1. Field of the Invention
This invention relates to an inner diameter measuring instrument for measuring a hole diameter and the like of an article to be measured by measuring elements linearly movable in the radial direction of a spindle, following the movement of the spindle.
2. Description of the Prior Art
As the conventional inner diameter measuring instrument, there has been known one having a construction that a dial gauge is secured to one end of a cylindrical main body, a spindle for pushing and moving a measuring rod of the dial gauge is slidably incorporated in the main body, and measuring elements are provided at the other end of the main body, which are linearly movable in directions perpendicular to the spindle, following the movement of the spindle.
With the conventional inner diameter measuring instrument of the type described, a spring for constantly biasing the measuring elements in the projecting directions is confined between the main body and the spindle, however, in the conventional construction, it has been impossible to adjust the biasing force of this spring from outside. Because of this, when it is desired to change a measuring pressure due to the quality of the material and the like of the article to be measured, the measuring instrument has had to be disassembled to replace the spring with a new one, thus requiring great care, and hence, the need has been voiced for an inner diameter measuring instrument wherein the measuring pressure of the measuring elements is readily adjustable from outside.
Further, in order to retract the measuring elements in measuring the inner diameter of a hole formed in the article to be measured, it has been necessary to cause the spindle to be replaced against the resiliency of the spring, thus requiring the provision of a lever for controlling the spindle from outside.
The conventional inner diameter measuring instrument has been of such an arrangement that the lever comprises a single lever rotatably supported at one end thereof by the main body, a slot is formed at a working end thereof, a pin of the spindle is coupled into the aforesaid slot, and the lever is rotated to directly displace the spindle.
However, since the conventional inner diameter measuring instrument has such a construction that the spindle is displaced against the cylindrical main body by rotation of the single lever, such disadvantages have been presented that, in operating the lever, the posture of the main body becomes unstable, so that the measuring elements abutting against the article to be measured can not be set at positions intended, the lever which is elongated for the purpose of increasing the movement of the spindle causes low controllability, and further, increased frictional resistance between the lever and the pin brings about low controllability in this respect also.
To obviate tho abovc-described disadvantages, there has been proposed such a construction that two levers are provided and these two levers are connected to the spindle by means of a link extending through a slot formed in the cylindrical main body (U.S. Pat. No. 4,288,024 and DE-OS No. 3,001,634).
However, this construcion of connecting by means of the link presents the disadvantages that operation of connecting the link to the spindle is necessitated to be done in a very narrow cylindrical main body, whereby assembling efficiency becomes very low, large-sized components thereof require a large number of man hours for working, and the indispensable provision of the slots in the main body, through which the links are extended, results in low dust exclusion in the main body.