Movable Limit Markers for Viewing Glass of Measuring Instruments

The present invention is concerned with measuring instruments containing analog display means, such as having an indicator move along a graduated scale. More particularly, the invention is concerned with a viewing glass which renders the measurement more visible.

Conventional measuring instruments mostly contain an inorganic glass window, usually plane or slightly curved, of uniform clarity which is mounted in front of the display means. Furthermore, in most industrial measurements there is a need to verify whether or not the measurement is in predetermined tolerances. Thus, it would be convenient to furnish the display means with means to affix a marker which is movable and is capable of being adjusted from outside of the instrument to enable the minimum and maximum limits of the tolerance range to be easily observed.

Some instruments, such as those used for the measurement of lengths achieve this object by using two display needles to be placed to indicate the limits. This approach has problems because of high costs and because the marking needles have to be mounted with great care in the viewing glass in order to accurately remain where they have been placed. Additionally, since the position of marking needles are frictionally moved, such mechanism deteriorates with time.

Therefore it is an object of the present invention to provide a viewing glass, capable of being produced with a minimum of expense, which contains simple means of receiving and retaining one or more limit markers which are easily displaced and easily replaced and which are able to be repetitively utilized without deterioration.

These and other objects will appear more clear from the following description which illustrates the provisions of a viewing glass which contains a groove in which markers may be inserted. The viewing glass consists preferably of an acrylic resin and the markers consist of helical springs or of plastic inserts.

Additional advantages, details and characteristics of the present invention will appear from the following description of an embodiment of this invention.

FIG. 1 is a plan view of the viewing glass of a microcomparator; and

FIG. 2 is a view of the cross-section through the viewing glass along line II--II in FIG. 1.

The measuring instrument 1 of FIG. 1 contains a display means consisting of a graduated scale 2 in front of which an indicator needle 3 moves, the needle being actuated by the measuring means. A viewing glass 4 on top of the scale 2 contains a groove 5 extending parallel to the graduated scale 2. Groove 5 receives displaceable markers 7 of which are inserted therein.

As better seen in FIG. 2, the cross-section of the groove 5 in the viewing glass 4 shows the groove having an open mouth construction with narrowing sides or a first portion 8 which narrow towards the front 9 of the groove. This smaller front opening or first portion serves to hold the marker 7 within the groove. Narrowing sides or first portion 8 widen in the immediate vicinity of the surface 10 of the viewing glass 4 along edges or a second portion 11. Widened edges or second portion 11 permits easy introduction of the marker 7 into the groove 5 and also makes it easy for the operator to handle the marker. In order to displace the marker, the operator merely puts one finger into the opening 9 pressing it against the outer surface of this marker sliding it along the groove. The marker 7 may consist of a plastic insert or, as indicated in FIG. 2, of a helical spring. Preferably the groove is furnished with two displaceable markers, each of which allows observing the minimum and maximum tolerance limits related to a specific measurement. Each marker could be made of plastic of a different color, with a red color being used for the maximum and a green color indicating the minimum.

The viewing glass 4 may be formed of an acrylic resin into which the groove 5 may be cut my milling. It also may be made by molding a transparent synthetic resin.

Variations and modifications can, of course, be made without departing from the spirit and scope of the invention.