Inner diameter measuring device

1. An inner diameter measuring device for measuring an inner diameter of a hollow object to be measured, wherein said inner diameter measuring device comprises a circulation unit and a measuring head and is insertable into inside of an object to be measured, wherein said measuring head has a contact measuring unit for measuring the inner diameter by contacting an inner surface of the object to be measured and an advancing/retreating unit for making said contact measuring unit to advance and to retreat in a radial direction and a scale unit, and wherein said circulation unit can rotate said measuring head around a center line of said inner diameter measuring device,

wherein said advancing/retreating unit has a measuring unit holder which holds said contact measuring unit and is able to move integrally with said contact measuring unit in radial direction and wherein said scale unit comprises a scale sensor movable integrally with said measuring unit holder and a linear scale provided in parallel to moving direction of said contact measuring unit, wherein a measurement of the inner diameter is determined based on an amount of moving of said measuring unit holder in radial direction as detected by said scale sensor and on a detection result of said contact measuring unit.

2. An inner diameter measuring device according to claim 1 , wherein said circulation unit is provided at a front end of a rod-like supporting member.

3. An inner diameter measuring device according to claim 1 , wherein a center of gravity of said measuring head is at a position on said center line or approximately at a position on said center line.

4. An inner diameter measuring device according to claim 1 , wherein said measuring head has a measuring unit supporting base plate to be circulated by said circulation unit, said advancing/retreating unit is provided on said measuring unit supporting base plate via two sets of linear guides, wherein each of the linear guides comprises a pair of advancing/retreating guide rails and a pair of blocks slidably fitted to said advancing/retreating guide rails, wherein with respect to one of said linear guides, said advancing/retreating guide rail is provided on said measuring unit supporting base plate, and said block is provided on said advancing/retreating unit, and with respect to the other of the linear guides, said advancing/retreating guide rail is provided on said advancing/retreating unit and said block is provided on said measuring unit supporting base plate.

5. An inner diameter measuring device for measuring an inner diameter of a hollow object to be measured, wherein said inner diameter measuring device comprises a circulation unit and a measuring head and is insertable into inside of an object to be measured, wherein said measuring head has a contact measuring unit for measuring the inner diameter by contacting an inner surface of the object to be measured and an advancing/retreating unit for making said contact measuring unit to advance and to retreat in a radial direction, and wherein said circulation unit can rotate said measuring head around a center line of said inner diameter measuring device, wherein said measuring head has a measuring unit supporting base plate to be circulated by said circulation unit, said advancing/retreating unit is provided on said measuring unit supporting base plate via two sets of linear guides, wherein each of the linear guides comprises a pair of advancing/retreating guide rails and a pair of blocks slidably fitted to said advancing/retreating guide rails, wherein with respect to one of said linear guides, said advancing/retreating guide rail is provided on said measuring unit supporting base plate, and said block is provided on said advancing/retreating unit, and with respect to the other of the linear guides, said advancing/retreating guide rail is provided on said advancing/retreating unit and said block is provided on said measuring unit supporting base plate.