Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B5/00—Measuring arrangements characterised by the use of mechanical techniques
  • G01B5/0011—Arrangements for eliminating or compensation of measuring errors due to temperature or weight
  • G01B5/0014—Arrangements for eliminating or compensation of measuring errors due to temperature or weight due to temperature

Definitions

• the measuring accuracy of a coordinate measuring machine is very strongly influenced by the ambient temperature and the temporal and spatial temperature gradient in the area of the machine.
• Coordinate measuring machines are therefore mainly used in measuring rooms that are air-conditioned to a constant reference temperature of 20 ° C and in which the temporal and spatial temperature gradients are maintained at less than 0.5 ° C per hour or 0.5 ° C above the measuring range of the machine are. If the coordinate measuring machine has a device for arithmetically correcting its guiding errors, the correction data created during machine acceptance also apply only under the above-mentioned conditions.
• the correction data sets (KT) required for the correction of the guide error are determined at several different temperatures (T 1 ... T n ) and stored in the computer of the coordinate measuring machine,
• the coordinate measuring machine is surrounded by a heat-insulating encapsulation and air is blown into the encapsulation
• the temperature is measured at a representative point and is used to select the current correction data set (T E ).
• the heat-insulating encapsulation significantly reduces convection, heat conduction and heat radiation and thus also the change in temperature gradients in the machine.
• a sufficiently high air throughput through the encapsulation and defined entry and exit points for the blown-in air mean that the existing temperature gradients only depend on the temperature T at a representative point and not on other, not measurable ambient conditions. This is the prerequisite for a reproducible dependency of the systematic machine errors on the measured temperature and allows correction data sets for different temperatures to be set up and used in the subsequent measuring operation.
• the representative location the temperature of which is decisive for the selection of the correct correction data record, depends on the design of the coordinate measuring machine used and is determined experimentally for the machine type, for example. Alternatively, it is possible to measure the temperature of the air blown in at the air inlet point and then make a delayed selection based on this temperature value.
• Fig. 1 is a perspective view of the
• FIG. 2 is a block diagram to illustrate the processing of measured values in the computer of the coordinate measuring machine from FIG. 1;
• 3 is an exemplary representation of a part of the data fields used for the measured value correction.
• the coordinate measuring machine (1) shown in Fig. 1 is set up within a rectangular cabin (2), the side walls, floor and ceiling of which are made of heat-insulating material. On the front there is a sliding window (7) through which the workpieces can be fed and the measuring process can be observed.
• a blower (3) is located above the cabin (2). This fan sucks in ambient air through a nozzle (4) and blows this air into the cabin, where it exits through the fins (6) at a defined point.
• a temperature sensor (5) at a representative point on the coordinate measuring machine (1) is used to measure the temperature T E.
• the temperature of the sucked-in air is changed step by step, for example between 18 ° C and 26 ° C, in steps of 2 ° C and kept constant at the respective value with the help of an upstream air conditioning device that is only required.
• the temperature is measured using the temperature sensor (5) on the coordinate measuring machine.
• the systematic machine errors are determined for each preset temperature, ie the translational and rotatori see guide errors of the three measuring axes x, y and z according to known measuring methods.
• the data obtained in this way are stored in the memory (9) of the computer of the coordinate measuring machine designated by (4) in FIG. 2 for correcting the measurement results.
• the blower (3) draws in the non-air-conditioned ambient air through the nozzle (4).
• the thermal sensor (5) measures the temperature on the coordinate measuring machine and passes this measured value T E on to the computer (4) of the coordinate measuring machine.
• the computer (4) selects the associated data record KT E from the data field stored in the memory (9) and corrects the coordinate measured values x, y and z taken from the scales (11, 12, 13) of the measuring machine (1) .
• the corrected measured values x ', y', z ' are then shown on the display (10) of the computer.
• the temperature at the measuring point lies between two temperatures for which correction data sets are stored, then a data set formed by interpolation from the adjacent correction data sets is expediently used by the computer.
• the measuring point itself, to which the temperature sensor (5) is attached, was determined experimentally and corresponds in its time behavior, with which it follows temperature changes in the environment, to the time behavior which the supporting parts and guides relevant for the machine geometry have.
• the method described above can also be combined with a correction method for the error which arises due to different scale temperature and the temperature of the workpiece to be measured, if this is described in the earlier application P 36 20 118.9 procedure and additionally determines the temperatures of the workpiece to be measured on the coordinate measuring machine and the scales of the coordinate measuring machine and uses them to correct the coordinate measured values to a level applicable to a fixed reference temperature of, for example, 20 ° C.
• the combination of both correction methods is even particularly advantageous for production-related use of the coordinate measuring machine, since usually both error influences, undefined ambient temperatures and an undefined workpiece temperature, occur simultaneously.
• the temperature sensors Tx, y, z necessary for carrying out the method described in the earlier application are attached to the scales (11, 12 and 13) of the coordinate measuring machine in FIG. 1.
• the temperature of the workpiece or its deviation from the reference temperature is expediently determined, as explained in P 36 20 118.9, by means of a length measurement on a reference body (gauge block) of a defined length, which has passed through the manufacturing process together with the workpiece and has therefore assumed its temperature.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Length Measuring Devices With Unspecified Measuring Means (AREA)

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• 1986
  • 1986-09-19 DE DE19863631825 patent/DE3631825A1/de not_active Withdrawn
• 1987
  • 1987-09-03 WO PCT/EP1987/000497 patent/WO1988002096A1/de not_active Application Discontinuation
  • 1987-09-03 JP JP50560387A patent/JPH01500853A/ja active Pending
  • 1987-09-03 EP EP19870906177 patent/EP0285624A1/de not_active Withdrawn

Non-Patent Citations (1)

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