DESC:MEASURING INSTRUMENT FOR PRECISION MACHINES

FIELD OF THE INVENTION

The present invention relates to a measuring instrument and more particularly, to the measuring instrument for precision machines that does not suffer from contraction or expansion of a scale in response to temperature changes.

BACKGROUND OF THE INVENTION

Precision machining of an object involves measuring the dimensions like length, diameter etc of the object using a scale and a sensor with accuracy and precision. At present, the scale in a measuring instrument is glued on a guide way or is kept free floating in a track. The glued scale expands/contracts with changes in surrounding temperature as well as changes in the temperature of the guide way. Such expansion or contraction in the scale causes error in dimension measurement thereby leading to erroneous machining.

Accordingly, there is a need of a measuring instrument that overcomes the above mentioned drawbacks of the prior art.

OBJECTS OF THE INVENTION

An object of the present invention is to minimize or prevent expansion/ contraction of a measurement scale due to changes in surrounding and/or guideway temperature(s) to achieve errorless measurements.

SUMMARY OF THE INVENTION
Accordingly, the present invention provides a measuring instrument for a precision machine. The measuring instrument comprises a substrate member, a scale, a guideway, a spring, fasteners, a sensor and a decoder.

The substrate member is a high modulus substrate member made from a material for example a carbon fiber strip having minimum/zero coefficient of thermal expansion.

The scale is fixed for example by firmly gluing on the substrate member. The scale includes a scale clamp and a scale reference marked thereon.

The substrate member with the scale together with the spring is assembled on the guideway using the fasteners for example screws and loaded screws. The spring is a compression spring clamped by a spacer. The spring along with a roller compresses the substrate member on the guideway. The guideway is made up of a material selected from any one of aluminium, cast iron, mild steel, granite and combinations thereof.

The sensor selected from any one of a linear encoder, a transducer and a redhead is configured with the substrate member to encode a position. The sensor reads the scale to convert the encoded position into any one of an analog signal and a digital signal.
The decoder selected from any one of a digital readout and a motion controller is configured to decode the analog/digital signal into the position.

When there is a change in the temperature, the guideway expands while the substrate member and the scale do not undergo expansion or contraction thereby providing measurement without any error.

BRIEF DESCRIPTION OF THE DRAWINGS

The objectives and advantages of the present invention will become apparent from the following description read in accordance with the accompanying drawing wherein,
Figure 1 shows a view of a measuring instrument for precision machines, in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The foregoing objects of the present invention are accomplished and the problems and shortcomings associated with the prior art are overcome by the present invention as described below in the preferred embodiment.

The present invention provides a measuring instrument for precision machines. The measuring instrument includes a scale glued on a high modulus substrate material having low coefficient of thermal expansion as compared to other substrate materials to minimize or prevent the expansion/ contraction of the scale due to changes in surrounding and/or guideway temperature(s) to achieve errorless measurements.

The present invention is illustrated with reference to the accompanying drawings, throughout which reference numbers indicate corresponding parts in the various figures.

Referring now to figure 1, there is shown a measuring instrument (100) for a precision machine (not shown) in accordance with the present invention. In a preferred embodiment, the precision machine is a co-ordinate measuring machine (CMM). However it is to be understood that the measuring instrument (100) can be used for any other precision machines known in the art as per various alternate embodiments thereof. The measuring instrument (100) comprises a substrate member (10), a scale (20), a guideway (30), fasteners (40), a spring (50), a sensor (60) and a decoder (not shown).

The substrate member (10) is a high modulus substrate member, made from a material having minimum/zero coefficient of thermal expansion. Specifically, the substrate member (10) is made from a carbon fiber strip having the coefficient of thermal expansion minimum/zero/less than other material to be used as guideways. In alternate embodiments, the substrate member (10) can be made from materials having coefficient of thermal expansion minimum or zero, for example, Invar, Robax and the like.

The scale (20) is fixed on the substrate member (10). The scale (20) includes a scale clamp (12) and a scale reference (14). Preferably, the scale (20) is firmly glued on the substrate member (10). However, the scale (20) can be fixed on the substrate member (10) using any other suitable means known in the art.

Once the scale (20) is glued on the substrate member (10), the substrate member (10) is assembled on the guideway (30) together with the spring (50). In an embodiment, the spring (50) is a compression spring clamped by a spacer (80). The spring (50) along with a roller (70) is adapted to compress the substrate member (10) on the guideway (30). The guideway (30) is made up of a material selected from but not limiting to any one of aluminium, cast iron, mild steel, granite and combinations thereof.

When there is a change (either an increase or decrease) in temperature of the guideway (30), the guideway (30) expands while the substrate member (10) and the scale (20) do not undergo expansion or contraction thereby providing measurement without any error.

The fasteners (40) are adapted for fixing the substrate member (10) together with the spring (50) on the guideway (30). In an embodiment, the fasteners (40) are screws. In a preferred embodiment, the fasteners (40) are loaded screws.

The scale (20) on the substrate member (10) is paired with the sensor (60) that encodes position. The sensor (60) is configured with the substrate member (10) to read the scale (20) in order to convert the encoded position into an analog or digital signal which can be stored. In an embodiment, the sensor (60) is a linear encoder, a transducer or a redhead. The linear encoder for example incremental or absolute are used in metrology instruments, motion systems and high precision machining tools ranging from digital calipers and coordinate measuring machine to stages, CNC Mills, manufacturing gantry tables and semiconductor steppers. The linear encoder technologies include optical, magnetic, inductive, capacitive, eddy current and the like. Optical technologies include shadow, self imaging, interferometric and the like.

The analog or digital signal is then decoded into the position by the decoder. The decoder is selected from any of a digital readout (DRO) and a motion controller. Motion is determined by change in position over time.

ADVANTAGES OF THE INVENTION

The scale (20) being glued on the substrate member (10) made up of carbon fiber material that have minimum/zero coefficient of expansion undergoes minimum / zero expansion / contraction in response to changes in the temperatures of the surrounding and the guideway (30) thereby resulting in minimum / zero error in scale measurement.

The foregoing objects of the invention are accomplished and the problems and shortcomings associated with prior art techniques and approaches are overcome by the present invention described in the present embodiment. Detailed descriptions of the preferred embodiment are provided herein; however, it is to be understood that the present invention may be embodied in various forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but rather as a basis for the claims and as a representative basis for teaching one skilled in the art to employ the present invention in virtually any appropriately detailed system, structure, or matter. The embodiments of the invention as described above and the methods disclosed herein will suggest further modification and alterations to those skilled in the art. Such further modifications and alterations may be made without departing from the spirit and scope of the invention.
,CLAIMS:WE CLAIM:

1. A measuring instrument (100) for a precision machine, the measuring instrument (100) comprising:
• a substrate member (10) made from a material having minimum/zero coefficient of thermal expansion;
• a scale (20) fixed on the substrate member (10), the scale (20) having a scale clamp (12) and a scale reference (14) marked thereon;
• a guideway (30) having the substrate member (10) with the scale (20) assembled thereon;
• a spring (50) assembled on the guideway (30) together with the substrate member (10), the spring (50) along with a roller (70) compresses the substrate member (10) on the guideway (30);
• fasteners (40) fixing the substrate member (10) together with the spring (50) on the guideway (30);
• a sensor (60) configured with the substrate member (10) to encode a position, the sensor (60) reads the scale (20) to convert the encoded position into any one of an analog signal and a digital signal; and
• a decoder configured to decode the analog/digital signal into the position,

wherein, when there is a change in the temperature, the guideway (30) expands while the substrate member (10) and the scale (20) do not undergo expansion or contraction thereby providing measurement without any error.

2. The measuring instrument (100) as claimed in claim 1, wherein the substrate member (10) is a high modulus substrate member made from a carbon fiber strip having minimum/zero coefficient of thermal expansion.

3. The measuring instrument (100) as claimed in claim 1, wherein the scale (20) is firmly glued on the substrate member (10).

4. The measuring instrument (100) as claimed in claim 1, wherein the guideway (30) is made up of a material selected from any one of aluminium, cast iron, mild steel, granite and combinations thereof.

5. The measuring instrument (100) as claimed in claim 1, wherein the spring 50) is a compression spring clamped by a spacer (80).

6. The measuring instrument (100) as claimed in claim 1, wherein the fasteners (40) are screws.

7. The measuring instrument (100) as claimed in claim 4, wherein the screws are loaded screws.

8. The measuring instrument (100) as claimed in claim 1, wherein the sensor (60) is selected from any one of a linear encoder, a transducer and a redhead.

9. The measuring instrument (100) as claimed in claim 1, wherein the decoder is selected from any one of a digital readout and a motion controller.