FR2624420A1 - METHOD FOR MONITORING THE WORKING PROCESS OF A MACHINE TOOL - Google Patents

Abstract

The object of the present invention is a method for monitoring the work of a machine tool, intended to detect harmful influences by measuring the evolution of the current consumption, mainly characterized in that in addition to the current consumption one measurement of other parameters from which it can be inferred whether the corresponding state of the machining process is acceptable or not, and in that measures are taken to stop the machine tool if a certain maximum value is exceeded , and that the maximum value is modified according to the state of the process.

Description

The subject of the invention is a

  process for monitoring the work of a machine tool.

In this case, it's all

  simply to check whether a machine tool is working properly

  or not, in order to be able to possibly take measurements. A defective job can have the most diverse origins. The most important origin is the blunt state of the tool. Defective operating conditions are noted by an increase in the current consumption of the advance control concerned. In this case, the current generally rises, before the influences

  have caused serious damage. If for example, the

  til becomes more and more blunt during the machining of a workpiece, the current rises until the arrival at a certain maximum value, voluntarily set. Upon reaching this maximum value, the machine tool is stopped, which can

  do it either by hand or automatically.

  At the same time, we will generally have installed a safety stop as protection against

  overloads. After stopping the machine tool, you can then

  you, in general, easily discover the origin of the rise

  current and thus harmful influence, and remedy it.

  In practice, there has hitherto been a problem in that the safety stop did not respond at the appropriate time. In general, the safety stop should not operate too early, but not too late, or in other words: the setpoint should not be too high, but not too low. If it is too

  high, there is the danger of the appearance of damage.

  If, on the other hand, it is too low, this often means a false alarm, that is to say a triggering of the stop.

  without real reason, which reduces the yield. Juice-

  that here this problem has not been solved: it has above all always been revealed that the safety stop responded without any real inconvenience, and that all the components were in a faultless state

  and that the cutting edge of the tool was sharp.

  The object of the invention is to propose a monitoring method, so that the monitoring works more precisely than before, that is to say with greater discrimination precision in order to be able to reduce the tolerance margin. of the stop reaction. This problem is solved by a method characterized in that in addition to the current consumption, other parameters are measured from which it can be deduced whether the corresponding state of the machining process is acceptable or not; in that we take steps to stop the

  machine tool if a certain maximum value is exceeded

  male, and in that the maximum value is modified according to the state

of the process.

It is advantageous for the utlllsa-

  tion of the method according to the invention to equip the machine tool concerned with a direct displacement measurement system and / or

indirect, incremental.

  To carry out the invention it may be necessary to insert a precision resistor in the circuit of the control motor, which may be part of an axle gear or of a spindle control. Such

  However, the controls often have an outlet which provides

  denies current consumption. Generally a microprocessor with a logical recording for measurement systems

  displacement and A / D converters will be required.

The necessary parameters can be

  can be captured by dual use of the outputs of the measurement systems. This means that by direct entry

  position without additional sensors, it is possible

  Enter the speed and acceleration of the axis or spindle to be monitored. In addition the A / D converter

measures the current values.

Then there is a micro-oralna-

  tor which is able to record a current value, by axis or by spindle, at determined time intervals, for example every hundred mico-seconds, and which, every twenty millisecond, from this value , form a value

  mean using elimination of "implausible values".

  On the basis of the parameters then entered, all sets according to the invention, that is to say current, position, speed, acceleration and possibly also deformation values, the conditions can be differentiated unacceptable acceptable conditions. The computer is used for this purpose,

  entering values according to certain interrogation strategies

  and comparing them with the stored data.

iO The process according to the invention

  thus makes it possible, as already indicated, to recognize and dis-

  identify non-tolerated process conditions, such as

example:

  - the wear of the tool, - the chipping of the cutting edge of a tool, - the total breakage of a tool, - a defect in the digital comma.anae by computer, - a false operation, for example: a wrong axis selection or too much speed

high in advance.

  Since the method of the invention can operate without force detectors, it is also suitable

  for retrofitting already existing machine tools.

Furthermore, the method of the invention

  tion is suitable for diagnosing the condition of machines,

  such as, for example, the state of the guide bearing or the adjustment of

order formers.

  Naturally, the system is also able to take setpoint data from the CNC control to concretize the database values on this basis. An example could be the distinction between wear and tear to which a larger drill is subject by

  compared to the wear to which a smaller drill is subject.

  In this way it is possible to change basic values

  as setpoints for a certain tool.

  In this context, the inventor recognized the following facts: Apart from the indicated influences which have to some extent harmful effects (poor surface of the workpiece, high forces not tolerated which influence the machine tool, etc.) and which increase the consumption of the current, we know still other influences

  which modify the consumption of the current, but which are perfect

  harmlessly. Among these influences are the changes

  cations of the speed of advance, acceleration, composition of the material, etc. On the basis of these facts, the inventor recommended not only to enter the overall consumption

  of current but in addition to it, the parameters that are harmless

  but which also influence current consumption.

  i5 The most important of these parameters are speed and speed.

leration of the advance.

In practice, some displacements

  cements are quite typical of a machine. In this case, it is for example very clearly shown that the acceleration

  and the current consumption of an advance control is

  always try to be proportional to each other. This means that the current rises considerably in the event of an acceleration of the advance. Braking has like

  normal consequence, a counter current in the advance motor.

  The machine is braked by the negative acceleration that appears.

  In this case, also the current and the acceleration evolve in

  the same way. The acceleration of the advance is quite usual

  trowel for the work of a machine tool. In general it is wanted. As shown, it has an influence on current consumption. Thus it represents a datum of typical influence, which at the same time is harmless, in the spirit of the invention, and yet influences consumption

current.

  The invention is explained more fully with the aid of the diagrams of the attached plates in which:

- fig.1 shows schematically

  only changes in the speed of acceleration of a tool as well as current consumption; in this case, the changes in current consumption are based on harmless influences, - fig.2 shows diagrams similar to those in fig.1; in this case, the changes in current consumption are however based on

harmful influences.

  read - fig.3 shows a diagram of actual speed and acceleration recording of a feed

  as well as the current consumption of the advance control.

  In fig.l, the influence of the acceleration of the tool is shown (upper diagram)

  as well as braking (lower diagram). In this case, access

  leration has been designated by a, speed by v, and consumption

  tion of current by 1. As can be seen in the dia-

  gram higher, the current consumption increases suddenly as soon as the speed increases, with constant acceleration but with an increase in speed, and remains at a constant value throughout the rise. After reaching maximum speed and constant speed maintenance, consumption

  of the current decreases a little and then also remains constant.

A corresponding finding

  can be done on the lower diagram.

  The diagrams shown in fig. 2 show influences which are characterized as

  harmful in the sense of this invention. In the upper part

  The vertical dashed line indicates when the drill became unusable due to chipping of the cutting edge. As can be seen, sudden braking takes place the acceleration is thus lowered to a certain value, on which it remains constantly. Speed decreases

constantly from that moment.

Even more significant is

  the influence of a shock according to the diagram below.

  The diagram represented in fig. 3 again shows the three data a (acceleration),

v (speed) and I (current).

First we see in the representation

  feeling to the left of point 1, the tool stopped. Acceleration and speed are approximately zero, while

  the current oscillates slightly, to maintain the state.

  After a short time, the tool begins its movement, which is expressed by an increase in

  three data in the diagram. At 2, the current and the acceleration

  tion reach a maximum, which at the same time represents a point of return. The acceleration then drops to a minimum of 3, rises to a maximum of 4, etc. This method represents a balancing which is based on the fact that in this case the amplifier of

  the order was not adjusted optimally.

  The speed on the other hand increases in the first rising section even more than the acceleration and the current. It finally reaches a value for 5 which

  is first maintained more or less constantly.

At point 6-6 something important

  bearing then occurs: for the purposes of the test, a shock was simulated in which a tool struck a workpiece at too high a speed. In this case, provision was made so that the machine could not be seriously damaged. The consequence of this shock can be clearly recognized: the acceleration falls sharply and reaches a minimum out of 7. At the same time the current increases strongly and reaches a maximum out of 8. As we can see, it follows an increase in l acceleration to the value 9. This rise is based on the fact that the static friction of the workpiece on its support has been overcome, and that

  the workpiece was then pushed at an essential speed-

  slightly equal. As we can see next, this is only possible for a certain time, because point 9 represents at the same time a point of return; acceleration then decreases

  again, as we can see.

To be complete, you must

  quer that the evolution of speed v has not been represented

  for reasons of measurement techniques, as it happened

  lée in reality. Speed does not play a role in this, however.

text as a supporting role.

  Thanks to the invention it is possible, as can be seen, to recognize these different stages on the line 6-6 of resistance. From this knowledge we can naturally, when all this was not possible before, immediately introduce corresponding measures

  which can of course also be automated.

REV E N D I C A T I O N S

  1.- Method for monitoring the progress of the work of a machine tool, intended to grasp harmful influences by measuring the evolution of current consumption, characterized: in that in addition to current consumption we measure d other parameters from which it can be deduced whether the corresponding state of the machining process is acceptable or not, in that measures are taken to stop the machine tool if a certain maximum value is exceeded, and that the maximum value is changed according to the state of the process; 2.- Method according to claim 1, characterized: in that the position of an axis, the speed, the acceleration, the deformation of the control system, etc. are entered as other parameters, either separately , or together;

  3.- Method according to one of claims 1 to 2, characterized:

  in that the difference between measurement results from a direct and indirect measurement system (displacement measurement input system)

  is used as another parameter.