Non-contact envelope counter using distance measurement

A counter for counting objects in a stack employs a beam moved by a scan carriage along an edge of the stack. A detector on the carriage determines the position of the portion of the beam reflected by the stack and determines, by optical triangulation techniques, the distance between the source of the beam and the edge of the stack. The resulting signal is used to recognize the presence of objects in the stack and to count them on the basis of this recognition.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to non-contact counters for counting the number of 
objects in a stack. The invention has particular utility for counting 
relatively irregular stacked objects, such as stuffed mailing envelopes 
2. Description of Related Developments 
Bulk mailing operations require highly accurate accounting of objects being 
mailed for job control and billing purposes. Such counts are especially 
important when mailing credit cards because of the need to maintain 
security against unauthorized use of such cards In a typical mailing 
operation for credit cards, several thousand cards per day are mailed as 
replacements to existing customers or new cards to new customers At such 
volumes, manual counting of the cards is expensive and unreliable. To 
accomplish fast and accurate counting of credit cards, highly accurate 
card counters have been developed. In general, these counters scan one of 
the edges of a stack of cards and count them by sensing momentary 
differences in reflected light intensity between the card edges and the 
space between cards. U.S. Pat. Nos. 27,869, 3,790,759, 3,813,523, 
4,373,135, 4,771,443 and 4,912,317 disclose such card counters While such 
systems provide fast and accurate counting of stacks of credit cards, that 
have well defined, substantially uniform edges which can be arranged in a 
highly regular, coplanar fashion, such systems do not provide a means for 
counting irregularly shaped objects, such as stuffed envelopes. Thus, in a 
typical credit card bulk mailing process, a cost effective machine 
counting of the cards can be maintained only up until the point that the 
cards are loaded or stuffed into envelopes. Thereafter, accountability for 
the cards by counting of the loaded envelopes becomes a much slower, more 
expensive, and more unreliable part of the accountability system. This is 
so because the loaded envelopes are irregular in shape and do not present 
a uniform, substantially planar edge array that yields a signal of 
sufficient quality to be used for counting purposes. 
One system for counting stacks of bound booklets is illustrated in Japanese 
Published Patent Application 61-272892. In this design, to improve the 
accuracy of the count, a vibrating stacker is used for aligning up the 
booklets on a booklet stand prior to counting. Such an arrangement 
involves expense in the design and control of the vibrating stand and 
unnecessary delays in counting. Moreover, booklets are of substantially 
uniform thickness and can give a relatively uniform signal response to 
detection. Such as system is less useful for counting a stack of envelopes 
of varying thickness, for example, ones that contain differing numbers of 
credit cards. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide a counter for the non-contact 
counting of objects. 
It is a further object of this invention to provide a non-contact counter 
that accurately counts irregularly shaped objects at high speed. 
It is further an object of the invention to provide a counter for counting 
envelopes, particularly envelopes that have been stuffed and are ready for 
mailing. 
These and other objects of the invention are achieved by an apparatus and 
method wherein a stack of objects, such as envelopes, are arranged with 
commonly aligned edges to present an edge array. The edge array is scanned 
by a radiant energy source and, during scanning, the distance between the 
radiant energy source and the surface of the edge array is measured. Such 
measurement can be carried out by optical triangulation techniques. On the 
basis of such distance measurement, the presence of an object in the stack 
can be determined.

DESCRIPTION OF PREFERRED EMBODIMENTS 
The following description of the invention is in the context of a counter 
for counting envelopes. However, the invention can be utilized for 
counting other stacked objects, particularly objects of varying shape, 
size and edge configurations. 
Referring to FIG. 1, the counter 10 includes a housing 12 having a sloping 
front face 14. The front face 14 includes an elongate scanning slot 16 
extending in the longitudinal direction of the front face 14. 
A scanning carriage 18 is mounted within the housing 12 for movement along 
and beneath the scanning slot 16. The carriage 18 is mounted in a manner 
to provide accurate and substantially unvarying location of the distance 
between the face of the carriage and the slot 16. For example, a pair of 
V-shaped rails (not shown) flanking the edges of the slot 16 may be 
utilized for accurately positioning the carriage. Referring to FIG. 2, the 
carriage 18 is moved alternately in the directions of the solid arrow by a 
suitable drive system (not shown) along the slot 16. The carriage 18 
includes a radiation source window 20 and a radiation detector window 22, 
described in more detail below. 
The counter 10 includes a stacking or aligning member 24 that is pivoted by 
suitable means, such as one of two track rods 29, along the bottom edge of 
the front face 14. The aligning member 24 includes a first aligning 
surface 25a and a second aligning surface 25b and a pair of upstanding, 
opposed end plates 26a, 26b. The aligning member 24 also includes a 
movable plate 28 mounted on a pair of track rods 29. A suitable securing 
means, such as a friction clamp (not shown) is mounted on the plate 28 and 
provides for locking the plate 28 at any desired position along the track 
rods 29. The aligning member 24 is positionable in one of two alternate 
positions, the first being as shown in FIG. 1 wherein the aligning member 
24 rests against the front surface 14 with the aligning surfaces 25a and 
25b each disposed on opposed sides of the scanning slot 16. In a second 
position, the aligning member is pivoted away from the front face 14 and 
extends in a substantially horizontally fashion from the housing 12. The 
stacking member 28 holds objects, such as envelopes, in a stacked 
condition to be counted by the counter 10. 
The counter 10 includes a visual display 30 for displaying a count and a 
control panel 32, which includes manually actuable switches for 
controlling operation of the counter. 
FIG. 2 shows a plurality of envelopes E forming a horizontally extending 
stack of envelopes. The envelopes E are stacked edgewise along the 
surfaces 25a and 25b and are maintained in a substantially vertical 
condition between end plate 26a and movable plate 28 (shown in FIG. 1). 
Thus the envelopes present an edge array extending along the aligning 
member 24. 
As illustrated in FIGS. 2 and 3, the scanning carriage 18 moves beneath the 
edge array of envelopes E. Mounted on the carriage 18 is an optical 
distance measuring system. The system includes a semi-conductor laser 34 
that projects a beam of radiation through the lens or window 20 onto the 
edge array of envelopes E. An optical triangulation measurement system 
measures the distance between the laser 34 and the point of impingement of 
the laser beam on the edge array of the stack. For example, assuming the 
scan carriage is moving to the right in FIG. 2, the system measures the 
distance between the laser 34 and the successive points a, b and c on one 
portion of the stack. As shown in FIG. 3, the distance measurement is made 
by optical triangulation techniques. The point of impingement of the beam 
of the laser 34 on the surface of the edge array is imaged by lens 22 onto 
a position sensing device 36. By sensing the location of the imaged point 
of impingement on the position sensor 36, the distance h can be 
determined. For example, as shown in FIG. 3, when the beam is reflected 
from the edge of an envelope at location b, the incident beam on the 
position detector 36 is at b'. As the carriage 18 scans to the position 
coincident with point c in the edge array, the location of the reflected 
beam on the position sensor moves to point c'. This position sensing is 
accomplished by taking a ratio of two output currents I.sub.1 and I.sub.2 
from respective ends of the position sensor 36. Such optical distance 
measuring or ranging systems are commercially available, one preferred 
system being supplied by Aromat Corporation under the tradename MQ Laser 
Analog Sensor. Accordingly, no further explanation of the distance 
measuring system is necessary other than to note that such systems employ 
a very narrow beam width which allows the system to "see" the edge of an 
article, such as an envelope, with high resolution. 
FIG. 4 relates the analog signal S (in idealized form) from the position 
sensor 36 prior to digital conversion to a segment of the edge array of a 
stack of envelopes being scanned. The shape of the signal S closely 
corresponds to the configuration of the edge array, thereby yielding an 
electronic representation of each item in the stack, which can be counted 
by data processing techniques described below. 
As shown in FIG. 5, the two outputs I.sub.1 and I.sub.2 from the position 
detecting element 36 are supplied to a linearizing circuit 38 to provide 
an analog output signal that is proportional to the distance between the 
laser source and the point of reflection on the edge array. The analog 
signal is supplied to an op-amp 40, used as a buffer to separate the 
sensor from the processing electronics. The signal is then supplied to a 
second op-amp 42 that inverts the signal. The inverted analog signal is 
supplied to an A/D converter 44 so that the signal can be processed by a 
digital electronic microprocessor implemented in CPU 46. The CPU 46 
performs the signal processing and counting routines necessary for 
determining a count of the objects being counted and also controls other 
operations of the counter 10, such as initializing, scanning and 
displaying. The CPU provides the count to a subsequent downstream user, 
such as visual display 30. 
Referring to FIGS. 6 and 7, in order to prevent the beam from passing into 
an undetectable range at the end of a scan cycle, the plate 28 includes 
structure for engaging the endmost envelope. This arrangement includes a 
bracket 50 on which is mounted a spacer plate 52 and a blocking plate 54a. 
A pin 53 loosely retains the plate 54a loosely on the spacer 52 so that 
the plate is free to pivot about the pin 53, thus allowing conforming 
engagement with the end most envelope. A similar plate 54b (FIG. 2) is 
mounted in a fixed position at the left hand end of the slot 16 on face 
plate 14, extending inwardly at end plate 26a to engage the first 
envelope. 
Referring to FIG. 8, a first embodiment of an object recognition and 
counting system is illustrated. Upon startup of the system, the processing 
system is initialized in step S1 as the scan of carriage 18 begins. At S2, 
a predetermined number of readings n are clocked into the microprocessor 
from the A/D converter 44 and in step S3 the readings are averaged. The 
number of readings n can vary and is typically about 5. At S4, a 
determination is made if the average of the readings is within a 
predetermined range which establishes that the readings are valid. If an 
affirmative determination is made at S4, processing proceeds to S5. If the 
determination at S4 is negative, processing proceeds to S12 for a 
determination of whether the data gathering process has ended. 
If the determination at S4 is affirmative, a determination is made at S5 if 
the general direction of the slope of the waveform is going down, i.e., is 
negative. If an affirmative determination is made at S5, an inquiry is 
made at S6 whether the direction of the slope is positive. If an 
affirmative determination is made at S6, at S7 a determination is made if 
the positive pattern has continued over a sufficient number of readings to 
indicate a general direction change in the slope. If an affirmative 
determination is made at S7, a count in an accumulator is incremented by 1 
in step S8 and at step S9, a flag is set to indicate the present general 
slope direction. Alternately, S8 can occur after S11, described below. 
A negative determination at step S5 causes the processing to flow to S10 
wherein a determination is made of whether the slope between the present 
reading and the last reading has turned negative. If an affirmative 
determination is made at S10, processing proceeds to S11, in which a 
determination is made as to whether the pattern has continued long enough 
to indicate a general direction change. If an affirmative determination is 
made at S1l, processing proceeds to S9 to set a flag indicating a change 
to a negative slope. At step S9, processing proceeds to point B wherein 
the next subsequent reading is taken. Similarly, negative determinations 
at step S6, S7, S10 and S1l cause processing to resume at B. 
At S12, if an affirmative determination is made that an end to all possible 
data has been achieved, the processing proceeds to step S13 wherein the 
count accumulated at S8 is sent to a further user such as a processor or a 
display. An end of data determination can be made at S12 on the basis, for 
example, of the carriage 18 being at the end of scan position at which a 
plurality of successive out of range readings are detected, indicating 
that the end of the scan path has been reached. 
In this processing arrangement, at step S8, a count of 1 is added to the 
accumulated count, since it is the spaces between envelopes that were 
counted in this routine. 
In FIG. 9, a second embodiment of a counting process implemented in CPU 46 
is shown. This arrangement uses an interrupt process (shown in FIG. 9A) 
which is run at a predetermined frequency, for example 600 Hz, to collect 
data from the position sensor 36 at equal time intervals. This interrupt 
routine is triggered by a system clock (not shown) and includes step S25, 
at which a value is read from the sensor 36 and S26 where the value read 
in S25 is entered into a memory for later processing by the main 
processing routine. 
In the second embodiment, the system is initialized at S15. Processing then 
flows to S16 at which it is determined if envelopes should be counted. If 
the counter is in a count mode, an affirmative determination is made at 
S16 and processing flows to S17 to determine if sufficient data has been 
collected for processing. In this step, the values stored in memory at S26 
are interrogated to determine if a sufficient number of data points have 
been collected for processing. Typically, 15 to 20 data points are 
preferred for processing. If the determination at S17 is negative, the 
interrogation continues until a sufficient number of data points are 
collected in S26. If the determination at S17 is affirmative, processing 
continues to S18. At S18 the data is processed to remove high frequency 
noise. One preferred technique is to use a finite impulse response filter 
to eliminate such high frequency noise. The coefficients for the filter 
are determined on the attributes of the desired output signal such as 
bandwidth, frequency, etc. Techniques for determining such coefficients 
are known and can be determined, for example, by use of the 
McClellan-Parks algorithm. The data signal resulting after processing at 
S18 has high frequency noise substantially eliminated and peaks and 
troughs in the waveform are smoothed. 
At S19, the filtered digital signal resulting from S18 is differentiated to 
determine the points of slope change in the data signal. In a normal 
counting routine, the points of slope change indicate the location of an 
edge of an envelope. After differentiation, the processing flows to S20 
wherein a determination is made of whether the data represents the 
presence of an envelope. At this step, a two or three step interrogation 
is made to determine if the slope of the data signal has changed, if a 
second reading confirms that the slope has changed and, depending upon 
signal characteristics of the detection system, if the data is above a 
minimum threshold level, indicating that an edge of an envelope has been 
detected. If an affirmative determination is made at S20, processing 
proceeds to S21 wherein an envelope is counted and added to an 
accumulating register. 
If the determination at S20 is negative, processing proceeds to S22 to 
determine if data collection is complete, i.e. that the scan cycle has 
ended. If a negative determination is made at S22, processing returns to 
S17 to continue data collection. If an affirmative determination is made 
at S22, processing proceeds to S23 for a determination of the completion 
state of the counting calculations. An affirmative determination at S23 
results in a process flow to S24, wherein the accumulated count is sent to 
a downstream processor or display. In the event a negative determination 
is made at S23, processing flows to S18 to continue processing of 
unprocessed data. 
The second embodiment of counting method has significant advantages over 
the first embodiment because only two data samples are necessary to 
determine a slope change. As a result, the same processing routine can be 
used to count envelopes having wide variations in thickness. In addition, 
because the samples are taken at equal intervals, the signal more closely 
represents the pattern of the envelopes. 
To provide higher accuracy, two distance measuring systems can be mounted 
on carriage 18, each employing its own counting system. The counts of 
systems can be compared at the end of each scan. If the same count is not 
made by each system, remedial action, such as a recount, can be taken. 
Counters made in accordance with the present invention have significant 
advantages resulting from the distance measuring arrangement disclosed. 
High speed, reliable machine counting of variably shaped items, such as 
envelopes, can be accomplished. The distance measuring sensor has an 
improved depth of field over reflectance type arrangements and is less 
susceptible to counting errors resulting from misalignment of items being 
counted. The use of an arrangement that provides a signal proportional to 
the changing distance measured enables simplification of signal processing 
while yielding highly reliable data. The signal has high resolution and is 
more easily detectable, especially in comparison to systems that rely on 
detecting intensity of reflected radiation. 
While the invention has been described with reference to the structures 
disclosed, it is not confined to the details set forth but is intended to 
cover such modifications or changes as may come within the scope of the 
following claims.