DD297593A5 - METHOD FOR THE AUTOMATIC DETERMINATION OF A KNOWLEDGE FOR CONTROLLING THE METHOD OF PROCESSING WHEN GRINDING WITH MEASUREMENT CONTROL DEVICE - Google Patents

Abstract

On the basis of the automatic Kenngroesze on the one hand by an adaptive control of the procedure (adaptation of Ausfunkaufmaszes) the required workpiece accuracy with improved efficiency (shortening of the grinding time) ensured, on the other hand the Verschleiszzustand the Schleifkoerpers (dulling, Selbstschaerfung) in similar workpieces (constant system stiffness) in mass production (trend monitoring). According to the invention, the characteristic quantity is determined from the continuous output signal of a measuring control device. Meszsteuereinrichtung; in-process measurement; adaptive control; Trendueberwachung; Life end}

Description

For this 2 pages drawings

The invention relates to a method for determining a parameter for the control of the procedure during the Grinding with measuring control device. Dio determined parameter is related to the system deformation during grinding and grinding behavior

(Cutting ability) of the abrasive article. The main area of application is grinding in the metalworking industry. On the basis of the determined parameter, an adaptive control of the

Procedure for grinding and / or an assessment of the grinding or wear behavior of the grinding wheel

done what u.a. constitute essential prerequisites for the economic application of the grinding process under conditions of flexible, low-service production.

The grinding process is unsteady due to finite system stiffness and abrasive wear. The

means that during grinding caused by the deformation system deformation significant differences between the

Feed rate of the wheelhead (nominal feed rate) and the speed of the wheelhead Radius decrease of the workpiece (real feed speed) exist. For reasons of economy and machining accuracy, the grinding process is usually in multi-stage Grinding cycles, which consist of the phases roughing, finishing and / or sparking performed. The Roughing phase is used for fast grinding of a large portion of the oversize. The finishing and sparking phases should

Reduce the action deformation and lead to the improvement of the dimensional and form accuracy and the workpiece roughness.

As a result of wear-related changes in the abrasive active surface different forces occur and thus

different system deformations. Due to this, despite the use of measuring control devices on

Uneven real feed velocities before, the dimensional and form errors as well as a fluctuating Result in workpiece roughness. These effects can be reduced by increasing the feed rate in several ways Steps is reduced to very small values, but this is done at the expense of cost-effectiveness. Other solutions of the

have been described in various patents.

In DE 2756642 a system tension is achieved by retracting the abrasive body after the roughing phase

is to achieve a constant real sizing feed rate, wherein the measurement of the Zeitspanvolumens in the

Simple phase on the torque or the force takes place. A disadvantage is the measurement uncertainty, since different states of the abrasive active surface at the same real Feed rates e.g. give different sized forces. According to DE-OS 2913682 a basic measurement on

pre-ground workpiece, whereby the abraded oversize is determined as a result of the system deformation and can be entered as Ausfunk-oversize in the control.

The disadvantage of this solution lies in the necessary interruption of the procedure. In DD-WP104249 and DE-OS 2519735 the system deformation is calculated directly as the difference of the measured values of a measuring system on Grinding headstock and the measuring control device measured and used to control the feed movement, wherein

However, an increased equipment costs results.

The devices described in the patents DE-OS 3021493 and DE 1289452 also relate to the grinding Measuring control device and measuring system. The signal difference (active system deformation) determines the regulation of the Zustellantriebes, so that the real feed speed is in certain preselectable tolerances. Similar solutions

are given in CH-PS 337090.

Basis of the patent DD 240513 is the determination (calculation) of an accuracy-based spark-out time (number of Spark rotations of the workpiece) on the basis of the signal difference of the position measuring system and Moßsteuereinrichtung.

To assess the state of wear or to detect the service life of the grinding wheel also different solutions are known. These are based on optoelectronic sensors, on the vibration measurement or the measurement of the stress force or related variables such as:

- Signal difference between measuring system and Meßsteuoreinrichtung (DE 3529427, DE 053021493)

- Current measurement on the grinding spindle drive, time measurement for a given dimensional change, corresponding to the real feed rate (DBP 1023362).

The current measured values are compared with those immediately after the dressing process. When crossing

given limit values is the display of the end of life or, triggering the dressing process.

Common to all solutions is the flexibility of the relatively high equipment complexity (additional Measuring systems).

The aim of the invention is to develop a method and to provide a device, which is determined from the continuous output signal of a measuring control without additional sensors and with relatively little effort, a parameter that can be used for adaptive control of the process sequence during grinding or the evaluation the grinding or wear behavior or the detection of the service life end of the grinding body allows. The invention has for its object to provide a method which is the basis for the development of a M '^ device arrangement, with a characteristic is determined exclusively from the continuous output of a Melisteuereinrichtung that for adaptive control of the process sequence during grinding and / or Assessment of the grinding behavior or the state of wear of the grinding wheel can be used. From the literature, approaches for the mathematical description of quantities that characterize the transient process sequence in grinding or spark-out phases (time course of the forces, the system deformation, the real feed rate or the real feed path (see FIG. 1) are known.

An analytical description is possible based on a linearization of the deformation behavior fo "= f (F _v ) and the dependence of the feed force on the real feed rate F _v = f (v ₍ ", i).

It can be written with it:

foe »= Ifnom - Ifiul = ^ v M)

Coei

F _v = α · b _s ν ,,,,, (2)

fge · · · · System deformation

Ifnom ... nominal feed path

! ("Al ... real feed path

Co, ... system stiffness (total stiffness) at the machining point Fv ... feed force

b _s ... grinding width

α ... coefficient for the cutting ability of the grinding wheel

Vfreai ... real feed rate

From the equilibrium of forces [GL (D and (2)] one obtains a differential equation, from the solution of which the relations to the description of the temporal course of the real feed speed or of the real feed path result.

Anschlolf phase:

Vf ".i = v_(nom · (1 - e -γ) (3)

Ifre.l = V _(nom · t - T · V _(nom · (1 - β - -) (4)

Spark-out phase: Vfnom " t •(1 - e -7 " Vf,., I = C + T · Vfnom Unreal -

Vfnom ··· nominal feed rate

t ... time

C ... Constant (corresponds to the real feed path traveled in the roughing phase)

s, ... plunge feed

n _w ... workpiece speed

The parameter T (time or delay constant) is dependent both on the system stiffness C ₀ ,, the grinding width b _s and on the coefficient of cutting ability of the grinding body α:

(7)

The real feed travel l _{f [ea} i (t) can be defined as a change in the distance between the surface of the abrasive body and the axis of rotation of the workpiece

from the time of the gate to the considered time t, based on the contact point grinding body / workpiece, be understood.

The signal of the measuring controller corresponds theoretically in a first approximation to the (mirrored on the abscissa) real Feed path, whereby due to the diameter measurement cer factor 2 added. A small deviation by the amount

of the feed s, = Vf _r "| / n _w results from the offset of the buttons by -90 ° or -270 ° compared to the contact point

Abrasive / workpiece. Due to various causes (vibrations, abrasive grains or grinding chips between the buttons of the Measuring control device and the workpiece surface, shape error of the workpiece surface) has the signal of Measuring control device on a relatively high noise component. The essence of the invention is the optionally filtered, continuous output signal of Measuring control device in the grinding and / or in a Zwischenausfunk phase of a grinding cycle electronically

After an analog-to-digital conversion and storage by a computer with a program on the

Basis of a regression algorithm to process the characteristic T (time constant) to determine which, as above

set out, in connection with the system deformation or cutting ability of the grinding wheel is and thus adaptive

Control of the process sequence during grinding or to estimate the grinding behavior or state of wear of the Abrasive body can be used. The invention will be explained in more detail with reference to an embodiment. Fig. 2 shows a schematic representation of a cylindrical grinding machine with measuring control device and to be processed

Workpiece.

The workpiece is touched by the probes of the measuring control device during processing. According to the structural design of the measuring system can thus the diameter difference to a normal [current Allowance ζ (O) or with an absolute measuring system also the actual diameter can be measured. A corresponding electrical signal is available at the output of the electronics for processing the analog signals Available. The exemplary embodiment relates to a grinding cycle roughing intermediate sparking-finishing Spark-out. (Fig.3) At the beginning of the Sc! .leifzyklus the grinding headstock with increased feed rate on the Workpiece moved. After the cut of the grinding body on the workpiece, the on the detection of a suitable characteristic (eg structure-borne noise

or diameter change) can be detected, is carried out immediately or after a short stoppage of

Feed drive switched to rough feed rate. Upon reaching a predetermined allowance for Zwischenausfunken the feed drive is stopped. At the same time, the computer integrated into the measuring control device receives a signal for taking over measured values. For this purpose, the electrical output signal of the electronics of the measuring control device corresponding to each still

existing oversize ζ (t), possibly after a low-pass filtering, during the Zwischenausfunk phase at short intervals (At = 0.01 ... 0.05 s) sampled and stored after analog-to-digital conversion. This is the discrete values Z | = z (i · At), (i = 0; 1; 2; ...; k). The measured value acquisition can extend over the entire intercommunication phase.

The finishing feed speed should then be switched on if the real feed rate is the same

given nominal value.

One possible criterion for completing the acquisition of the measured value is the condition

SQV

2-m-At "'"

(m> 1; qe {1; 1,5}) (7)

ζ ... allowance

Vu ... Simple feed rate

be specified.

During the finishing phase, the stored measured values are processed. In a first step, the value obtained by discrete measured values Z | given waveform with a fast Regression algorithm approximated by a polynomial of the mth degree (m a 3) (in the example m = 3):

y, = A ₀ + A, * ti + Al X ₁ + A ₃ t? with t | = i · At (i = 0; 1; 2; 3; 4; ...; k) (8)

By differentiation one obtains:

y | = A ₁ + 2 · A ₂ · tj + 3A ₃ · t? (9)

The y! are the input for a second regression calculation

 Based on Eq. (5), the parameter T is calculated by equation (10).

K KK

(K + 1) Σ lny, '- ι, - Σ lny.' Σ t, i = 0 i = 0 i = 0

(10)

On the basis of the parameter T, the system deformation or the spark oversize can be calculated.

z. = 2-f _Q "= 2-r-Vf, rT (11)

i.e. Upon reaching this allowance, the finishing feed speed is switched off and thus the final

Phase out, which is to ensure minimal roughness, low dimensional and dimensional errors introduced. The coefficient r is u. a. depends on the combination of abrasive material coolant and must be experimental

be determined. For materials with a good approximation according to Eq. (2) r = »1.

For the processing of similar workpieces (constant system stiffness Cg ₁₁ ), condition (12) can be a criterion for Assessment of the grinding behavior or to detect the end of life of the grinding wheel (trend monitoring)

be specified.

The currently determined characteristic variable T is in this case obtained with the parameter T ₀ obtained immediately after dressing

compared. When a predetermined tolerance band is exceeded, a dressing signal is output.

TST ₀ ± ρ · Τ _ο (12)

The coefficient ρ is an experimentally determined value. In a modified form, the described method and the measuring device arrangement are also applicable to other grinding cycles (eg. Roughing-finishing sparks) applicable. Likewise, the parameter T can also be determined in the grinding phase, which, however, due to the effects of Initial shape errors only makes sense for pre-ground workpieces.

Claims (2)

1. A method for automatically determining a characteristic for the control of the process sequence when grinding with measuring control device, characterized in that a delay constant corresponding and related to the system deformation characteristic when grinding or Zwischenausfunken exclusively from the continuous output signal of the measuring control device is determined by computer and building on this characteristic is carried out in a multi-stage grinding cycle, the adjustment of the Ausfunk allowance. 2. A method for automatically determining a parameter for controlling the process sequence when grinding with measuring control device, characterized in that this parameter is determined solely by the continuous output of the measuring control computer-aided and this characteristic as a basis for the evaluation (trend monitoring) of the grinding or wear behavior or to detect the end of life of the grinding wheel (dressing time) when machining similar workpieces (constant system stiffness).