Extension-retraction device

An extension-retraction device comprising:

• a tubular structure that is expandable and contractible along a central axis of the tubular structure;
• an inner guide member that is disposed inside the tubular structure, and configured to receive driving force from a drive source and rotate around a central axis of the inner guide member, the inner guide member including a spiral groove formed on an outer peripheral surface of the inner guide member;
• and
• a cylindrical member that has a cylindrical shape so as to conform to the outer peripheral surface of the inner guide member, wherein
• the tubular structure includes
• an inner strip member helically windable around the spiral groove,
• an outer strip member helically windable around an outer circumference of the inner strip member,
• an engaging portion of the inner strip member formed on the inner strip member and including a plurality of holes and a plurality of protrusions that protrude toward a side of the inner guide member, and
• an engaging portion of the outer strip member formed on the outer strip member and including a plurality of protrusions that protrude toward the side of the inner guide member,
• the plurality of the protrusions of the engaging portion of the outer strip member are inserted into the plurality of the holes of the engaging portion of the inner strip member such that the engaging portion of the outer strip member and the engaging portion of the inner strip member engage with each other, in a state where the outer strip member and the inner strip member are helically wound around the inner guide member,
• the plurality of the protrusions of the engaging portion of the inner strip member is fitted into the spiral groove in a state where the inner strip member is helically wound around the inner guide member,
• the cylindrical member includes a friction reducing portion that is configured to contact the outer strip member and the inner strip member such that the friction reducing portion reduces friction generated between an inner periphery of the cylindrical member and the outer strip member, and between the inner periphery of the cylindrical member and the inner strip member,
• the plurality of the protrusions of the engaging portion of the outer strip member include a first protrusion and a second protrusion provided in parallel in a width direction of the outer strip member, the width direction being a short side direction of the outer strip member, and
• the friction reducing portion contacts with the outer strip member at an intermediate position between the first protrusion and the second protrusion.