Virtual image display device
A virtual image display device includes a light source, an image member, a Fresnel lens array having an array structure of Fresnel lens units. Each of the Fresnel lens units includes divided lens surfaces that commonly curve convexly or concavely. The array structure includes eccentric Fresnel lens units as the Fresnel lens units. The divided lens surfaces have curvature centers offset from an individual center axis line. Each of the eccentric Fresnel lens units has an offset amount defined as a distance of the curvature centers from the individual center axis line. The offset amount of the eccentric Fresnel lens unit having a larger value of the inter-axis distance between the overall reference axis line and the individual center axis line is greater than the offset amount of the eccentric Fresnel lens unit having a smaller value of the inter-axis distance.
1 . A virtual image display device that displays a virtual image by projecting light of an image onto a projection portion, the virtual image display device comprising:
a light source that emits the light;
an image member that forms the image by partially shielding the light; and
a Fresnel lens array arranged in an optical path between the light source and the image member and having an array structure in which a plurality of Fresnel lens units are arrayed, each of the plurality of Fresnel lens units having an individual area, wherein
an overall reference axis line is defined as a virtual center line of the array structure that passes through the array structure,
an individual center axis line is defined as a center line of the individual area that is parallel to the overall reference axis line and passes through the individual area,
each of the plurality of Fresnel lens units includes a plurality of divided lens surfaces, the plurality of divided lens surfaces curving convexly or the plurality of divided lens surfaces curving concavely,
the array structure includes a plurality of eccentric Fresnel lens units as the plurality of Fresnel lens units,
the plurality of divided lens surfaces of each of the plurality of eccentric Fresnel lens units have curvature centers that are offset from the individual center axis line toward a same side of the individual center axis line, the same side being an overall reference axis side of the individual center axis line that is close to the overall reference axis line or an opposite side of the individual center axis line that is away from the overall reference axis line,
the curvature center of each divided lens surface belonging to the same eccentric Fresnel lens unit is offset from the individual center axis line by a specific offset amount that is set every eccentric Fresnel lens unit,
an inter-axis distance is defined as a distance between the overall reference axis line and the individual center axis line,
the specific offset amount of the eccentric Fresnel lens units having a larger value of the inter-axis distance is greater than the specific offset amount of the eccentric Fresnel lens units having a smaller value of the inter-axis distance, and
a composite lens surface including a convex array lens surface and a single convex lens surface, the convex array lens surface including a plurality of small convex lens surfaces arrayed on a curve of the single convex lens surface, a curvature radius of each of the plurality of small convex lens surfaces being smaller than a curvature radius of the single convex lens surface.
2 . The virtual image display device according to claim 1 , wherein
the array structure further includes a single paraxial Fresnel lens unit as one of the plurality of Fresnel lens units,
the individual center axis line of the single paraxial Fresnel lens unit is coaxial with the overall reference axis line, and
the plurality of divided lens surfaces of the single paraxial Fresnel lens unit have curvature centers located on the individual center axis line.
3 . The virtual image display device according to claim 1 , wherein
the light source emits the light from a light source arrangement surface that has a planer shape,
a reference plane is set among the plurality of Fresnel lens units to be parallel to the light source arrangement surface, and
the plurality of divided lens surfaces are arranged along the reference plane.
4 . The virtual image display device according to claim 1 , wherein
the plurality of divided lens surfaces curve convexly, and
the curvature centers of the plurality of divided lens surfaces of each of the plurality of eccentric Fresnel lens units are offset from the individual center axis line toward the opposite side of the individual center axis line that is away from the overall reference axis line.
5 . The virtual image display device according to claim 1 , wherein
the plurality of divided lens surfaces curve convexly, and
the curvature centers of the plurality of divided lens surfaces of each of the plurality of eccentric Fresnel lens units are offset from the individual center axis line toward the overall reference axis side.
6 . The virtual image display device according to claim 1 , wherein the image member is a panel having a flat plate shape.
7 . The virtual image display device according to claim 1 , wherein the entire composite lens surface is formed by the plurality of Fresnel lens units to form the Fresnel lens array.
8 . The virtual image display device according to claim 1 , wherein each of the plurality of small convex lens surfaces corresponds to each of the plurality of Fresnel lens units of the array structure.
9 . The virtual image display device according to claim 6 , wherein the image member is a transmissive TFT liquid crystal panel using a thin film transistor.
10 . The virtual image display device according to claim 2 , wherein
the single paraxial Fresnel lens unit has a symmetric shape with respect to the individual center axis line as a symmetry axis, and
each of the plurality of eccentric Fresnel lens units has an asymmetric shape with respect to the individual center axis line.
11 . The virtual image display device according to claim 2 , wherein
the curvature center of each divided lens surface belonging to the single paraxial Fresnel lens unit is arranged on the individual center axis line.