Sheet stretching device

A sheet stretching device comprising:

• a frame;
• a sheet;
• a first retaining groove and a second retaining groove formed on a front surface side of the frame, the first retaining groove defined by an inner wall and an outer wall spaced apart by a width of the first retaining groove, the second retaining groove defined by an inner wall and an outer wall spaced apart by a width of the second retaining groove, and in each of the first retaining groove and the second retaining groove, an inner surface of the inner wall faces an inner surface of the outer wall across the width of the corresponding one of the first and second retaining grooves;
• and
• a first retaining plate fit into the first retaining groove and a second retaining plate fit into the second retaining groove, the first and second retaining plates being parallel to each other and fitted into parts of the first and second retaining grooves that are spaced apart and parallel to each other, each of the first and second retaining plates formed of an elastic material and having a rectangular cross section with a first side surface attached to a peripheral edge portion of the sheet, a second side surface opposite to the first side surface, and a thickness substantially equal to the width of the corresponding one of the first and second retaining grooves, wherein
• in each of the first and second retaining grooves, the first side surface of a respective one of the first and second retaining plates faces the inner surface of a respective one of the outer walls with the sheet disposed therebetween and the second side surface of the respective one of the first and second retaining plates contacts the inner surface of a respective one of the inner walls,
• the second side surface of one of the first and second retaining plates includes a plurality of projections formed at certain intervals in a depth direction of the corresponding one of the first and second retaining grooves, the first side surface of the one of the first and second retaining plates not including a projection, and
• in a state in which the first and second retaining plates are positioned to protrude from the parts of the first and second retaining grooves that are spaced apart and parallel to each other, a distance between portions of the retaining plates protruding from the retaining grooves is substantially equal to or less than a distance between the parts of the retaining grooves as a result of the elastic material compressing.