Note: Descriptions are shown in the official language in which they were submitted.
1~ 37
BACKGROU~D 0~ ~HE INVE~I0~
~he present invention concerns a process for the
contact-free measuremen-t o~ a dimension of at least
one object, wherein a ~ine light beam, more especially
a laser beam, is deflected across the object, within
a measuring field, in the direction o~ the dimension
to be measured, and the period of interruption of the
light beam by the object is compared with a reference
period, and wherein the dimension of the object is
ascertained from these periods.
In a known measuring process of this kind the
period of interruption of the light beam by the
object is compared with the period of the transition
of the light beam across a window de~ining the mea~
~5 suring field (US - PS 4,082,L~63). ~he dimension of
the object -to be determined thus has the same relation-
ship to the dimen.sion of the window opening as -the
period of the in-terruption of the light beam b~ the
: object has to the period of the transition of the
light beam across the measuring field, that is -to
say ~rom window edge to window edge. Errors which
can occur in this method of measurement due to a
non constant velocity of transi-tion of -the light
beam across the measuring field are compensa-ted b-~
providing a coarse grid in the measuring field during
the manufacture of the measuring app æ atus, b~ means
, ~
~61~437
-- 3 ~
of which calibration values can be stored. An inter-
polation is necess æy to obtain measurement values
between the calibration values. ~his known measuring
process of~ers only limited possibilities ~or the
determination and processing of measuremen-t values,
because data can be collected and processed only at
each transition o~ the light beam through predeter-
mined points. ~he time available ~or the processing
of data is correspondingly short. As stated only a
rela-tivel~ coarse calibration is possible ~or which
a special program unit is necessary, which is such
that a recalibra-tion o~ an installed apparatus during
servicing is very di~icult. ~he comparison o~ the
dimension to be measured with the dimension o~ a window
opening re~uires that this window opening be very
accurately measured and does not alter, a condition
which is dif~icult to maintain, ~or example, with
variations in temperature.
SUMMARY 0~ ~E INVE~I0~
It is the object o~ the present invention -to
provide a versatile measuring process which has a min-
imum o~ sources o~ error.
~he invention accordingl~ provides a process for
measuring a dimension o~ a-t least one object without
physicall~ contacting said objec-t, wherein a fine
37
~_ 4 _
light beam is deflected across the object in the direc-
tion of the dimension to be measured, The instants at
which the light beam is blocked and unblocked by the
object are recorded and stored as measurement data.
The measurement data are evaluated to provide a measure
of the dimension by comparison of the period of time
defined between the recorded instants with a predeter-
mined reference period of time related to the speed of
deflection of the light beam. In accordance with the
invention, the instants recorded during a plurality of
consecutive deflections of the light beam across the
object to be measured are stored as measurement data
and the evaluation of the corresponding measurement
data is effected subsequently and collectively while
new data are detected and stored,
The invention, in accordance with a further
embodiment, provides a process for measuring a dimen
sion of at least one object without physically con-
tacting said object, wherein a fine light beam is def-
lected across the object in the direction of the dimen-
sion to be measured. The instants at which the light
beam is blocked and unblocked by the object are recor-
ded and stored as measurement data, The measurement
data are evaluated to provide a measure of the dimen-
sion by comparison of the period of time defined bet-
ween the recorded instants with a predetermined refer-
ence period of time related to the speed of deflection
of the light beam, In accordance with the invention,
there is provided memory means. The process includes
storing in the memory means at time addresses position
values corresponding each to one predetermined position
of the light beam during its deflection, The values
are detected from the memories at the instants at which
the light beam is blocked and unblocked by the object.
The process also includes the further step of detecting
reference time data and evaluating the dimension and/or
position of the object from the position values.
,~.,
.... . . ..
37
a -
In accordance with a still further embodiment
of the invention, there is provided a process for mea-
suring a dimension and/or position of at least one
object without physically contacting the object. A
fine light beam is deflected across the object in the
direction of the dimension to be measured, and the
instants at which the light beam is blocked and unblocked
by the object are recorded and stored as measurement data.
The measurement data are evaluated to provide a measure
of the dimension by comparison of the period of time
defined between the recorded instants with a predeter-
mined reference period of time related to the speed of
deflection of the light beam. In accordance with the
invention, there is provided the improvement comprising
deflecting the light beam across an optical window having
edges defining an instant of entering of the light beam
into the window and an instant of the light beam leaving
the window. The object is placed in the window, and a
periodicity of scanning cycles of the light beam is
detected. There is also included the step of storing
all data indicative of the instants at which the light
beam is blocked and unblocked by the object and by the
window respectively and indicative of the scanning cycles.
Calibrated data is stored in accordance with alinearities
of the scanning movement of the light beam through the
window, and the dimension and/or position of the object
is selectively evaluated from the data.
From a different aspect, and in accordance with
the invention, there is provided a device for the contact
free measurement of a dimension of at least one object.
The device includes a light source for providing a fine
light beam, and means for deflecting the light beam
across an object to be measured in the direction of the
dimension which is to be measured. Means are provided
for determining the instants of time at which the light
beam respectively impinges upon and moves off the object.
,
437
- 4b -
Means are also provided for dynamically storing measure-
ment data corresponding respectively to the instants of
time, and means are further provided for calculating
from the meas~rement data and from a reference value
corresponding to the rate of deflection of the light
beam the value of the dimension. This value is deter-
mined in accordance with the time differences between
the instants of time, MeanS are provided for displaying
the resulting measurement value, the calculating means
having a computer-controlled system including a central
processor unit. A first memory is provided for receiving
the measurement data during each of a plurality of con-
secutive measurement cycles, and a second memory is pro-
vided for receiving data from the first memory~ The
arrangement is such that between each two consecutive
measurement cycles the system operates in the direct
memory access mode to transfer data from the first memory
to the second memory, and that during each measurement
cycle the data contained in the second memory is pro-
cessed by the central processor unit whilst the data in
the first memory is being updated.
BRIEF DESCRIPTION OF IHE DRAWINGS
Figure 1 is a diagrammatic view of a measuring
.
3~7
-- 5 --
device,
~igure 2 is a circuit diagram of the device
shown in Figure 1,
~igure 3 is a diagram illustrating waveforms
occurring in the circuit o~ ~igure 2, and
~igure ~ is a diagram explaining the measure-
ment of a transparent object.
DESCRIPIION 0~ ~HE PRE~ERRED EMBODIMEN~
~he device according to ~igure 1 comprises an
optical s~stem which partly consists of known ele-
ments. A fine laser beam 2 is directed from a dia-
grammatically illustra-ted source 1 onto an octagonal
mirror 3 driven at a constant rotary speed. ~he re-
flected laser beam passes through an objective com-
prising a lens 5 and thence passes across a measuring
field which is defined by a shutter or a window with
boundaries 6. ~he optical system is so arranged that,
be~ond the lens 5, the ligh-t beam constantly extends
parallel to the optical axis, and is moved from the
upper to the lower edge of the window 6-6 as the
mirror 3 rotates in the clockwise direction indicated
by the arrow in Figure 1. Each facet of the mirror
3 causes one transition of the light beam across the
window to effect a corresponding measurement.
In the illustrated example an object 8 to be
measured is arranged in the measuring region, and may,
for example, be a cable, a wire, a pipe or the like,
which runs transversely to the optical axis of the
measuring device and o:~ which the outer diameter is
to be determined. Beyond the measuring position there
is arranged a condenser lens 9 which focuses the laser
beam onto a photocell 10. ~he photocell produces an
output signal ~ as shown in Figure 3, which is 0 or
low when the beam is screened by the window elements
6 or by -the object 8 and which is I or high when the
laser beam is unobstructed. As shown in Figure 3,
two impulses occur periodically, the impulses begin-
ning with the entry of the light beam into the window
6-6 and ending with its exit therefrom, and the gap
between the two impulses corresponding to the screen-
ing of the beam by the object 8. ~he embodiment o~
Figures 1 and 2 comprises a digital evalua-tion circuit
with a microprocessor. A single photocell 22 is ar-
ranged on one side o~ the window 6-6, namely the side
~rom which the ligh-t beam enters the window.
As shown in Figure 2 the microprocessor 23 is
connected by way of a data bus 24 and an address bus
25 with further circuit parts.
~he input signal ~ from the photocell 10 is
applied to a logic circuit 36 incorporating a dif~er-
entiator which responds to the rising and falling
~168~37
flanks of impulses of -the input signal, an address
counter control arrangement and further control cir-
cuits. A signal from a transmitter 3" is also fed
to this logic circuit, said signal being produced
by a chopper rotating with the mirror 3 and consist-
ing of a too-thed disc 3' with 8 -teeth corresponding
to the 8 faces of the mirror. The output of an os-
cillator 30 is continuously applied to a counter 29
which is thus cons-tan-tly incremented, and -the output
of the counter is applied to a memory 27 by way of
a buffer latch 28. The oscillator operates, for
example, at a frequency of 18 MHz and the counter
29 has a high counting capacity of, for example, 24
bits. The transfer of the output from the counter
to the memory 27 is con-trolled by the logic circuit
36 in a manner to be described below. The circuit
further comprises an address counter 35 which is
connected to the memory 27 and, by way of circuits
37 and 38, wi-th the data bus 24 and the address bus
` 20 25.
A permanent read-only memory 31 defines the
progr~m rou-tine and also serves for the storage of
correcting data at defined addresses. A dynamic
memo~y 32 serves the processor as a working memory
for all data -to be processed. An input-output unit
33 applies the measurement values to a display 34.
.
:~16~437
-- 8 --
~ he control of -the memo~y 32 is effected by way
of an OR gate 39 either in the direc-t memory access
mode by way of the logic circuit 36 or during the pro-
cessing of measurement values by the microprocessor
(CPU) 23.
~igure 3 shows the inpu-t signals, namely the
measurement signal E, which, at the instant No eorres
ponding to the entry of the ligh-t beam into the window
6, changes from O to I, -then, during a first transition
of the light beam across -the objeet 8 corresponding
to the period P1, returns to 0, and again changes to
I, when the light beam illuminates the photocell 10
in its transition between the object 8 and the exit
from the window 6. A plurality of measurement periods
are repea-ted in this manner, eight sueh measurement
periods producing the measurement impulses P1 to P8
and corresponding to one measurement cycle or one
re~olution of the mirror 3. ~igure 3 also shows the
signal C of the chopper as well as a signal C' trans-
mit-ted from the logic circuit 36 to the microprocessor
(CPU) 23 and formed by di~iding the chopper signal
by the factor of eight. At each occurrence of an
impulse flank in the signal E, corresponding to each
blocking or unblocking of the light beam, the instan-
taneous coun-t of the counter 29 is stored in the memory
27 and remains a~ailable there as a measuring value.
~hortly after the occurrence of the flank C" after
each cycle of eight measurements, the microprocessor
is interrup-ted and the circuit continues to operate
in the DMA (direct memory access) mode. All of the
values in the memory 27 are thus transferred to the
memory 32. When this transfer is complete, the logie
circuit is switched to the measurement mode and the
microprocessor 23 is caused to run the program. ~ince
the DMA~logic has direct access to both memories 27 and
32, the -transfer of the values can be effected in a
ma-tter of mil]iseconds, and in the present embodiment
i-t can be effected in the time space between -two con-
secu-tive measurement cycles, as illustrated in ~igure
3. As the new measuring cycle begins, and new data
is read in-to the memory 23, the evaluation of the
previously recorded data, in aeeordance with the pro-
gram contained in the memory 31, is effected as a
separate opera-tion, and the result is then indicated
on the display by way of the output circuit 33.
~he program can be changed, and can thus be
adapted -to desired re~uiremen-ts, for example to enable
the measurement of a plurality of objects located in
the measuring field, in which case the evaluation
can easily be so programmed that one or more time
spans or periods can be ascertained, during which
the light beam is screened by a corresponding object,
and the dimension of the or each of these objects
8~37
- 10 -
is ascertained in the previously described manner
by comp æison of each period, or of a sum of the
periods, with the period of the measurement cycle.
Figure 4 shows a possibility for the measure-
men-t of cylindrical, transparent objec-ts, for exam-
ple plastics tubes for surgical purposes. ~he signal
E comprises the rising flank No upon entry of the
light beam into -the window 6, as already described.
When the ligh-t beam impinges upon the transparent
object total reflection of the light beam occurs
so that ligh-t no longer reaches the photocell 10
and a firs-t falling flank N1 occurs in the signal.
Especially with hollow objects, several phases of
transmission and reflection of light then occur,
which result in the occurrence of a corresponding
plurality of signal flanks. At the instant Nx the
ligh-t beam moves off the object. A special circuit
in the logic elemen-t 36 is effective to ensure that
the data for the instants No and N1 alike are trans-
ferred to the memory 27. ~he data for the following
instants N2 to N(x-1? only reach the buffer latch 28
and are constantly updated in the buffer. ~hat is to
say that only the data from the last occurring in-
stant is stored. Upon the occurrence of the ~alling
flank of the chopper signal the last value which has
been read into the buffer 28, which corresponds to
' .
the instant ~x, is transferred to the store 27 and
remains available -there for fur-ther processing.
In the preceding case it is assumed -that one
measurement is e~fected during each measurement cycle,
tha-t is to say that the dimension of the object to
be ascertained can be derived ~rom the following
periods:
D = K . P1 + P2 + ... P8
No' - ~o
in other words the desired dimension D of the object
can be derived from the relationship between the sum
of the periods of transition of the light beam across
the object and the period of one rotation of the mirror
. A mean value of eight individual measurements can
also be established. lhus the measurement is indepen-
dent both of the rotary speed of the mirror and of
any variation in its ro-tary speed, and any lack of
geometrical accuracy of the mirror is of no effeet,
since a plurality of individual measurements are
averaged. ~he continuous determination of individual
measurement values can be achieved, however, as well
as any other evaluation or additional mode of opera-
tion, by means of the microprocessor program. Single
measuremen-ts can be ascer-tained and evaluated indi-
vidually. ~t is thus possible to ascertain the dif-
ference between a maximum and a minimum meas~remen-t
37
value and to eliminate a measurement when this in-
creases the maximum value or reduces the minimum
value by, for example, more than 10%. Measurements
which ha~e been de-termined during a cycle of measure-
ment can furthermore be eliminated when the number of
flanks occurring in the signal ~ during the cycle is
not a whole multiple of eight. A counter may be
provided to register each measurement rejected as
invalid as well as each valid measuremen-t and -there-
by to allow a diagnosis of the measuring device. It
is further possible to effect a linearisa-tion in a
simple manner. If the lens 5 is not corrected in
such a manner that wi-th a constant rotary speed o~
the mirror 3 a constant velocity of transition of the
ligh-t beam -through the measurement field between the
edges of the window 6 is ef~ected, then a correction
or calibration is necessary. ~his calibra-tion can
be effected in a manner such that there are coord-
inated to all measurement values which exist in the
memory 27 in the form of counted impulses of the
oscillator 30, corresponding corrected values which
are contained in a special memory. ~he provision of
these coordinated counts or calibration values can
be effected in various ways. lThe impulse counts cor-
responding to various posi-tions within the measuring
field can be determined experimentally and stored.
~ ~L6~3437
_ 13 -
Preferably however a calibration or correction is
effected on the basis of a known mathematical corres-
pondence between the angle of incidence of the light
beam on the lens 5 and the distance of the light beam
within the measuring field from the optical a~is. For
a given op-tical system and a given deflection mirror
there exists a given mathematical function which can
be taken into a consideration. For similar lenses,
to which the same function basically corresponds,
only one valuation is necessary -through the input of
characteristic values or constants K to -take into
considera-tion the curvature of the function or the
variation from a linear course. According to this
mathematical relationship a calibration memory can be
set up, or a calculating program can be effected by
the microprocessor which continuously converts the
determined measurement value in accordance with the
mathematical relationship. ~his kind of calibra-tion
or correction on the basis of mathematical relation-
ship can also be matched to existing apparatus in a
simple manner during servicing. If, for example, an
optical system has to be changed, the corresponding
characteristic values can be fed in. In the case of
the initially described, known arrangement with a
calibration grid, a suitable calibration logic is
necessary which is not integrated into the measuring
116~4~7
apparatus and makes ver~ much more di~ficult a cali-
bration outside the factory.
