WO2000005546A2

WO2000005546A2 - Measuring instrument

Info

Publication number: WO2000005546A2
Application number: PCT/US1999/015785
Authority: WO
Inventors: David L. Oberg; James E. Oberg
Original assignee: Oberg David L; Oberg James E
Priority date: 1998-07-21
Filing date: 1999-07-14
Publication date: 2000-02-03
Also published as: WO2000005546A8; WO2000005546A3

Abstract

A measuring instrument (10) is a frame (11) supporting a digital indicator (30). The frame (11) has a base plate (12) having a fixed jaw (14) attached at one end thereof, a top plate (16) having a moveable jaw (18) attached at one end thereof, and a sliding mechanism (20) protected by a dust shield (22) attaching the top plate (16) to the base plate (12) so that the moveable jaw (18) is slidable against the fixed jaw (14). A pair of uprights (24) are attached to either side of the base plate (12) and a crossbar (26) is mounted between the uprights (24) above the top plate (16). The crossbar (26) has a collet (28) securing the digital indicator (30) to the frame (11). The digital indicator (30) has a spring biased plunger (32) or spindle aligned to normally bias the moveable jaw (18) against the fixed jaw (14) and which measures the displacement of the moveable jaw (18) relative to the fixed jaw (14).

Description

MEASURING INSTRUMENT

TECHNICAL FIELD

The present invention relates to measurement apparatus, and particularly to a precision measuring instrument for measuring the length or thickness of a machined object or workpiece, or an injection molded or other finished product, and which may also be used as a depth gauge .

BACKGROUND ART

In the manufacture of goods, various components must be machined, molded or finished to precise specifications in order to ensure a proper fit of the parts. The machinist employs different measurement devices to evaluate compliance of the parts with the required specification. One of the problems with current measuring devices is the problem of repeatability and reproducibility of the measurement. Devices such as micrometers, vernier calipers, comparators, etc. rely on a sense of feel or contact when adjusting the spindle or sliding jaw against the workpiece. Differences in measurement can occur in measuring the length or thickness of an object either between different operators, or between the same operators at different times. Various attempts have been made to improve current devices to alleviate this problem. An improved design for a micrometer is shown in Des . Patent No. 274,990, issued August 7, 1984 to Yamamoto, et al . , and an improved design for a dial gauge is shown in Des. Patent No. 300,009, issued February 28, 1989 to Takahashi, et al . An electronic micrometer with an analog indicator gage and amplifier in a case using a differential transformer detector removably attached to the case is described in U.S. Patent No. 3,768,169, issued October 30, 1973 to Ito. An improved electronic indicator for measuring instruments, including both a digital readout and a circular scale with electrically powered segment pointers to divisions on the circular scale is shown in U.S. Patent No. 4,289,382, issued September 15, 1981 to Earl S. Clark.

Efforts to improve the reproducibility of measurements with micrometers by devices to make the measurements at constant pressures exerted by the spindle on the workpiece are taught by U.S. Patent No. 4,168,575, issued September 25, 1979 to Sugizaki, et al . , including a pair of leaf springs adjusting the pressure of the anvil against the object to be measured according to the hardness of the object by an adjustment screw, and U.S. Patent No. 4,420,887, issued December 20, 1983 to Sakata, et al . , in which the spindle is approximated to the workpiece by a rotary knob connected to the spindle by a pinion shaft and rack, with a coil spring between the knob and the shaft. U.S. Patent No. 4,606,128, issued August 19, 1986 to Wyrwich, et al . , shows a caliper for measuring deformable objects such as brain tumors by using spring biased contact plates and measuring or presetting the pressure at which measurement is made.

U.S. Patent No. 4,485,556, issued December 4, 1984 to Sakata, et al . , and European Patent No. 646,764, published April 5, 1995, describe improvements to micrometers to permit high speed operation. The Sakata patent teaches a micrometer with a spindle rotating in spiral grooves having a large pitch for faster operation. The European Patent teaches a spindle attached to a stopper having a pin extending through a longitudinal slot in an inner sleeve and lodging in a helical groove in an outer sleeve, the helical grooves having a large pitch for high speed operations.

U.S. Patent No. 5,592,747, issued January 14, 1997 to Dennis B. Kessler, shows a Portable Precision Indicator Gage for measuring small objects, preferably 0.18" to 1", with a tubular housing and an indicator device visible through a port in the housing, and an end cap with an anchor pin and a moveable pin, the distance between the pins adjustable by means of an adjustment knob. U.S. Patent No. 5,722,179, issued March 3, 1998 to Adriano Zanier, discloses a method of making a vernier caliper by inserting two longitudinal guide shafts between the slider and the beam in order to reduce the surface contact to produce minimal friction for easier and smoother movement of the slider. None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed. Although these advances, as well as the friction head and the ratchet stop, impart improved functionality to micrometers and vernier calipers, nevertheless, there still remains the problem of reproducibility due to the necessity of manual manipulation to approximate the spindle of the micrometer or the slide of the vernier caliper to the workpiece to be measured. In addition to this problem, in some circumstances the micrometer may impart some degree of torque to the workpiece if the spindle is tightened too much. In order to alleviate these problems, the present invention provides a measuring tool with a moveable jaw actuated by the spring loaded spindle or plunger of a digital indicating device.

DISCLOSURE OF INVENTION

The measuring instrument of the present invention is a frame supporting a digital indicator. The frame has a base plate having a fixed jaw attached at one end thereof, a top plate having a moveable jaw attached at one end thereof, and a sliding mechanism protected by a dust shield attaching the top plate to the bottom plate so that the moveable jaw is slidable against the fixed jaw. A pair of uprights are attached to either side of the base plate and a crossbar is mounted between the uprights above the top plate. The crossbar has a collet securing the digital indicator to the frame. The digital indicator has a spring biased plunger or spindle aligned to normally bias the moveable jaw against the fixed jaw and which measures the displacement of the moveable jaw relative to the fixed jaw. The device is used for measuring the length or thickness of a workpiece by placing the workpiece between the spring biased jaws, or it may be used for measuring depth when aligned vertically with the fixed jaw resting on a horizontal surface and the workpiece resting between the moveable jaw and the indicator.

Accordingly, it is a principal object of the invention to provide a measuring instrument for measuring the length or thickness of a workpiece which provides measurements that are repeatable and reproducible by employing a spring loaded indicator which biases a moveable jaw against a fixed jaw and which measures the displacement of the moveable jaw from the fixed jaw caused by a workpiece placed between the jaws. It is another object of the invention to provide a measuring instrument which may be used either for measuring the length or thickness of a workpiece or for measuring the depth of a hole or cut in a workpiece by altering the vertical orientation of the instrument and the position of the workpiece relative to the moveable jaw.

It is a further object of the invention to reduce human error and improve precision in making measurements of the length or thickness of a workpiece by providing a measuring instrument which approximates the jaws of the instrument to the workpiece without the necessity of making fine adjustments by hand.

It is an object of the invention to provide improved elements and arrangements thereof in an apparatus for the purposes described which is inexpensive, dependable and fully effective in accomplishing its intended purposes .

These and other objects of the present invention will become readily apparent upon further review of the following specification and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is an environmental, lateral view of a measuring instrument according to the present invention shown measuring the thickness of a workpiece .

Fig. 2 is a lateral view with a portion of the dust shield cut away.

Fig. 3 is an environmental, plan view of a measuring instrument according to the present invention shown in use as a depth indicator.

Similar reference characters denote corresponding features consistently throughout the attached drawings . BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is a precision measuring instrument, designated generally as 10 in Figs. 1 through 3. As shown in Fig. 1, the measuring instrument 10 may be used to measure the length or thickness of a workpiece A. The instrument 10 may also be used as a depth indicator for measuring the depth of a hole or an edge cut, as shown in Fig. 3. The measuring instrument includes a frame 11 supporting a digital indicator 30. The frame 11 includes a base plate 12, a fixed jaw 14, a top plate 16, and a moveable jaw 18. The base plate 12 has a substantially rectangular shape and is about 3/4" thick. The fixed jaw 14 is also rectangular in shape, having the same width and about one-half the length of the base plate 12, and is also about 3/4" thick. The fixed jaw 14 is attached to the base plate 12 perpendicularly with one end of the fixed jaw 14 abutting an end of the base plate 12, forming an L- shape or butt joint.

The top plate 16 is also rectangular in shape, having substantially the same dimensions as the base plate 12. A slider 20 mechanism is disposed between the top plate 16 and the base plate 12. The generic slider 20 shown in Fig. 2 includes a top surface 20A attached to the top plate 12, by screws as indicated in broken line, or attached by other suitable means, and a bottom surface 20B attached to the base plate 12 in similar fashion, with a plurality of bearings 20C disposed between the top surface 20A and the bottom surface 20B of the slider 20. A dust shield 22 partially encircles the perimeter of the frame 11 and encloses the slider 20 mechanism to prevent dust and other contaminant particles from entering the slider 20 mechanism and restricting movement of the bearings 20C. The moveable jaw 18 is rectangular in shape, having the same width as the top plate 16, and a length which is shorter than the fixed jaw 14 by about the thickness of the base plate 12. The moveable jaw 18 is abutted perpendicularly to the end of the top plate 16 and secured thereto, by screws as shown in Fig. 2 or by other suitable means, so that the moveable jaw 18 is disposed between the top plate 16 and the fixed jaw 14 and so that the moveable jaw 18 slides into contact with the fixed jaw 14. The length of the moveable jaw 18 is sufficient to permit a portion of the moveable jaw 18 to extend beyond its junction with the top plate 16.

The frame 11 further includes a pair of uprights 24 attached to and disposed upon either side of the base plate 12. A crossbar 26 is disposed between the uprights 24 above the top plate 16. The crossbar 26 supports a collet 28 adapted to receive a suitable digital indicator 30 with a spring loaded plunger 32 or spindle normally biased in an extended position.

The plunger 32 is extended through the collet 28 so that the tip of the plunger 32 contacts the surface of the moveable jaw 18 when the moveable jaw is in contact with the fixed jaw 14 and retracts towards the uprights 24 as the spring compresses by the sliding action of the moveable jaw 18, and the indicator 30 is secured by tightening the collet 28.

The digital indicator 30 has appropriate circuitry for zeroing the display and is continuous in order to measure the distance the plunger 32 is displaced in either direction after the display is zeroed. Preferably, the digital indicator 30 is capable of measuring a displacement of the plunger 32 between zero and four inches . An example of an appropriate indicator 30 and collet 28 combination is a Mitutoyo 543-554A 2" indicator and a Federal AD-87 collet. The force exerted by the spring loaded plunger 32 of the indicator 30 unit against the moveable jaw 18 is normally very small. Hence it is essential that the slider 20 mechanism have a very small coefficient of friction. An example of a suitable slider 20 mechanism is a Techno #H12D83-NBT4125-A, made or distributed by the American division of Techno-isel.

In use, in order to make measurements of length or thickness, the indicator 30 display is set to zero with the plunger 32 in its normally extended position and the moveable jaw 18 in contact with the fixed jaw 14. The workpiece A is placed between the moveable jaw 18 and the fixed jaw 14 and the moveable jaw 18 is released. As shown in Fig. 1, since the plunger 32 is spring biased in a normally extended position, the plunger 32 pushes against the moveable jaw 18, causing the moveable jaw 18 to slide into contact with the workpiece A. The displacement of the plunger 32, and therefore the length or thickness of the workpiece A, may be read directly from the indicator 30 display.

Preferably, the frame 11 is made from hardened tool steels with a black oxide finish, the jaws 14 and 18 being precision ground, except for the uprights and the crossbar 26, which are made from stainless steel, and the dust shield 22. Because of the small force exerted by the plunger 32 against the moveable jaw 18, the pressure exerted against the face of the workpiece A is also very small and approaches zero. If desired, the pressure exerted against the face of the workpiece A may be increased up to about one hundred ounces by altering the angle of the base plate 12 with respect to horizontal from zero to ninety degrees. The measurement may be repeated or reproduced with precision, provided the base plate 12 is at the same angle with respect to horizontal. In order use the measuring instrument 10 to measure depth, the instrument 10 is placed in a vertical position with the fixed jaw 14 laid flat against a horizontal surface as shown in Fig. 3. The moveable jaw 18 lies flat on top of the fixed jaw 14 both because of the spring bias of the plunger 32 and by gravity. The workpiece B is placed on the moveable jaw 18, the plunger 32 is retracted, placed against the outer surface of the workpiece B, and the indicator 30 display is set to zero. The workpiece B is then moved to place the inner surface of the workpiece B, e.g., a hole, edge cut or the like, under the plunger 32, and the spring bias of the plunger 32 forces the tip of the plunger against the inner surface. The displacement of the plunger 32, which also indicates the depth of the hole, edge cut, etc., is read directly from the indicator 30 display.

It is to be understood that the present invention is not limited to the sole embodiments described above, but encompasses any and all embodiments within the scope of the following claims.

Claims

CLAIMSWe claim:

1. A measuring instrument for measuring the length, thickness or depth of a workpiece, comprising: a) a frame having a fixed jaw and a moveable jaw, said moveable jaw being slidably mounted on said frame; b) bias means for resiliently biasing said moveable jaw into contact with said fixed jaw; and c) displacement measuring means mounted on said frame for measuring the displacement of said bias means when said moveable jaw is displaced from contact with said fixed jaw.

2. The measuring instrument according to claim 1, wherein said bias means comprises a plunger of a digital indicator, said plunger being spring biased in a normally extended position.

3. The measuring instrument according to claim 1, wherein said displacement measuring means comprises a digital indicator.

4. The measuring instrument according to claim 1, wherein said frame further includes: a) a base plate, said fixed jaw being attached to said base plate; b) a top plate, said moveable jaw being attached to said top plate; and c) a slider mechanism, said slider mechanism being attached to said base plate and said top plate.

5. The measuring instrument according to claim 4, wherein said frame further comprises: a) a pair of uprights mounted on said base plate; b) a crossbar mounted between said uprights and disposed above said top plate; and c) a collet mounted on said crossbar, the collet being adapted to receive and support said bias means and said displacement measuring means.

6. A method for using the measuring instrument according to claim 1 in order to measure the length or thickness of a workpiece, comprising the steps of: a) placing the measuring instrument on a flat, horizontal surface with the frame at an angle between 0┬░ and 90┬░; b) setting the displacement measuring means to indicate a displacement of zero; c) placing the workpiece between the moveable jaw and the fixed jaw; and d) reading the displacement shown on the displacement measuring means.

7. A method of using the measuring instrument according to claim 1 in order to measure the depth of displacement between an inner surface and an outer surface of a workpiece, comprising the steps of: a) placing the measuring instrument on a flat, horizontal surface with the fixed jaw flat against the horizontal surface; b) placing the workpiece on top of the moveable jaw; c) placing the bias means in contact with the outer surface of the workpiece; d) setting the displacement measuring means to indicate a displacement of zero; e) placing the bias means in contact with the inner surface of the workpiece; and f) reading the displacement shown on the displacement measuring means.