Data processing: generic control systems or specific application – Specific application – apparatus or process – Product assembly or manufacturing
Reexamination Certificate
1994-09-16
2001-03-20
Grant, William (Department: 2121)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Product assembly or manufacturing
C700S164000, C700S193000, C702S035000, C318S567000, C073S593000
Reexamination Certificate
active
06205371
ABSTRACT:
The invention deals with a method and an apparatus for detecting machining flaws caused by machine tools mechanically removing material from surfaces, especially by grinding machines.
BACKGROUND OF THE INVENTION
A number of mechanical machining processes exist, where flaws can occur on the surfaces of workpieces and which cannot be detected at all or only with great effort, in spite of the fact that such flaws can result in final destruction or failure if the flawed workpieces are used for long periods. Typical examples are, for instance, heat checks and grinding checks in workpieces finish-machined by grinders, such as shafts, gear wheels or the like. Flaws which do arise can have different reasons or origins. They can be caused by workpiece tolerances, by positioning errors, by differing workpiece hardness and naturally by the condition of the tool bit, for instance by the condition of the grinding disc.
Such work processes are automated precisely in mass production, which entails that basically each machined workpiece must be subsequently inspected, in order to avoid later failure of the workpieces due to these machining defects, or in order from the start to eliminate such defective workpieces. Such an inspection is naturally very expensive.
SUMMARY OF THE INVENTION
Thus an object of this invention is a solution by means of which the occurrence of such machining flaws can be detected directly during the machining process of the workpiece itself, in such a way that either the workpiece is identified as being flawed or however counter or corrective measures are made possible. Possible measures include, for instance, increasing or decreasing the feed or drive velocity of a grinding tool.
This object is achieved in accordance with one aspect of the invention in the process of the previously described type in such a way that the force applied by the tool bit upon the workpiece is measured in the course of the machining process as an “actual or instantaneous” value, this value being fed to an electronic data processing arrangement and is there compared with a “nominal” value stored there and that the obtained values are documented.
It would seem that the flaw sources indicated above directly lead to an increased force applied by the tool bit to the workpiece. If, for instance, the workpiece is too large in the machining region due to workpiece tolerances, a larger amount must be removed by grinding, which is immediately reflected in a higher grinding force with a grinding disc with automatic feed. If the workpiece is incorrectly positioned in the workpiece receptacle, a similar error can occur. If the wrong workpiece hardness is present in the machining region, this again results in an increased force with a grinding disc having automatic feed. If for instance the grinding disc is glazed or clogged, possibly the force exerted on the workpiece must be increased for removal of a predetermined amount of surface material. The determination of all these possible sources of error and with this the increase of the force exerted by the tool bit upon the workpiece can be performed without any problems by means of the invention.
In accordance with a further feature of the invention, the grinding force can be measured directly at the tool bit spindle or indirectly by the deformation of the tool bit receptacle, wherein it can be especially provided that the grinding force is measured in a contactless manner by high resolution inductive path pick-ups at the tool bit receptacle. The invention also provides for the utilization of accelerometers independent of reference points at the tool bit receptacle instead of inductive path pick-ups, or for the use of reference point free accelerometers in combination with path pick-ups. It was observed that in certain machining processes using accelerometers, the dynamic excursion, be it of the workpiece, the tool bit or the workpiece receptacles, can be measured. Reference curves can be prepared with these vibration pick-ups, with which then the momentary or actual curve can be compared.
A simple procedure in accordance with a preferred embodiment of the invention consists in machining first of all a workpiece in accordance with the machining program and to determine and store all actual or momentary values during the entire time period. If the workpiece is determined to be free of flaws after individual very detailed inspection, the thus determined actual values are stored in the computer as the nominal values and are electronically processed during subsequent machining of identical workpieces.
It is known in profile grinding machines to simultaneously grind for instance two tooth flanks. In order to avoid detecting an error on the one side in a more than proportional manner and to thus utilize same, the invention provides to use at least two inductive path pick-ups located at an angle with respect to each other for measuring the grinding force, wherein the measured signals are digitized, stored and filtered in two channels. With this it is possible to avoid flaws in the data acquisition cycle. If for instance only one tooth flank is excessively machined due to warping of the workpiece, it is possible to fail to detect this in case of a one-dimensional measurement. Here it is expedient to compare the individual and the overall values with their respective limit values in a “two-dimensional” manner.
It should be noted that the same type of measurement can naturally also be performed three-dimensionally in the invention. Then, appropriately three measured value pick-ups are provided.
The invention also provides to centrally control the grinding processes, especially the feed and drive velocity of the tool bit by means of the measured value acquisition, wherein it can be provided in another refinement that all measured signals are printed out by a printer in the form of curves or measured value columns.
It is known for instance from the DE-81 21 451-A to measure vibrations of machine tools in order to prevent these from being damaged. A tool bit failure monitoring is for instance also known from the DE-37 11 434-A. However, with these references, no flaws at workpieces to be machines are established or recorded, rather merely unusual events at the tool bits or the machine tools.
The invention also provides a device for solving the task stated above which is distinguished by at least one measured value pick-up recording the force between the tool bit and the workpiece, in cooperation with an assigned electronic data processing installation. The design uses the knowledge that, for instance, heat checks occur with an excessive grinding force, wherein then an elastic deformation of, for instance, the tool bit receptacle or the tool bit spindle occurs with reference to the machine foundation. According to the invention, figures in the range of 5 to 15 micrometers being a function of the grinding force can be determined in a measuring axes region.
The invention however also provides two measured value pick-ups operating in a contactless manner at the tool bit receptacle and/or at the tool bit driving spindle, whose effective measuring axes are at an angle to each other, so that it can be in particular provided that high resolution inductive path pick-ups operating in a contactless manner and/or accelerometers operating without reference points are provided as measured value pick-ups.
It is advantageous if an electronic amplifier, a filter and an A/D-converter is assigned to each path pick-up for the purpose of transmitting the measured value to a central processing unit, as this is also provided in the invention. The device is finally also distinguished in that it is equipped with at least one storage means for storing of a nominal value, a predetermined normal grinding curve and an actual or momentary value.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects a
Brown & Wood LLP
Grant William
Rao Sheela S.
LandOfFree
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