Method for obtaining an image of a rolled fingerprint

Abstract

The invention relates to the field of biometrics and fingerprint identification, and more particularly to methods for taking fingerprints. The invention solves the problem of automatically obtaining complete and good-quality fingerprints. The technical results, which consist in a more complete fingerprint and an automated process, are achieved in that a contact surface of a fingerprint sensor is rotated around a digit which is clamped thereto, wherein a clamping device acts on the digit to improve contact between the digit and the sensor and synchronized movement of the clamp and the sensor ensure that the digit remains immobile, an electric signal from the sensor is processed and the image is recorded in a memory device.

Description

[0001] METHOD FOR OBTAINING AN IMAGE OF A ROLLED FINGERPRINT

[0002] Field of technology to which the invention relates

[0003] The invention relates to the field of biometrics, more precisely, to fingerprinting, namely, to methods for taking fingerprints.

[0004] Terms and definitions

[0005] For the purposes of this description, the following terms are used with the meanings specified below.

[0006] The term "contact" means a surface, part or device intended for direct contact with a particular part of a finger during the process of obtaining a fingerprint.

[0007] The term "flat sensor" refers to a device in the form of a three-dimensional device or a flat multilayer structure, equipped with a contact surface capable of detecting the fingerprint pattern of the area of ​​the finger pressed against it and converting this pattern into an electrical signal. Flat fingerprint sensors are known to exist in the form of a chip, a film on a rigid flat support, or an optical system with a transparent prism. A fingerprint sensor operating on one or another principle, whether contained in a separate housing or installed in a common housing with another device, is called a fingerprint scanner.

[0008] The term "longitudinal axis of the sensor" refers to the axis of symmetry of the sensor's contact area, along which the finger is applied during rolling. The longitudinal axis of the sensor lies in the plane of the contact surface. The term "transverse direction" refers to the direction perpendicular to the longitudinal axis of the sensor and parallel to the plane of the contact surface.

[0009] The term "press" means the contact part, the part of the pressing device that touches the finger immediately before rolling and during the rolling process.

[0010] The term "rolling" refers to the well-known process of obtaining a rolled fingerprint by rolling a finger over the contact surface of a flat sensor or over paper.

[0011] The term "rolling" refers to the proposed process of producing a rolled fingerprint by mechanically rolling the finger onto the contact surface of a flat sensor.

[0012] The term "drive" means a combination of an engine, transmission and control system designed for controlled movement of a moving part of a device.

[0013] The term "program" means application software for controlling a fingerprint scanner, and in the case of automatic execution of the claimed method, also for controlling the drives of the moving units of the rolling device.

[0014] State of the art

[0015] The most informative type of fingerprint is the rolled fingerprint, obtained by rolling a finger across a piece of paper or the contact surface of a fingerprint sensor, such as the sensing face of a fingerprint scanner's optical prism. The technology for producing rolled fingerprints on fingerprint scanners, including methods for combining sequentially read pattern fragments into a complete fingerprint, is known and disclosed, in particular, in patent publications US 5748766 A, RU 2051415 C1, and WO 01 / 77997 A1. Rolled fingerprints are used to create fingerprint maps and are stored and compared in fingerprint search systems.

[0016] For less complex fingerprinting systems, a fingerprint is often sufficient, as it is significantly easier to obtain than a rolled fingerprint. Fingerprint scanners designed for fingerprint capture are also simpler. A disadvantage of a fingerprint is the small portion of the pattern captured, which limits its use primarily to biometric locks and sensors for authorization in electronic devices. A known method for obtaining a fingerprint similar in size to a fingerprint is by dragging a finger across a linear sensor, then assembling the image from the scanned lines. A rolled fingerprint, compared to a fingerprint, has lower image quality. Furthermore, if the sensor is contact-based, pattern deformations are inevitable due to skin shear during scanning. For these reasons, fingerprints and rolled fingerprints cannot replace rolled fingerprints for fingerprinting purposes.

[0017] A search system requires both high-quality and complete fingerprints, as traces at crime scenes can be left by any part of the finger. The more complete the fingerprint, the higher the success rate of fingerprint analysis. Fingers must be rolled "from fingernail to fingernail" and meet many other requirements. Only a trained and experienced operator can consistently obtain correctly rolled fingerprints.

[0018] The following defects are common in fingerprints obtained by rolling: incomplete representation of the papillary pattern, especially in the lateral zones due to incomplete finger rotation; uneven fingerprint density due to variable finger pressure on the sensor; and fingerprint smearing due to misalignment of rotation and translation. The presence of these defects reduces the identification quality of the fingerprint, so eliminating them can improve the effectiveness of fingerprinting, particularly by increasing the number of fingerprint identifications at crime scenes. Ideally, the fingerprint should reproduce the entire fingerprint pattern of the nail phalanx of finger 1 (see Fig. 1). In this case, identification of a fingerprint left by any area of ​​the phalanx becomes possible.

[0019] In practice, rolling makes it possible to obtain an imprint containing the basal zone 2 together with the flexor fold 3, the central zone 4, partially the lateral zones 5 and 6, and partially the distal zone 7.

[0020] A small trace in which only a part of the pattern is displayed (for example, the edge of the lateral zone), which is not displayed on the rolled print, cannot be identified.

[0021] The need for complete and high-quality prints forces the development of new technical devices to facilitate the process of taking prints and reduce the number of defects.

[0022] Methods for obtaining fingerprints using contactless photography are known, but they are not yet sophisticated enough to replace the rolling method. Furthermore, a photographic image of a finger's surface differs significantly from a fingerprint image obtained by contact, making them difficult to compare, making it impractical to simultaneously use different types of images in a single biometric process.

[0023] Another known method, disclosed in US Patent No. 10,699,097, involves wrapping a flexible sensor around a finger and capturing the entire fingerprint. A drawback of this method is low image quality due to the varying pressure of the sensor on different areas of the finger. This method contains an unresolved contradiction: a sensor that is too rigid bends with longitudinal creases, which creates streaks along the finger, which can be seen in the image of the resulting fingerprint presented in the publication. A sensor that is too soft reveals the levers supporting the sensor, resulting in streaks across the finger, which can also be seen in the image. Apparently, the service life of such a sensor will also be limited due to repeated deformations with each scan.

[0024] Features of the analogue US 10699097 that coincide with or are similar to the features of the claimed invention:

[0025] • a method for obtaining an image similar in degree of completeness to the image of a rolled fingerprint;

[0026] • the method involves pressing a finger against the sensor of a contact fingerprint scanner;

[0027] • the method includes processing an electrical signal from a sensor;

[0028] • the method includes recording an image into a storage device.

[0029] Another known method, disclosed in patent application US 5,818,956 A, places a finger inside a concave transparent element, and then records a video of the fingerprint using a camera moving around the transparent element. A disadvantage of this method is that the fingerprint is incomplete, as the lateral areas are not adjacent to the sensor, at least not simultaneously. Another disadvantage is the reduced skin pressure on the sensor due to the increased area of ​​skin being pressed simultaneously, which is insufficient for good fingerprint quality. Another disadvantage of the concave sensor is that the quality of the resulting fingerprints depends on the size and shape of the finger.

[0030] Features of the analogue US 5818956 A, coinciding or similar to the features of the claimed invention:

[0031] • a method of obtaining an image that is more complete than an impression but less complete than a rolled fingerprint; • the method involves pressing a finger against the sensor of a contact fingerprint scanner, but the sensor is not flat, but concave;

[0032] • it is not the contact plane that is rotated around the finger, but a contactless photoreceiver;

[0033] • the method includes processing an electrical signal from a sensor;

[0034] • the method includes recording an image into a storage device.

[0035] Another application, US 5748766 A, details a technology for swiping a finger on a fingerprint scanner with a flat sensor. The process involves an operator and the person being fingerprinted (hereinafter referred to as the "fingerprintee").

[0036] To perform a finger roll, the operator holds the subject's hand with one hand and sets the initial rotation angle. Using the fingers of the other hand, the operator presses the finger against the sensor, maintaining a constant pressure. Rolling involves rotating the hand around the finger's longitudinal axis while simultaneously moving the finger laterally, applying even pressure. A full finger roll requires rotating the finger 180 degrees. During the process, the finger should successively touch the contact surface in different areas to ensure the scanner captures the most complete fingerprint possible.

[0037] Features of the analogue US 5748766 A, coinciding with the features of the claimed invention:

[0038] • method for obtaining an image of a rolled fingerprint;

[0039] • the method involves pressing a finger against the sensor of a contact fingerprint scanner;

[0040] • the scanner sensor is flat;

[0041] • the method includes processing an electrical signal from a sensor;

[0042] • The method involves recording the image in a storage device. The known method does not allow for a consistent production of a fully rolled fingerprint due to the need to rotate the hand into an uncomfortable position. It is not possible to automate the known method due to the practical impossibility of correctly independently rolling a typical fingerprint.

[0043] The problem with the well-known rolling method is the need to obtain a high-quality image of the rolled fingerprint, with full coverage of the lateral zones of the fingerprint pattern. This is hampered by the fingerprint recipient, who instinctively interferes with the complex movement orchestrated by the operator. This interference can manifest itself in tensing the hand muscles, attempting to assist the rolling, attempting to hinder the rolling, or attempting to avoid discomfort during the forced 90-degree rotation of the hand. When two people simultaneously control the movements of a single finger, the movements are difficult to coordinate, which degrades the quality of the fingerprint.

[0044] This problem occurs both when rolling a painted finger on a paper form and when rolling without paint using a fingerprint sensor.

[0045] A step towards solving this problem is described in patent publication JP 4552197 B2 (application JP 2007048116 A).

[0046] A device with a flat sensor panel for obtaining rolled fingerprints is disclosed. The panel is mounted so as to be rotatable about an axis located below the rolling area (Device Version 2) or to the side of it (Device Version 3).

[0047] The publication also describes fingerprint acquisition methods corresponding to the device variants. A rule is mentioned for rolling the finger across the sensor in one of two directions, one for each hand (right hand fingers from left to right, left hand fingers from right to left). This rule reduces the discomfort experienced by the fingerprint recipient when rolling their finger horizontally. In fingerprinting practice, this formula, "from an uncomfortable position to a comfortable one," was known even before the advent of fingerprint scanners and was used in the production of paper fingerprint cards. The existence of this rule confirms the discomfort experienced by any fingerprint recipient during the rolling process. In addition to individuals with normal physiology, fingerprinting also involves individuals with limited joint mobility due to pain syndromes or contractures.For them, turning the wrist to an angle sufficient for rolling can be painful, and sometimes even impossible.

[0048] The description of JP 4552197 B2 notes that obtaining a rolled fingerprint requires the skill of rotating and moving the finger across the sensor.

[0049] This remark is also true, to a greater or lesser extent, for all the methods for obtaining a print proposed in JP 4552197 B2.

[0050] It should be noted that rotation and translation must occur simultaneously, in the proper proportions, and while maintaining the proper finger pressure on the sensor, without creating shear stress in the finger at the point of contact. To achieve this, the finger must always apply pressure perpendicular to the sensor surface at every point of rolling or oscillating. JP 4552197 B2 does not disclose the technical means or method by which this can be achieved.

[0051] Using devices based on JP 4552197 B2, compared to rolling on a horizontal surface, is complicated by the fact that to establish contact with the sensor, the fingerprint recipient must press their finger against an inclined surface, somewhat to the side. As the sensor surface rotates, the direction of pressure must be adjusted accordingly, while refraining from rotating the finger. In this case, an untrained user should expect uneven pressure on the sensor, resulting in a higher rate of rejections and repeated fingerprint acquisition attempts.

[0052] The maximum angle to which the sensor can be rotated to obtain a full fingerprint is also not disclosed. Based on the figures in JP 4552197 B2, the sensor rotation angles range from -45 degrees to +45 degrees, which is clearly insufficient to obtain a fingerprint pattern on the outer edges of the lateral zones. There is no reason to assume that a rotating sensor without the operator's finger or a clamping device will reliably produce a rolled fingerprint by rotating the sensor at angles from -90 degrees to +90 degrees. This known method does not ensure the full width of the rolled fingerprint.

[0053] That is, the problem of "obtaining rolled fingerprint images with good image quality, regardless of the user's experience and skills," specified in JP 4552197 B2, is not solved by the devices disclosed therein.

[0054] Thus, the disadvantage of the JP 4552197 B2 equivalent is the need to instruct the user on the swiping procedure, the finger pressure, and the direction of this pressure, monitor the quality of the resulting fingerprints, and correct image deficiencies by re-capturing the fingerprints. Devices that do not maintain consistent fingerprint quality cannot provide adequate throughput for fingerprinting stations with a high volume of fingerprinted individuals.

[0055] Patent JP 4552197 B2 is the closest analogue of the claimed invention and is accepted as a prototype.

[0056] Disclosure of the essence of the invention

[0057] The technical challenge lies in the need to obtain a high-quality image of the rolled fingerprint, fully capturing the lateral zones of the fingerprint pattern. This is hampered by the fingerprint recipient, who instinctively interferes with the complex movement orchestrated by the operator. This interference can manifest itself in tensing the hand muscles, attempting to assist the rolling process, attempting to hinder the rolling process, or attempting to avoid discomfort during the forced 90-degree rotation of the hand. When two people simultaneously control the movements of a single finger, the movements are difficult to coordinate, which degrades the quality of the fingerprint.

[0058] This problem occurs both when rolling a painted finger on a paper form and when rolling without paint using a fingerprint sensor.

[0059] The technical result consists in increasing the completeness of the rolled fingerprint image.

[0060] The technical result is ensured by a combination of the following essential features:

[0061] 1. The method is designed to obtain an image of a rolled fingerprint.

[0062] 2. The method involves pressing a finger against the sensor of a contact fingerprint scanner.

[0063] 3. The scanner sensor is flat.

[0064] 4. The method includes processing an electrical signal from a sensor.

[0065] 5. The method includes recording an image into a storage device.

[0066] 6. The contact plane of the sensor is rotated around the finger pressed against it so that the sensor successively comes into contact with the lateral, central and other lateral parts of the nail phalanx of the finger.

[0067] 7. The finger is pressed with a clamping device to improve contact between the finger and the sensor. 8. As the sensor rotates, the clamping device and the sensor are moved in opposite directions, parallel to the sensor's contact plane, synchronously and by equal amounts.

[0068] The problem of obtaining a fully rolled fingerprint with good image quality is solved by shifting the task of maintaining proper finger contact with the sensor from the user to an automated device. To achieve this, the finger, while being rolled by the sensor, is moved along the plane of the sensor's contact surface. This device maintains contact with the sensor by a clamping device, which synchronously and by the same amount moves the clamping device in the direction opposite to the sensor's movement.

[0069] The user is required to do nothing other than place their finger on the device, wait for the end-of-roll signal, and then remove their finger. This makes the process of taking a swept fingerprint automatic and requires no operator intervention.

[0070] The proposed method differs from the prototype in the following features listed above: the contact plane of the sensor is rotated around the finger pressed against it; the finger is pressed with a pressing device to improve the contact of the finger with the sensor,

[0071] 1. The contact plane of the sensor is rotated around the finger pressed against it.

[0072] 2. The finger is pressed with a pressure device to improve contact between the finger and the sensor.

[0073] 3. During the process of turning the sensor, the clamp and the sensor are moved in directions parallel to the contact plane of the sensor, in opposite directions, synchronously and by an equal amount.

[0074] Essential features influence the technical result as follows: The rolled image is the most informative, as it displays the maximum possible area of ​​the papillary pattern of the fingernail phalanx. Furthermore, it is the rolled fingerprints that are necessary for creating fingerprint maps.

[0075] The contact method of obtaining prints provides a quality of pattern that is currently unattainable by other methods, and also uses a method of trace formation that is as close as possible to the process of leaving fingerprints on objects at crime scenes.

[0076] A flat sensor ensures consistent fingerprint formation conditions independent of finger positioning. Curved (non-flat) sensors known from the prior art do not provide consistent skin-to-sensor contact conditions, which alters the pressure in the contact zone and can introduce additional deformations into the fingerprint pattern.

[0077] With the same finger pressure, the contact area of ​​the finger with a concave sensor is larger than with a flat sensor, and the skin pressure on the sensor is lower. Furthermore, the pressure varies across the contact area. The fingerprint image appears fainter, with areas of dry skin and fragments of papillary lines appearing weakly.

[0078] With the same finger pressure, the contact area of ​​the finger with a convex sensor is smaller than with a flat sensor, and the skin pressure on the sensor is greater. The area of ​​skin visible when rolling on a convex sensor is reduced because the entire lateral area of ​​the phalanx is not visible at maximum finger rotation.

[0079] A full roll on a convex sensor would require increasing the finger's rotation angle relative to the sensor, which is beyond the physical capabilities of many people. Furthermore, excessive deformation of the fingerprint pattern is possible. Rotating the sensor around the finger eliminates the need to rotate the finger itself, allowing the rotation angle to be increased to a value sufficient to fully reproduce the fingerprint.

[0080] When rolling the finger with the sensor, all the same pattern zones are displayed as when rolling the finger on paper or over the sensor: the basal, central, partially distal, and both lateral zones. The sequence of reading the various zones of the fingerprint pattern mentioned in the formula is not an exclusive list of the zones displayed, but is provided only to indicate the direction of the sensor's rotational movement. Unlike rolling, rolling allows for a complete display of the lateral zones, since hand movement is not required, and the sensor can be mechanically rotated to any desired angle, up to a full rotation. Rotations of plus 90 degrees and minus 90 degrees from the center of the fingertip are sufficient for a full display. To achieve the technical result, only rotating the sensor is sufficient. The same result can be achieved by rotating the entire scanner.

[0081] The sensor is rotated using a mechanical rotating device, which directs the sensor's movement so that the sensor's contact patch with the finger describes a semicircle around the finger's longitudinal axis. Although the finger is not perfectly cylindrical, its cross-sectional shape near the joint is approximately circular.

[0082] The rotary device is driven by an electric drive. The entire running-in process can be fully automated using existing technology. To achieve this, all moving parts of the rotary device are equipped with electric drives controlled by software.

[0083] To obtain an image, the sensor must not slip on the finger. Therefore, during the break-in process, the contact patch shifts across the sensor (see Fig. 4), similar to what happens when rolling a finger over a stationary sensor. Following the contact patch, the finger must also shift across the sensor; otherwise, slippage will occur and the image will be blurred.

[0084] During a fingerprint scan, the movement of the finger's contact patch with the sensor is compensated for by shifting the finger's axis parallel to the sensor in a transverse direction, in the direction of finger rotation. This finger movement is controlled by the operator, as the fingerprint subject lacks the experience and / or motivation to independently coordinate the finger's movement and rotation.

[0085] During the rolling of the fixed finger by the rotating sensor, the contact patch also shifts from one edge of the sensor to the opposite edge.

[0086] The proposed rolling-in option facilitates fingerprinting for individuals with limited hand mobility. It eliminates the need to rotate the hand to display the lateral areas of the fingerprint.

[0087] The problem with known fingerprinting methods, as well as the method disclosed in the prototype, is the inevitable occurrence of a certain percentage of unsuccessful fingerprinting attempts, requiring a second attempt on the same finger. The instinctive tension of the fingerprinting subject, whether they are trying to assist the process, hinder it, or simply avoid discomfort, often leads to variations in the pressure applied to the sensor, resulting in fingerprints containing thinner and thicker areas, while some areas may not be captured at all or may be smeared.

[0088] The technical result consists in reducing the number of unsuccessful rolling attempts requiring repeated taking of the same imprint.

[0089] The technical result is achieved by applying pressure to the finger using a clamping device to prevent the finger from slipping along the sensor during the sensor running-in process.

[0090] The fingertip maintains contact with the sensor by applying pressure toward the sensor. Constant finger pressure on the sensor improves image uniformity.

[0091] The pressure device is capable of providing sufficient, limited, and uniform finger pressure on the sensor. The finger should be pressed firmly enough to ensure that, due to the elasticity of the soft tissue, both the flexor fold and a significant portion of the distal zone touch the contact surface simultaneously. At the same time, the pressure should be limited to avoid distorting the papillary pattern beyond what typically occurs during fingerprint formation. Furthermore, moderate pressure does not cause discomfort to the fingerprint recipient. The pressure device is designed to move the clamp itself, which can be, for example, an elastic bar. It can be mechanical or automatic and contain a combination of known kinematic components, such as levers, sliders and guides, springs, and pneumatic or electric drives.

[0092] In rare cases, a fingerprint subject undergoing the initial warm-up process may be confused by even slight forced finger movements. Their reaction may be an instinctive attempt to rotate their finger to follow the sensor or to pull their hand away. The fingerprint may be damaged, requiring a second warm-up. For the fingerprint subject's comfort, it's important to ensure there's no reason to move their finger during the warm-up process and to keep it as still as possible.

[0093] The technical problem is the pin's displacement during break-in, which can cause discomfort or interfere with the break-in process. The technical goal is to minimize pin axis displacement during break-in.

[0094] To keep the finger in place, compensation for the impact on the finger caused by the circular movement of the sensor is achieved by shifting the sensor relative to the axis of rotation in the direction opposite to the rotation, and simultaneously shifting the clamp in a direction parallel to and opposite to the displacement of the sensor.

[0095] At any angular position of the sensor, the clamp and the sensor are located on opposite sides of the finger, and the simultaneous displacements of each of them in the direction opposite to the rotation of the rotary unit with the sensor and clamp installed on it are parallel to the contact plane of the sensor and are directed in opposite directions.

[0096] The displacement of both the sensor and the clamp can be accomplished by known means, for example, by moving the sliders to which they are attached along guides mounted parallel to the sensor's contact surface. To ensure simultaneous displacement, the sliders can be linked by a lever or other transmission. Alternatively, each slider can be moved by a separate drive, and the synchronicity of movement can be ensured by a control program. The slider movement is proportional to the sensor's rotation angle, so that the sensor displacement and the clamp's displacement equal the displacement of the contact patch.

[0097] Another technical issue is the occasional small angular movements of the fingers. A constant ratio between the rotation and displacement of the sensor does not fully compensate for the sensor's rotation due to the variability of finger sizes and shapes, even on the same hand, and especially between individuals. Deviations in actual sizes from the average values ​​implied by the rotation and displacement ratios of the sensor and the pressure force result in the finger being somewhat involved in a rotational motion during rolling, either with or against the rotation of the sensor. This issue is addressed by tracking finger movements and, depending on the resulting finger rotation angle, adjusting the displacement ratio of the pressure force and sensor relative to the rotation angle of the sensor. Rotation tracking can be accomplished using known methods, such as neural network analysis of a finger image captured by a stationary camera.

[0098] Another problem being solved: existing methods of obtaining a fingerprint by rolling require operator involvement. Consequently, labor costs arise. The operator's first task is to maintain contact between the rolled finger and the sensor surface, and the second is to control the correct movement of the finger across the sensor. The prototype does not specify the technical means for solving this problem.

[0099] It is assumed that the person being fingerprinted will solve the problem independently. In this case, the operator must provide preliminary instructions, monitor the process, take corrective actions, and then monitor the results.

[0100] The claimed method solves the first problem by holding the finger on the sensor with pressure. The second problem is solved by rolling the finger over the sensor, while the finger itself essentially remains in place.

[0101] The third task of the operator—initiating and completing the process of reading the fingerprint by the sensor, followed by recording it in the storage device—is currently automated through the program's analysis of the current image on the sensor and is used when rolling on most known fingerprint scanners.

[0102] The technical result consists in automation of the fingerprinting process.

[0103] This technical result is achieved by first pressing the central part of the phalanx against the sensor. The sensor is then rotated around the finger until it contacts one of the lateral parts. A new image is then recorded, and the sensor is rotated in the opposite direction to the other lateral part of the nail phalanx. A similar technique is known to be used during rolling, where it is useful for initially centering the finger on the sensor, especially for scanners with a small contact surface. In the claimed rolling method, centering the finger can be accomplished using a support for the part of the finger not covered by the sensor, and the above technique is used to obtain a test image and automatically decide whether to perform the rolling or re-attach the finger to the sensor.

[0104] To automate the fingerprinting process, one can use established tools: moving kinematic links equipped with drives and a well-known program that controls the fingerprinting process, including monitoring the fingerprint image on the sensor, capturing the moving contact patch frame by frame, assembling the fingerprint fragments, and storing them in a memory device. The program is supplemented with drive control functions. When a fingerprint pattern appears on the sensor, the program automatically moves the clamp toward the finger and sequentially rotates the sensor. When the sensor rotates, it automatically shifts the sensor and clamp using a shift drive, ensuring the finger is held in place during the fingerprinting process. To obtain a fingerprint, the person being fingerprinted simply places their finger on the sensor and waits for the fingerprinting process to complete, at the end of which the clamp automatically moves away from the finger.

[0105] As a result, the need for an operator is eliminated. Brief description of the drawings

[0106] Fig. 1 shows a schematic representation of the nail phalanx, viewed from the fingertip. Dashed lines delineate the zones of the papillary pattern.

[0107] Fig. 2 depicts three sequential phases of the known method of rolling a finger across a sensor, viewed from the fingertip. The arrows indicate the rotation of the finger around its axis and the accompanying transverse displacement of the finger across the sensor.

[0108] Fig. 3 depicts three successive phases of the claimed method for rolling a stationary finger with a sensor, viewed from the fingertip. The arrows indicate the rotation of the sensor around the finger axis and the accompanying transverse displacement of the sensor relative to the finger.

[0109] Fig. 4 shows the contours of the contact patch on the surface of a rectangular sensor, corresponding to both the rolling phases shown in Fig. 2 and the running-in phases shown in Fig. 3. The contact patch is viewed from the sensor side. The arrows indicate the direction of displacement of the contact patch along the sensor during rolling or running-in.

[0110] Fig. 5 shows a kinematic diagram of the pin rolling process.

[0111] Fig. 6 shows the relative positions of the sensor, finger, and clamp in the sensor's mid-position. The contact patch is in the central zone. The arrow indicates the direction of the force applied to the clamp to maintain contact with the sensor.

[0112] Fig. 7 shows the relative positions of the sensor, finger, and clamp in the sensor's first extreme position. The contact patch is in the lateral zone. The curved arrows indicate the direction of future rotation of the frame, including the sensor and clamp, for the primary scan. The straight arrows indicate the directions of future movement of the sensor and clamp for the primary scan. Implementation of the invention

[0113] The method can be implemented using a known fingerprint scanner as a sensor, provided that the scanner meets the following requirements: a) it is designed for rolling fingers, and not only for obtaining impressions; b) the shape of the contact surface is flat; c) according to the operating conditions of the scanner, it is allowed to tilt it at angles of plus or minus 90 degrees during rolling;

[0114] In particular, a scanner with an optical prism as a contact element of the sensor, made according to patent RU 58889 U1, is suitable.

[0115] The method was implemented using a well-known DS-22N fingerprint scanner, designed for finger rolling, but in this case used as a rolling sensor. The scanner is connected to a computer running an application program that controls the rolling process. The scanner is designed to sequentially capture fragments of the fingerprint pattern displayed on the contact patch as the fingerprint is rolled, convert the images into an electrical signal, and transmit this signal to the program, which combines the fragments into a single rolled fingerprint.

[0116] A scanner 9 and a clamping device are mounted on a rotating frame 8 (see Fig. 5) with the ability to move laterally. A clamp 11 made of elastic material is attached to the movable link 10 of the clamping device. The drives of the movable links are not shown. The contact surface of the sensor 12 and the clamp 11 form a gap into which the finger 1 to be scanned is placed.

[0117] When ready to receive a fingerprint, the scanner is positioned horizontally, with the sensor contact surface facing upward. The clamp is retracted from the sensor. The program analyzes the signal from the scanner and waits for an image to appear. The fingerprint recipient places finger 1 on the contact surface along the longitudinal axis of sensor 12 (see Fig. 6). The program detects the image and activates the clamping device, which moves clamp 11 toward the finger. The clamp applies a force limited to 0.8 - 1.6 kgf and maintained approximately constant, which is optimal for obtaining the best fingerprint quality on this scanner. The limited force and elasticity of the clamp allow the user to withdraw their hand in case of discomfort or fright, at any point during the testing period.

[0118] After pressing the finger against the prism, the program recognizes the fingerprint pattern in contact patch 13, and the frame begins a trial rotation around the finger. The sensor rolls around the finger pressed against it, moving from the central area of ​​the phalanx to the lateral side—that is, from the center of the pad to the lateral edge of the nail. Meanwhile, the clamp rolls around the finger from the opposite side, remaining parallel to the sensor. To prevent the finger from being drawn into rotational motion, the clamp moves parallel to the sensor in sync with the frame rotation. The trial rotation of the frame is performed to assess the suitability of the resulting image and to move the sensor and clamp to the first extreme position (see Fig. 7), which is the initial position for the main scan. The main scan will be performed in one continuous movement from the first extreme position of the sensor to the second extreme position.

[0119] Upon reaching the first extreme position, corresponding to the maximum rotation angle (approximately plus 90 degrees), the frame automatically stops. If, during the test rotation, the program obtains a normal sequence of fingerprint fragments with a sufficient image quality, it immediately begins rotating in the opposite direction, to the second extreme position of the frame (approximately minus 90 degrees). The sensor rolls the finger from one lateral zone to the opposite lateral zone. The program then sequentially obtains image fragments for a complete fingerprint "from nail to nail."

[0120] At the second extreme position, the frame stops and the clamp automatically releases from the finger. The program processes the signal received from the sensor and records the assembled image of the rolled fingerprint fragments into the memory device.

[0121] The offset of the clamp relative to the sensor prevents the finger from rotating with the scanner. Some finger movement is inevitable during the rolling process, due to individual differences in finger size and shape, but this movement is several times smaller than required for standard rolling. This method does not require any special movement or rotation of the hand during the rolling process.

Claims

Formula 1. A method for obtaining an image of a rolled fingerprint, which includes pressing a finger against a flat sensor of a contact fingerprint scanner, processing an electrical signal from the sensor and recording the image in a memory device, in which the contact plane of the sensor is rotated around the finger pressed against it so that the sensor sequentially comes into contact with the lateral, central and other lateral zones of the nail phalanx of the finger, while the finger is acted upon by a pressing device to improve contact of the finger with the sensor, characterized in that during the process of turning the sensor, the pressing device and the sensor are moved in directions parallel to the contact plane of the sensor, in opposite directions, synchronously and by an equal amount.

2. The method according to paragraph 1, characterized in that the central zone of the phalanx is first pressed against the sensor, then the sensor is rotated around the finger until it contacts the outer border of one of the lateral zones, after which recording of a new image begins and the sensor is rotated in the opposite direction to the outer border of the other lateral zone of the nail phalanx of the finger.

3. The method according to paragraph 1, characterized in that when the sensor is rotated, the clamp and the sensor are moved automatically by means of a displacement drive.

4. The method according to paragraph 3, characterized in that the displacement drive is controlled depending on the current angle of rotation of the sensor.

5. The method according to paragraph 4, characterized in that the clamp and the sensor are displaced proportionally to the angle of rotation of the sensor.

6. The method according to paragraph 4, characterized in that the movements of the finger are tracked and, depending on the angle of rotation of the finger, the proportion of the displacement of the clamp and the sensor is adjusted in relation to the angle of rotation of the sensor.

Images