Machine tools abstract
A monitoring procedure and a monitoring installation for machine
tools with a motor-driven work spindle and a separate protection
device. The actual mass inertia moment of a tool fitted into the
work spindle is determined by measurement and compared with a mass
inertia moment calculated from the data of the tool. In addition,
a predetermined parameter of a tool fitted into the work spindle
is compared with that of the maximum parameter for the tool which
is dependent on the strength of the protection device. The work
spindle will be driven at the predetermined desired speed of rotation
only if the actual mass inertia moment agrees with the calculated
mass inertia moment and the predetermined parameter is smaller than
or equal to the maximum parameter predetermined by the strength
of the protection device.
Machine tools claims
What is claimed is:
1. A monitoring process for machine tools with a motor-driven work
spindle and a separate protection device, the process comprising:
determining the actual mass inertia moment of a tool fitted into
the work spindle on the basis of a measurement and compared with
a mass inertia moment calculated from predetermined mass inertia
moment of the tool; comparing a predetermined parameter for the
tool fitted into the work spindle with a maximum parameter dependent
on the strength of the protection device for this tool; and activating
the work spindle at the preset reference revolution rate only if
the actual mass inertia moment agrees with the calculated mass inertia
moment and the predetermined parameter is smaller than or equal
to the maximum parameter predetermined by the strength of the protection
device.
2. The monitoring process according to claim 1 wherein the predetermined
parameter of the tool diameter is compared with that of the maximum
diameter predetermined for the programmed speed of rotation.
3. The monitoring process according to claim 1 wherein the predetermined
parameter is the desired speed of rotation of the work spindle which
is compared with a maximum speed of rotation dependent on the tool
diameter.
4. The monitoring process according to one of claims 1 to 3 wherein
in the event of a divergence between the actual mass inertia moment
and the calculated mass inertia moment and/or in the event of the
maximum parameter being exceeded, the drive of the work spindle
is stopped and/or an error message is issued.
5. The monitoring process according to one of claims 1 to 3 wherein
the actual mass inertia moment of the tool fitted into the work
spindle is determined on the basis of the acceleration time measured
during the acceleration of the tool to a predetermined speed of
rotation.
6. The monitoring process according to claim 4 wherein the actual
mass inertia moment of the tool fitted into the work spindle is
determined on the basis of the acceleration time measured during
the acceleration of the tool to a predetermined speed of rotation.
7. The monitoring process according to one of claims 1 to 3 wherein
the actual mass inertia moment of the tool fitted into the work
spindle is determined on the basis of the tool dimensions obtained
by measurement.
8. The monitoring process according to claim 4 wherein the actual
mass inertia moment of the tool fitted into the work spindle is
determined on the basis of the tool dimensions obtained by measurement.
9. The monitoring process according to one of claims 1 to 3 wherein
the work spindle will only be activated to run at the desired speed
of rotation if the measured uptake of current by the spindle drive
during the acceleration of the work spindle to a predetermined reference
rate of rotation lies above a reference curve which results during
the acceleration of a work spindle without a tool fitted.
10. The monitoring process according to claim 4 wherein the work
spindle will only be activated to run at the desired speed of rotation
if the measured uptake of current by the spindle drive during the
acceleration of the work spindle to a predetermined reference rate
of rotation lies above a reference curve which results during the
acceleration of a work spindle without a tool fitted.
11. The monitoring process according to claim 5 wherein the work
spindle will only be activated to run at the desired speed of rotation
if the measured uptake of current by the spindle drive during the
acceleration of the work spindle to a predetermined reference rate
of rotation lies above a reference curve which results during the
acceleration of a work spindle without a tool fitted.
12. The monitoring process according to claim 7 wherein the work
spindle will only be activated to run at the desired speed of rotation
if the measured uptake of current by the spindle drive during the
acceleration of the work spindle to a predetermined reference rate
of rotation lies above a reference curve which results during the
acceleration of a work spindle without a tool fitted.
13. The monitoring procedure according to one of claims 1 to 3
wherein the work spindle will only be driven at the present desired
revolution rate if, during acceleration of the work spindle to a
predetermined reference revolution rate, a measured imbalance lies
under a maximum value of admissible imbalance.
14. The monitoring process according to claim 4 wherein the work
spindle will only be driven at the present desired revolution rate
if, during acceleration of the work spindle to a predetermined reference
revolution rate, a measured imbalance lies under a maximum value
of admissible imbalance.
15. The monitoring process according to claim 5 wherein the work
spindle will only be driven at the present desired revolution rate
if, during acceleration of the work spindle to a predetermined reference
revolution rate, a measured imbalance lies under a maximum value
of admissible imbalance.
16. The monitoring process according to claim 7 wherein the work
spindle will only be driven at the present desired revolution rate
if, during acceleration of the work spindle to a predetermined reference
revolution rate, a measured imbalance lies under a maximum value
of admissible imbalance.
17. The monitoring process according to claim 9 wherein the work
spindle will only be driven at the present desired revolution rate
if, during acceleration of the work spindle to a predetermined reference
revolution rate, a measured imbalance lies under a maximum value
of admissible imbalance.
18. A monitoring installation for machine tools with a motor-driven
work spindle and a separate protection device, the installation
comprising: a device for comparing the mass inertia moment of a
tool fitted into the work spindle determined by measurement, with
the mass inertia moment predetermined data calculated for the tool;
a device for comparing a preset parameter of the tool fitted into
the work spindle with a maximum parameter which is dependent on
the strength of the protection device for the tool; and a device
for the release of a predetermined desired speed of rotation of
the work spindle when the actual mass inertia moment agrees with
the calculated mass inertia moment and the predetermined parameter
is greater than or equal to the maximum parameter predetermined
by the strength of the protection device.
19. The monitoring installation according to claim 18 and further
comprising a device for the determination of a time-related flow
of the current uptake of a drive motor during acceleration to a
predetermined reference speed of rotation.
20. The monitoring installation according to one of claims 18 or
19 and further comprising a device for the determination of an
inadmissible imbalance of a tool fitted into the work spindle.
Machine tools description
BACKGROUND
1. Field of the Invention
The invention concerns a monitoring procedure and a monitoring
installation for numerically-controlled machine tools with a motor-rotated
work spindle and a separating protection device.
2. Discussion of Related Art
For the protection of the operator, numerically controlled machine
tools are as a rule, equipped with partitions or protective booths
which are intended to prevent potential danger to the operator from
flying tools, work or fragments. It is, however, the inspection
windows of such partitions or protective booths which are of a limited
strength. Since protective devices must often be mobile, their thickness
also has limits. Due to incorrect programming or faulty operation
of the machine tools, operating conditions may intervene which can
lead to danger for operators. Thus, for example, a replaceable bezel
of a milling cutter may, in the event of a fracture due to incorrect
programming or incorrect input of the rotational speed, fly away
from the tool holder with such high energy that the separating protection
devices cannot withstand the impact.
SUMMARY OF THE INVENTION
It is a primary purpose of the present invention to provide a monitoring
procedure and a monitoring installation for machine tools which
make possible an improvement in machine safety.
According to the invention, the actual mass inertia moment of a
tool held in the work spindle is determined on the basis of a measurement
and compared with a mass inertia moment calculated from the predetermined
data for the tool in question. In this way it is possible to verify
whether the geometrical tool data entered into the NC control agree
with the data of the tool fitted into the work spindle or whether,
for instance, erroneous diameter values were entered or programmed.
By comparing a predetermined parameter of the fitted tool with the
maximum parameter which depends on the strength of the separating
protective device with the chosen processing data, it is possible
to determine whether the safety device could withstand a possible
collision with flying parts. Rotation of the work spindle will only
take place at the desired speed of rotation, if the actual mass
inertia moment agrees with the calculated mass inertia moment and
the predetermined parameter is smaller than or equal to the predetermined
maximum parameter predetermined by the strength of the protection
device. In this way it is possible to identify an erroneous tool
diameter and speed of rotation entry, and the speed of rotation
of the work spindle can be restricted to an admissible value or
the work spindle can be stopped and an error message issued.
Thus, for example, the predetermined parameter can advantageously
be the entered tool diameter, which is compared with a maximum diameter
dependent on the programmed speed of rotation. The predetermined
parameter can, however, also be the entered desired speed of rotation
of the work spindle, which is compared with a maximum speed of rotation
dependent on the tool diameter.
In the event of a divergence between the actual mass inertia moment
and the calculated mass inertia moment, or if the maximum parameter
is exceeded, or both, it is advantageous to stop the work spindle
drive or for an error message to be issued, or both. The speed of
rotation of the work spindle can also be reduced to an admissible
value.
The actual mass inertia moment of the tool fitted into work spindle
can be calculated particularly easily on the basis of the acceleration
time which is measured during the acceleration of the rotation speed
of the tool to a predetermined reference value. If the machine tool
possesses, for example, a mechanical or an optical system for determining
the measurements of the tool fitted into the work spindle, the actual
mass inertia moment can also be calculated from the tool data determined
as set out above and compared with the mass inertia moment calculated
from the entered values of the mass inertia moment. The actual mass
inertia moment can also be calculated by either method, with a resulting
greater degree of reliability.
In a further advantageous embodiment of the present invention,
the work spindle is first accelerated to the predetermined reference
speed of rotation while the current uptake of the drive motor is
measured. By comparing the current uptake with a reference value
obtained during the acceleration of a work spindle without a tool
fitted, it is possible to verify whether a tool has been fitted
into the work spindle. If this is not the case, the drive can be
stopped and an error message issued.
A further advantageous embodiment is characterized by the fact
that the work spindle will be driven at the predetermined desired
speed of rotation only if an imbalance measured during the acceleration
of the speed of rotation of the work spindle to a predetermined
measured speed of rotation reference value is below a maximum admissible
imbalance.
BRIEF DESCRIPTION OF THE DRAWING
The objects, advantages, and features of the present invention
will be more clearly perceived from the following detailed description,
when read in conjunction with the accompanying drawing, in which:
FIGS. 1 to 4 are functional flow charts which, together, describe
the monitoring procedure according to the invention;
FIG. 5 shows a typical flow of the current by a drive motor during
the acceleration of a work spindle with and without a tool fitted;
and
FIG. 6 is a diagram of the relation between the maximum admissible
tool diameter and the maximum admissible speed of rotation of the
work spindle as a function of the restraint capacity of a separating
protection device.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIGS. 1 to 4 show the individual processes of automatic monitoring
which can, for example, be carried out in the case of a numerically
controlled universal milling and drilling machine with an automatic
tool changing device and a protection booth, both with NC operation
100 and with manually controlled operation 200.
As FIG. 1 shows, NC program input 100 and input 101 of the NC program
take place through direct programming on the machine or through
the entry of an already prepared program into an NC control. At
the same time, storage 102 is carried out of geometrical tool data
of tools located in the tool storage. Following start 103 of the
NC program, a tool change 104 is carried out by means of corresponding
activation of the automatic tool changing device to introduce the
required tool into the work spindle. Equally, in the case of manually
operated operation 200 the geometrical data of the tools located
in the tool storage or manually inserted are stored in the NC control.
By means of a corresponding control command given by the operator,
an automatic tool change 201 takes place and the required tool is
introduced into the work spindle.
After the completion of a tool change which has been initiated
either by means of the NC program or the tool change procedure 104
or 201 by the operator, the work spindle is accelerated to the reference
speed of rotation by step 300. Current uptake by the drive motor
is measured as a time-related function and compared with a reference
curve for the acceleration of the work spindle without a tool fitted,
which is stored in the control of the machine tool.
FIG. 5 shows a typical flow of current during the acceleration
of the working spindle with and without a tool fitted. The lower
curve which appears in FIG. 5 shows current uptake during the acceleration
of the work spindle without a tool fitted. This curve can be stored
in the control as a reference curve. On the other hand, the upper
curve shown in FIG. 5 shows the flow of current during the acceleration
of the working spindle with a tool fitted.
By comparing an actually determined acceleration curve with the
reference curve stored in the control, it is then possible to verify
whether a tool has been fitted into the work spindle.
If, for example, a verification carried out in step 301 according
to FIG. 2 shows that the flow of current measured in step 300 does
not lie within an admissible range above the reference curve, it
is assumed that no tool has been fitted into the work spindle and
the drive of the work spindle is then stopped by step 302 and an
error message is issued. When, however, the measured uptake of current
is within the admissible range, it is assumed by means of a step
303 first assessment that a tool has been fitted into the work spindle.
In a further step 304 the actual mass inertia moment J.sub.1 of
the tool fitted into the work spindle is calculated on the basis
of the value measured during the acceleration of the work spindle.
Using the formula:
it is, for example, possible to calculate the total mass inertia
moment J.sub.ges by means of a measured acceleration time t in the
course of the acceleration of the tool to a predetermined reference
value n at a constant motor moment M.
The total mass inertia moment J.sub.ges consists, in accordance
with the following formula
of the sum of the motor inertia moment J.sub.M, the spindle inertia
moment J.sub.s, the tool inertia moment J.sub.1 and the inertia
moments of the further masses to be accelerated, such as, for example,
the tool tension jack and the like. Therefore it is possible to
calculate the actual inertia moment J.sub.1 of the tool fitted into
the work spindle by means of subtracting the known values of the
motor inertia moment J.sub.M, the spindle inertia moment J.sub.s,
and, so on, from the measured total inertia moment J.sub.ges
In a further step 305 a mass inertia moment J.sub.2 is calculated
from the geometrical data of the tool fitted into the work spindle
which are stored in the NC control and compared in a further step
306 with the mass inertia moment J.sub.1 determined in step 304.
If the mass inertia moments J.sub.1 and J.sub.2 differ from one
another, then the drive of the work spindle is stopped by step 302
and an error message issued.
If the mass inertia moments J.sub.1 and J.sub.2 agree with one
another, then, as is shown in FIG. 3 the imbalance of the tool
which is fitted into the work spindle is verified in step 307 which
follows. This can be carried out by means of a knock sensor of the
type used in motor vehicles. When the measured imbalance exceeds
a maximum admissible value, the work spindle is stopped in the next
step 308 and an error message is issued. If, however, the measured
imbalance lies within the admissible range, the verification continues.
In the case of machine tools which posses a separate installation
for the mechanical or optical mensuration of tools, an additional
further safety verification can be carried out. In the course of
this procedure, a mass inertia moment J.sub.3 is calculated in step
310 from the tool data determined by the mensuration 309 of the
data and compared, in a further step 311 with the mass inertia
moment J.sub.2 which had been calculated in step 305 from the tool
data stored in the NC control. In the event of a divergence between
the respective mass inertia moments J.sub.2 and J.sub.3 the work
spindle is stopped by step 308 and an error message is issued.
If the mass inertia moments J.sub.2 and J.sub.3 agree with one
another, then, as is shown in FIG. 4 in a next step 312 the maximum
admissible diameter d.sub.max of the tool from the restraint capacity
or restraint energy E.sub.ruck of the protection booth is calculated
as a function of the rate of rotation, it being assumed that the
protection booth can absorb a certain amount of energy without fracturing.
This energy can be determined by means of shot trials using a predetermined
projectile.
Thus, for example, inspection windows of 12-mm thick polycarbonate
sheet can absorb a dose of energy of some 1100 Nm. If a loss of
strength resulting from the aging of the material is taken into
account, a maximum restraint energy of 500 Nm can be assumed for
polycarbonate sheet. This maximum restraint energy yields the following
formula for the calculation of the relationship between the tool
diameter and the revolution rate n of the work spindle.
Assuming that the mass m of a flying part is 0.1 kg, the maximum
admissible tool diameter d.sub.max for the programmed desired speed
of rotation, n.sub.soll can be calculated.
FIG. 6 shows the relationship between the maximum admissible tool
diameter and the maximum speed of rotation of the spindle for different
restraint energies under the action of a standard shot of 0.1 kg.
The maximum diameter d.sub.max calculated in step 312 is compared
in the next step 313 with the measured or stored tool diameter,
or both. When the measured or stored tool diameter exceeds the admissible
maximum, the work spindle is stopped in the next step 314 and an
error message is issued. Otherwise, the programmed speed of rotation
n.sub.soll is released in step 315.
From the immediately preceding relationship, it is however also
possible to determine in the same way a maximum speed of rotation
of the work spindle for a given tool diameter and to compare it
with the programmed speed of rotation.
If the programmed speed of rotation n.sub.soll is released, it
is then possible to verify in a further step 316 whether it is under,
for example, a predetermined limiting value as a result of storage.
If this is the case, the work spindle is activated at the programmed
speed of rotation in step 317. Otherwise, the work spindle is stopped
in step 318 and an error message is issued.
By means of the verification according to the invention, it is
possible to detect an erroneous entry of the tool diameter or the
speed of rotation, or both, and to prevent a resulting potential
danger to the machine operator. |