areas between the two axis decreases continuously such that it reaches a minimum in the area of the smallest radius of curvature.
As a result of deliberate variation of the local rigidity, the distribution of the contact pressures is highly uniform in the entire clamped area of the embroidery hoop due to reduction of the extension stiffness of the inner hoop in the area of the smallest radius of curvature, while a high bending stiffness and the associated low flexibility in the area of the lesser axis are maintained at the same time.
A particularly advantageous embodiment of the inner frame causing the constant bending stiffness is to have the cross section of the inner frame continuously changed from an essentially rectnagular profile in areas of the largest radii of curvature to an essentially T-shaped profile with a horizontally inwardly directed web reaching its minimum cross sectional area, in the areas of the smallest radii of curvature.
The uniformity of the distribution of the contact pressures is further increased by having the rigidity distribution of the outer frame be opposite that of the inner frame and also having the bending stiffness essentially constant over the entire circumference. The extension resistance between the two axis continuously increases such that it reaches a maximum in the area of the smallest radius of curvature. One particularly advantageous embodiment of the

REFERENCES:
patent: 623301 (1899-04-01), Allen
patent: 4247998 (1981-02-01), Foss
patent: 4422251 (1983-12-01), Hedrick
patent: 4451997 (1984-06-01), Jones
patent: 4642924 (1987-02-01), Sudderth et al.
patent: 4762076 (1988-08-01), Wakaizumi
Mechanical Engineering Design, McGraw-Hill Book Co., 4th Edition, pp. 10-13.

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