Extendable arm
An extendable arm includes first and second rigid members forming a cross unit. Each rigid member includes one end portion including one of end coupling shafts, the other end portion including the other end coupling shaft, and a middle portion including a middle coupling shaft. The one end portion of each rigid member includes a bottom-side outer side surface that surface-contacts a base surface when the extendable arm in an extended state is placed thereon. The other end portion of each rigid member includes a top-side outer side surface extending parallel to the bottom-side outer side surface of each rigid member. The middle portion of each rigid member includes a middle strip region passing through a middle coupling shaft and perpendicular to the bottom-side outer side surface and the top-side outer side surface.
1. An extendable arm that is comprised of a plurality of cross units arranged in one direction and pivotally coupled to each other, each of the cross units being comprised of first and second rigid members crossing each other in an X shape and pivotally coupled at their intersection via a middle coupling shaft, and adjacent ones of the cross units being pivotally coupled at their ends via upper and lower end coupling shafts, wherein
each of the rigid members includes one end portion including one of the end coupling shafts, the other end portion including the other end coupling shaft, and a middle portion including the middle coupling shaft,
the one end portion of the first rigid member includes a bottom-side outer side surface that surface-contacts a base surface when the extendable arm in an extended state is placed thereon,
the other end portion of the first rigid member includes a top-side outer side surface extending parallel to the bottom-side outer side surface of the first rigid member,
the middle portion of the first rigid member includes a middle strip region passing through the middle coupling shaft and perpendicular to the bottom-side outer side surface and the top-side outer side surface of the first rigid member,
the other end portion of the second rigid member includes a bottom-side outer side surface that surface-contacts the base surface when the extendable arm in the extended state is placed thereon,
the one end portion of the second rigid member includes a top-side outer side surface extending parallel to the bottom-side outer side surface of the second rigid member, and
the middle portion of the second rigid member includes a middle strip region passing through the middle coupling shaft and perpendicular to the bottom-side outer side surface and the top-side outer side surface of the second rigid member.
2. The extendable arm according to claim 1 , wherein
each of the rigid members is shaped so that an imaginary line connecting the end coupling shafts and the middle coupling shaft extends straight.
3. The extendable arm according to claim 1 , wherein
each of the rigid members is shaped so that an imaginary line connecting the end coupling shafts and the middle coupling shaft is curved in an arc shape.
4. The extendable arm according to claim 1 , wherein
the one end portion, the middle portion, and the other end portion of each of the rigid members have a strip shape, and
the strip-shaped one end portion and the strip-shaped middle portion meet at right angles, and the strip-shaped middle portion and the strip-shaped other end portion meet at right angles.
5. The extendable arm according to claim 4 , wherein
at least one of the strip-shaped one end portion and the strip-shaped other end portion of each of the rigid members includes a tip-end projecting strip portion extending parallel to the strip-shaped middle portion from a tip end of the at least one of the strip-shaped one end portion and the strip-shaped other end portion.
6. The extendable arm according to claim 5 , wherein
when the extendable arm is in the extended state, a tip end face of the tip-end projecting strip portion abuts on an inner side surface of the rigid member of the adjacent cross unit.
7. The extendable arm according to claim 5 , wherein
both the strip-shaped one end portion and the strip-shaped other end portion of each of the rigid members include the tip-end projecting strip portion, and
when the extendable arm is in the extended state, a tip end face of each of the tip-end projecting strip portions abuts on a tip end face of the tip-end projecting strip portion of the rigid member of the adjacent cross unit.
8. The extendable arm according to claim 1 , wherein
when the extendable arm is in the extended state, an inner side surface of the one end portion of the first rigid member abuts on an inner side surface of the other end portion of the first rigid member of the adjacent cross unit, and
when the extendable arm is in the extended state, an inner side surface of the one end portion of the second rigid member abuts on an inner side surface of the other end portion of the second rigid member of the adjacent cross unit.
9. The extendable arm according to claim 1 , wherein
each of the rigid members has a parallelogram outer shape, and
an outer side surface of each of the rigid members surface-contacts the base surface when the extendable arm in the extended state is placed thereon, and when the extendable arm is in the extended state, a tip end face of the one end portion of each of the rigid members abuts on a rear end face of the other end portion of the rigid member of the adjacent cross unit.
10. The extendable arm according to claim 9 , wherein
a tip end face of the one end portion of each of the rigid members has a first stepped portion with a step shape, and
a tip end face of the other end portion of each of the rigid members has a second stepped portion that mates with the first stepped portion.