Mail thickness measuring apparatus

Abstract: A mail handling machine includes mail thickness measuring apparatus associated with a singulator mechanism for measuring mail thickness as soon as individual mail pieces are separated by the singulator from a stack of mail pieces.

Description: This invention relates to mail thickness measuring apparatus, and in particular to such apparatus for use in high speed mail handling machine. State-of-the-art mailing machines can perform such automatic functions as handling mail of different sizes and thicknesses, envelope sealing, mail weighing, mail stamping, and mail sorting. In developing machines with such functions, capable of processing mail at high speeds of, for example, four or more pieces per second, it becomes important if not essential that the mail thickness is determined as soon as possible after the mail begins its flow sequence. Knowing the thickness early is important because there usually is a relationship between mail thickness and mail weight, i.e., the thicker the mail, the more it weighs. Typically, heavier mail must be processed slower than lighter mail in a high speed processing environment. Hence, the weight of the mail allows the computer which is controlling the machine to slow the transport mechanisms when carrying heavy mail and speed up the transport mechanisms when carrying lighter mail. It is desirable to control transport velocity as a function of mail weight or mail thickness as soon as the mail pieces begin their flow through the machine. Typically, the mail pieces enter the system from a hopper in stacked form, and one of the first actions necessary is to separate an individual piece of mail from the stack. The mechanism for doing this is called a singulator and the action singulating. European Patent Application (EP-A)225288 discloses a machine for monitoring the thickness of items such as mail pieces. In this machine, a linear variable differential transformer (LVDT) device is operatively coupled with a pinch roller mechanism so that variations in thickness which are detected as an object passes through the pinch roller mechanism are converted, by the LVDT device, to electrical signals which may be digitally processed to yield an accurate indication of thickness, and content. Such processed signals are used to control various machine functions in accordance with the thickness or content of the object which has passed through the pinch roller mechanism. German Patent Application (DE-A)3035744 describes a position encoder which could employ optical markings and photoelectric sensors or Hall-effect sensors or reed switches. The encoder is used for determining the position of machine parts. In U.S. Patent No. (US-A)3035695 there is described a roller which separates articles such as mail pieces (letters) from one another. The roller is rotated so that its working surface is moving in a direction opposed to the direction of conveyance of the mail pieces. Letters are transported by a suction belt. Mail thickness sensors in some prior art machines would typically position on top of the mail piece a follower connected to an optical system involving a light source scanning across an array of light detectors, the position of the light source being determined by the position of the follower, and the position of the light source determining which detector is activated. Mechanical systems have also been used. These prior art systems suffer from one or more of the following shortcomings. With optical systems, frequent maintenance is necessary to keep the optics clean. A mailing machine processing thousands of pieces of mail daily does not provide a clean environment for optical sensors. The signal output frequently was analog. This meant the use of an A/D converter to translate the analog signal into a digital signal that the computer can process, which increased costs. Accuracy of thickness measurement was not always optimal. Especially with high speed processing, it is important to be able to measure the mail thickness in the range of about 0.1 to 19 mm. (0.004 to 0.75 inches) to an accuracy of about 00.05 inches, 1.27 mm. In accordance with the present invention, there is provided apparatus for processing mail pieces comprising means for supplying multiple mail pieces, a singulator for separating individual mail pieces, means for transporting mail pieces from the supplying means to the singulator, and means operatively connected to the singulator for measuring the thickness of mail pieces singulated thereby, characterised by means downstream of the singulator for further processing of the mail and for transporting the single mail pieces to the further processing means, and means for varying the velocity of the further transporting means in accordance with the measured thickness of each mail piece processed. There is particularly described herein a relatively simple but accurate thickness measurement system, for use in mail processing, which outputs an absolute encoded digital value which can be directly processed by a computer to control the velocity of the measured mail piece as it flows through the machine for subsequent sealing, weighing, stamping, and sorting if desired. In a preferred embodiment, connected to a follower which contacts the mail piece top is a permanent magnet having plural poled segments, the magnet position tracking that of the follower. The magnet traverses an array of magnetic field detectors which respond to selected detected magnetic fields, and in response generates an output which is an absolute Gray encoded binary number which is unique for each subrange of mail thickness. Twenty accurate thickness measurements can be made over a range of substantially 0.1 to 25.4 mm (0.004-1.0 inches) to an accuracy of about 1.27 mm (0.05 inches approx). The resultant binary number can then be used to index into a lookup table for selecting an appropriate flow velocity sequence or profile for the measured mail piece in its subsequent processing through an automatic mail handling machine. The invention will now be described in greater detail with respect to several exemplary embodiments in connection with the accompanying drawings, wherein: Fig. 1 is a schematic view of one form of magnetic sensor suitable for measuring mail thickness in accordance with the invention; Fig. 2 is a table showing the binary coded and hex output for the sensor of Fig. 1; Fig. 3 is a front schematic view of a typical mail handling machine employing the sensor of Fig. 1; Fig. 4 is a detailed side view of the singulator and magnetic sensor schematically depicted in Fig. 3. In the several figures, the same reference numerals are employed to designate similar elements. A suitable mail thickness sensor suitable for use in a mail-handling machine, in an embodiment preferred for measuring mail or letter thickness, is schematically illustrated in Fig. 1 and will be briefly described below. The sensor assembly companies a fixed detector assembly 8, and a moving magnet 20. The fixed detector assembly comprises seven Hall effect detectors 10-16 arranged in a row spaced apart by a fixed center-to-center spacing 18. Each detector has an active detecting area indicated by reference numeral 27. The magnet 20 moves in a straight line parallel to the detector row separated by a gap 19. The preferred magnetic array comprises two South (S) poles 22,24 separated by a North (N) pole 23. Additional N poles can be provided at the leading edge, pole 21, and at the trailing-edge, pole 25, of the assembly to sharpen the field transitions. The magnet is moved by the mail piece follower in the direction indicated by the arrow. The position of the magnet 20 shown in solid lines is the start or zero thickness position. In dashed lines are shown magnet positions 20′ and 20″ in which the magnet would have been moved four and nine units, respectively, to the right of its starting position. For the preferred geometry shown, with the active detector area 27 equal to 1.27 mm, 0.05 ins, the detector spacing 18 equal to 0.2 inches (in the arrow direction), S pole 22 .025 inches long, N pole 23 0.1 inches long, and S pole 24 0.15 inches long, the detector array will output twenty different absolute Gray codes over a mail thickness range of 0.1 to 25.4 mm with a worst case resolution of ± about 1.27 mm. The output binary code can be stored in a register 7, and subsequently retrieved by a computer to be processed. Fig. 2 is a table showing the output from each detector in response to positions of the magnet 20. Basically, the detector outputs a "0" when opposite a S pole, and a "1" when opposite no field or a N pole. The column on the right, the Hex equivalent of the adjacent binary coded output, shows that the output is absolute, meaning no two codes are alike. The binary outputs demonstrate Gray encoding, since no more than one bit changes for adjacent magnet positions. The magnet is readily manufactured in the geometry shown, and the detectors are commercially available as inexpensive Hall-effect detectors. The gap spacing 19 would be typically 0.04 inches. As previously mentioned, since the moving part of the sensor is a magnet, and the fixed part the Hall-effect detectors, a rugged sensor is obtained that will withstand much abuse. Since magnetic fields are sensed, the system is virtually immune to dirt and contamination. The direct output of a binary-coded number eliminates the need for analog-to-digital conversion and reduces costs. The Gray encoding ensures high resolution, reliable measurements. In a practical embodiment, the detectors 10-16 are mounted in a common holder or on a common support, with a seven wire connector 6 for the output to the register 7. Fig. 3 illustrates schematically the front end of the mail handling machine, comprising a hopper 30 for receiving a stack of mail pieces 31 for processing. A transport system comprising motor driven rollers 32 and a belt 33 picks out one or more of the mail pieces 31 from the stack bottom and immediately carries them under a singulator mechanism 35 which functions to ensure that only a single piece of mail will thereafter be processed at a time by the machine. The singulator 35 may comprise any one of a number of known mechanisms, provided that it includes a movable element that follows the mail piece top. A preferred singulator comprises a four-bar linkage mechanism 36 which is pivoted on the machine frame. A more detailed illustration is shown in Fig. 4. The forward drive for the mail pieces, shown at 50, is supplied by the belt or belts 32 which is mounted on the machine deck 37. The four-bar linkage 36 comprises one or more reversely-driven belts 38 rotating around pulleys 39 located at the corners of a rhombus formed by the linkages 40. The rhombus is anchored at pulley shafts 44 for pivotable movement on a support 41 extending up from the machine frame. A compression spring 45 biases the singulator 36 downward and applies a load onto the mail which it is helping to singulate. The reversely-driven belts 38 are typically interdigitated with the forward driving belts 32. In operation, if more than one mail piece or overlapped mail pieces enter the zone between the reversely-driven belts 38 and the forwardly-driven belts 32, while the bottom mail pieces is driven forward to the right, any overlapping mail pieces are driven backward. In this process, the bottom mail piece is driven under the singulator nip, the lowermost portion of the reversely-driven belts 38, causing an upwards push on the mechanism. The rhombus 36 deforms to allow mail pieces of varying thickness to pass under it while maintaining its outer circumference. Thus, the rhombus 36 acts as a follower that moves upward in the direction indicated by arrow 43 a distance proportional to the mail thickness. The magnet array 20 depicted in Fig. 1, which is fixed by plate 46 to the lower linkage bar 40, likewise moves upward the same proportional distance. The Hall-effect detector array 8 for the magnet array 20 is mounted on a printed circuit board, which in turn is mounted on the fixed support 41. An optical sensor 47 is mounted in the deck 37 and functions to detect the leading edge of the mail piece. When detected, the sensor shuts down the forward and reverse drives for an instant. Thus, the singulator upward motion stops. At that point, the detector output to the register 7 stabilizes, and the computer, shown at 51, also signalled by the sensor 47, polls the register 7, retrieves the binary coded number stored therein, and in turn stores it in an internal register. After a fixed time delay, typically 20 ms, the drive mechanisms are restarted and the mail piece is carried forward, to the right, and is captured by a takeaway nip formed by driven roller 48 and spring-biased idler 49, affixed to shaft 45, and is thus carried downstream for further processing. If desired, a second sensor (not shown) can be positioned downstream of the sensor 47 which would operate similarly, i.e., detect the leading envelope edge, stop the drives, and then restart them, all under computer control. This would allow a second mail thickness measurement to be made of the same mail piece, and the second measurement averaged with the first to ensure that unevenly stuffed envelopes do not produce an erroneous weight indication. As will be noted from the foregoing description, by associating the thickness measuring sensor with a singulator mechanism that follows mail pieces of varying thickness, the thickness measurement is taken nearly simultaneously with the singulating action, and thus early on in the mail handling process. Thus, the computer is informed of the mail thickness and thus approximate weight at virtually the same time that each mail piece begins its serial processing through the machine. The use of the magnetic field operating sensors ensures trouble free reliable operation even in the environment of high mail throughput machines. Moreover, obtaining a binary coded output directly reduces costs, and when the output is Gray encoded increases accuracy. The mechanism described, as illustrated in the drawings, provides accuracy to 1.27 mm, 0.05 ins of the mail thickness. The resolution and range of measurable thicknesses can be varied by adjusting the geometry of the detector array and magnetic configuration or through the use of linkages between the singulator and the magnet. It will be seen that the preferred embodiment provides a mail thickness measuring apparatus capable of measuring the thickness of mail pieces being processed at high speeds; and also provides a mail handling machine for processing mail pieces of different thicknesses at high speeds wherein the thickness measurement is carried out accurately and early in the mail flow, and while the mail piece is being processed at high speed.

Claims: Apparatus for processing mail pieces comprising means (30) for supplying multiple mail pieces, a singulator (35) for separating individual mail pieces, means (32) for transporting mail pieces from the supplying means to the singulator, and means (8,20) operatively connected to the singulator for measuring the thickness of mail pieces singulated thereby, characterised by means (48,49) downstream of the singulator (35) for transporting the single mail pieces to further processing, and means for varying the velocity of the transporting means (48,49) downstream of the singulator (35) in accordance with the measured thickness of each mail piece processed. Apparatus as set forth in claim 1 wherein the singulator (35) comprises a movable member (38) for contacting the surface of a mail piece and means (36) for mounting the singulator (35) for movement in a direction transverse to the mail piece movement direction in response to the mail piece thickness, said thickness measuring means comprising a part (20,46) connecting to and movable with the singulator (35) and a fixed part (8), the measured thickness being related to the relative amount of movement between said moving and fixed parts. Apparatus as set forth in claim 2 wherein the said moving part comprises a magnet (20), and the said fixed part comprises a magnetic field detector (8). Apparatus as set forth in claim 2 or 3 further comprising means (37) for temporarily stopping the mail piece when it is under the singulator (35). Apparatus as set forth in claim 2 or 3, further comprising means for moving the movable member (38) of the singulator (35) where it contacts the mail piece surface in a direction generally reversed with respect to travel of a singulated mail piece. Apparatus as set forth in claim 1, wherein the measuring means comprises means (20) for generating a magnetic field pattern, an array of magnetic field detectors (10 to 16) for outputting a binary signal in response to the field pattern, said field generating means (20) and detectors (10-16) being configured such that the outputted binary signal is absolute and Gray encoded over a range of thicknesses of the mail, and means connecting the singulator (35) and field generating means (20) for moving the latter past the array over a distance proportional to the movement of the singulator. Apparatus as set forth in claim 6, wherein the field generating means (20) is a magnet (22) having plural poles (24,25) arranged in a row, a first pole segment, a second pole segment, and a third pole segment of the same type as the first pole, the three segments having different lengths, the magnetic field detectors (10-16) being equally spaced apart. Apparatus as set forth in claim 7 wherein the detector array comprises Hall-effect detectors.

Inventors: DOLAN DONALD T, TOLMIE ROBERT J JR, DOLAN, DONALD T., TOLMIE, ROBERT J., JR.
Applicants: PITNEY BOWES INC, PITNEY BOWES, INC.
Application year: 1989
Main classification: B07C1
IPC codes: B07C1, G01B7, B65H7