JP2016014860A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform, when there are a plurality of heat sources to heat a fixing member, temperature control of the plurality of heat sources with a temperature sensor common to the heat sources.SOLUTION: There is provided a fixing device including a fixing member, a plurality of heat sources for heating the fixing member, a pressure member that presses the fixing member to form a fixing nip part, a sensor that detects the surface temperature of the fixing member, and heating control means for controlling the plurality of heat sources on the basis of the temperature detected by the sensor. The fixing device uses a multi-eye thermopile array as the sensor, allocates a plurality of detection elements of the thermopile to each of the plurality of heat sources, uses one of the plurality of detection elements allocated to each of the heat sources to temperature control of the heat sources based on a set target temperature, uses the rest of the detection elements to detect the maximum temperature or minimum temperature, and when the detected maximum temperature exceeds a threshold, decreases the target temperature, and when the detected minimum temperature is below another threshold, increases the target temperature.

Description

  The present invention relates to an image forming apparatus such as an electrophotographic copying machine, a printer, and a facsimile, and more particularly to a heating type fixing device mounted on such an image forming apparatus.

  In an electrophotographic image forming apparatus, a toner image is formed on an image carrier based on image information, the toner image is transferred onto a recording material such as paper or an OHP sheet, and the recording material carrying the toner image is fixed. The toner image is fixed to the recording material by heat and pressure through the apparatus.

  A fixing device for fixing a toner image on a recording material is usually composed of a pair of rollers each composed of a fixing roller and a pressure roller facing each other, or a fixing belt and a pressure roller wound around a plurality of rollers. The toner image is fixed by heat and pressure through the recording material. As a heat source in the fixing device, various modes such as a halogen heater, electromagnetic induction heating using a coil for generating magnetic flux or magnetic field lines, surf fixing using a ceramic heater, and a film belt method are known. The film belt system is configured to apply heat energy to the recording material by sandwiching the film and the recording material in close contact with a plate-shaped heat source that contacts the thin cylindrical heat-resistant film and a pressure roller.

  In order to obtain good image results in the fixing process, the surface temperature of a fixing member such as a fixing roller or a fixing belt heated by a heat source needs to be maintained at a target temperature higher than the melting and softening point temperature of the toner . Therefore, in order to control this, the fixing device is provided with a temperature sensor for detecting the surface temperature of the fixing member to be heated, and using the output value from the temperature sensor, the surface temperature of the fixing member is monitored. The temperature of the heat source is controlled so as to keep the surface temperature of the fixing member constant.

  On the other hand, since the fixing device generates heat, the demand for energy saving is particularly strong, the fixing member is required to have a short rise time and low energy loss, and the fixing member has a low heat capacity. However, as a result of the reduction in heat capacity, the temperature rise in the non-sheet passing region in the heated fixing nip portion tends to decrease rapidly. Many sensors are required to detect the temperature in the paper region, which increases the cost. Further, since temperature unevenness may occur even in the paper passing area, it may be required to arrange a plurality of sensors in the paper passing area. In order to solve such problems, it has been proposed to use a thermopile array as a temperature detection means for the fixing member. For example, in Patent Document 1, a thermopile array is used to detect abnormal heat generation in the fixing device. .

  Here, the thermopile is a sensor having a hot junction and a cold junction, and condenses infrared rays radiated from an object on a hot junction where a number of thermocouples are connected in series or in parallel, thereby cooling the thermopile. Temperature measurement is performed by generating an electromotive force according to the temperature difference from the junction. Since the measurement results differ depending on the temperature of the thermopile itself, especially the temperature of the cold junction, that is, the measurement results depend on the ambient temperature of the sensor, an ambient temperature sensor that measures the ambient temperature of the sensor is provided to compensate for the temperature change. doing.

  The thermopile array in Patent Document 1 is used to detect the temperature of the entire width or a partial area width of the fixing roller as a fixing member, and does not show the relationship with the heat source. It is the purpose of.

  An object of the present invention is to provide a temperature sensor common to a plurality of heat sources for heating a fixing member, and to control the temperature of the plurality of heat sources by the temperature sensor.

  The problems include a fixing member, a plurality of heat sources for heating the fixing member, a pressure member that forms a fixing nip portion with the fixing member by pressing the fixing member, and the fixing member In a fixing device having a sensor that detects a surface temperature and a heating control unit that controls the plurality of heat sources based on temperatures detected by the sensors, a multi-eye thermopile array is used as the sensor, and the plurality of heat sources A plurality of sensing elements of the thermopile are assigned to each of the heat sensors, and one of the sensing elements assigned to each of the heat sources is used for temperature control of the heat source based on the set target temperature, and the remaining detection If the element is used to detect the maximum or minimum temperature and the detected maximum temperature exceeds the threshold, the target temperature itself is lowered or the detected minimum temperature falls below another threshold. If, by raising the target temperature itself, it is solved.

  According to the present invention, a plurality of thermopile sensing elements are assigned to each of a plurality of heat sources, and one of the plurality of sensing elements assigned to each of the heat sources is assigned to a heat source based on a set target temperature. Used for temperature control, the remaining sensing element is used to detect the maximum or minimum temperature, and if the detected maximum temperature exceeds the threshold, the target temperature itself is lowered, or the detected minimum temperature is below another threshold Since the target temperature itself is raised, appropriate temperature control of a plurality of heat sources can be realized by one temperature sensor, and the cost can be reduced by reducing the sensor cost and its wiring cost.

1 is a schematic diagram illustrating a configuration of a monochrome printer which is an example of an image forming apparatus according to the present invention. FIG. 2A is a perspective view, and FIG. 2B is a conceptual diagram illustrating a positional relationship between a heat source and a temperature sensor in a fixing roller. FIG. 3A is a perspective view of a fixing device as an example of a fixing device according to the present invention, and FIG. 3B is a conceptual diagram showing a positional relationship between a heat source in a fixing roller and a thermopile. It is a figure explaining the arrangement | positioning position of a thermopile in case temperature control of these edge part heat sources is not performed integrally when the edge part heat source exists in both sides on both sides of the heat source for center area | regions. FIG. 5A is a diagram for explaining the distance of the thermopile when the end region heat source is on both sides of the center region heat source, and FIG. 5A is a diagram illustrating the position of the thermopile when measuring the temperature of only one end region heat source. 5b is a view relatively showing the position of the thermopile when the temperature of both end region heat sources is measured. It is a conceptual perspective view which shows the relationship between the cover and measurement window in the fixing device according to the prior art. FIG. 3 is a conceptual perspective view showing a relationship between a cover and a measurement window in the fixing device according to the present invention and a shutter mechanism that automatically closes the measurement window when the device is taken out. It is a figure explaining the state of an arithmetic circuit and an input-output line when increasing the number of detection simply with a thermopile array. It is a figure explaining the structure which shares an arithmetic circuit with respect to several detection element in the case of increasing the detection number by a thermopile array.

  As shown in FIG. 1, in a monochrome printer as an image forming apparatus according to an embodiment of the present invention, as is known, a predetermined printer necessary for forming an image around a photoconductor 8 as an image carrier. An apparatus, for example, a charging unit, an exposure unit, a developing unit, and the like are provided. That is, a charging roller 18 as a charging unit, a mirror 20 constituting an exposure unit, a developing device 22 having a developing roller 22a, a transfer device 10, a cleaning device 24 having a cleaning blade 24a, and the like are arranged. The exposure light Lb is irradiated and scanned between the charging roller 18 and the developing device 22 through the mirror 20 to the exposure unit 26 on the photosensitive member 8. A sheet feeding unit 4 is disposed at the lower part of the printer, and a registration roller pair 6 is provided in the middle of the paper conveyance path to the image forming unit, and a fixing roller 28 and a pressure roller 30 are provided at the end of the paper conveyance path. A fixing device 12 as a main constituent member is provided.

  The paper feed means 4 is a paper feed tray 14 that stores paper P as a recording material in a stacked state, and a paper feed roller that separates and feeds the paper P stored in the paper feed tray 14 one by one from the top. 16 etc. The paper P sent out by the paper feeding roller 16 is temporarily stopped by the registration roller pair 6, and after the position deviation is corrected, it is sent to the transfer site N by the registration roller pair 6 at a timing synchronized with the toner image on the photoconductor 8. It is done.

  The image forming operation in this printer is performed in the same manner as before. That is, when the photosensitive member 8 starts to rotate, the surface of the photosensitive member 8 is uniformly charged by the charging roller 18, and the exposure light Lb is irradiated and scanned on the exposure unit 26 based on the image information to correspond to an image to be created. An electrostatic latent image is formed. The electrostatic latent image is moved to a position facing the developing device 22 by the rotation of the photosensitive member 8, where toner is supplied to be visualized to form a toner image. The toner image formed on the photoconductor 8 is transferred onto the paper P that has entered the transfer portion N at a predetermined timing by applying a transfer bias by the transfer device 10. The paper P carrying the toner image is conveyed toward the fixing device 12, fixed by the fixing device 12, and then discharged and stacked on a paper discharge tray outside the apparatus. Residual toner remaining on the photosensitive member 8 without being transferred at the transfer portion N reaches the cleaning device 24 as the photosensitive member 8 rotates, and is scraped off by the cleaning blade 24 a while passing through the cleaning device 24. To be cleaned. Thereafter, the residual potential on the photoconductor 8 is removed by a known charge eliminating means and prepared for the next image forming step.

  Here, referring to FIG. 2, a fixing device of a central sheet passing mode according to the prior art will be described. The fixing device includes, for example, a fixing roller 28 that is a fixing member having a built-in heat source 27 and a pressure roller 30 that is a pressure member that forms a fixing nip portion by pressing the fixing roller. Instead of the fixing roller 28, a thin cylindrical belt or a heat resistant film with a reduced heat capacity may be used. In such a fixing device, in the prior art, as the heat source 27 for heating the fixing roller 28, for example, a center region heat source 27 ′ and an end region heat source 27 ″ covering an assumed sheet passing size are provided. One temperature sensor 31 and 32 is arranged for each heat source, and a power source 50 that supplies power to the heat sources 27 ′ and 27 ″ is controlled based on detection information of the temperature sensors 31 and 32. A heating control means 52 is provided. The heating control means 52 means a microcomputer including a CPU, ROM, RAM, I / O interface and the like.

  On the other hand, in the fixing device according to the embodiment of the present invention, as shown in FIG. 3, the two temperature sensors 31 and 32 in FIG. 2 are substituted by one thermopile array 33. That is, the thermopile array 33 in this example is a multi-eye sensor having eight sensing elements in one sensor, four sensing elements in the center region heat source 27 ', and another four in the end region heat source 27 ". Sensing elements are assigned and temperature is detected respectively. Based on the information obtained by the thermopile array 33, the heating control means 52 controls the power source 50 to supply appropriate power to both heat sources 27 ′ and 27 ″. Supply. As can be seen from the drawing, the plurality of detection elements of the thermopile array 33 perform temperature detection at different positions (temperature detection points) shifted from each other in the longitudinal direction of the fixing roller 28, that is, in the width direction of the sheet to be passed ( In some cases, it may be possible to shift the rotation direction of the fixing roller). One of the four sensing elements is always used for temperature control of each heat source, and the remaining three sensing elements are used for detecting the maximum temperature. In the constant temperature control, the heat source is turned on and off during the fixing process so that the surface temperature of the fixing roller falls within a predetermined temperature range with a preset target temperature (for example, 180 ° C.) interposed therebetween. is there. On the other hand, the maximum temperature detection is concerned with whether or not the detection temperature of each element exceeds a threshold value (for example, 190 ° C. higher than the set target temperature: outside the fixing good range). If the detected temperature exceeds the threshold value, the setting is changed to lower the target temperature itself. If the detected maximum temperature of the fixing roller surface exceeds the threshold value in any region of the roller surface, the deterioration of the fixing roller will be accelerated, so at multiple temperature detection points. It is avoided by temperature detection. It is assumed that the lowest temperature is detected instead of the highest temperature detected by a plurality of elements. When any of the temperatures detected by the plurality of elements is below the minimum temperature threshold (lower than the set target temperature, for example, 170 ° C .: out of the fixing good range), the setting is changed to increase the target temperature itself. This is because a fixing failure may occur in a state below the minimum temperature threshold.

  In this way, the cost can be reduced by controlling the two heat sources by the heating control means using one sensor (thermopile array). As the thermopile array, it is preferable to use a thermopile of a type in which a large number of detection elements are switched by one circuit to measure temperature. In this method, since the temperature is measured by switching each detection element, it takes time to measure, but only one cold junction or a temperature calculation CPU is required, which is suitable for cost reduction. As described above, the thermopile array 33 has eight sensing elements in one sensor, and two of them are used for heat source control, but the arithmetic circuit is also connected to the other six sensing elements. Temperature detection is possible.

  By the way, for image forming apparatuses for copying machines, sheets of various sizes are used. As shown in FIG. 3, in the fixing device having only two heat sources for the central region (central heat source / heating body) and the end region heat source (end heat source) as the heat source, the heating width of each heat source is as follows. The fixing roller (sleeve) is heated uniformly. Sheet conveyance is normally performed on the basis of the width center. Therefore, the heating width of the central heat source and the edge heat source is the shortest width of the most widely used paper width as the central heat source heating width, and the width area obtained by removing the short width from the long width is the edge heat source heating width. And often.

  In a state where the paper is idling without passing through the fixing nip, the temperature set in the center and the edge is compared with the detected temperature of the element used for heat source control, and the heat source is energized. Control is performed. Even when the sheet passes through the fixing nip portion, the operation for maintaining the temperature of the sleeve surface layer as described above is basically the same. However, if the paper width does not match the width of each heat source, for example, if the center heat source heating width <paper width <edge heat source heating width (the width including the connecting portion at the center), the outer edge of the edge heat source from the outside of the paper width In the sleeve range up to, the temperature may increase as the number of sheets to pass increases (edge temperature increase). This is because the temperature detection position of the edge heat source is within the paper width. At the temperature detection position, the heat is taken away by the paper, the temperature of the sleeve surface layer is lowered, and energization control is performed so as to heat it. This is because the heat quantity is not transferred to the sheet at the outer edge of the edge heat source.

  In the prior art, from the viewpoint of cost, a contact-type temperature sensor or the like is attached to the end of the pressure roller facing the fixing roller, and the sheet passing operation is interrupted when the temperature of the sensor exceeds a certain set value. In addition, an operation was carried out in which the temperature at the end temperature rise was leveled in the width direction by idling. This is a so-called productivity reduction called cpm down.

  There are two problems with such prior art. The first is an increase in cost due to the sensor arrangement on the pressure roller side, and it is difficult to arrange sensors in accordance with at least the main width sizes of various papers. Secondly, the temperature of the sleeve surface layer is estimated from the surface temperature of the pressure roller based on empirical rules, and the cpm is reduced. The surface temperature of the pressure roller where the cpm is put down is set low (approx. 200 ° C) in consideration of unexpected temperature differences. On the other hand, the heat resistance temperature of the fixing roller (sleeve) is small in the surface PFA layer. It is about 280 ° C. In short, productivity could not be pursued until the permissible temperature limit of the fixing roller.

  In the present invention, since a multi-eye type thermopile array (multi-point array sensor) is used for temperature detection, it is possible to directly detect the sleeve surface temperature at multiple points in the width direction without contact, and the end temperature rise A prominent part can be detected immediately and accurately. In addition, it is possible to raise the temperature at which cpm is reduced to the limit of the heat-resistant temperature of the surface PFA layer, so that productivity can be pursued more than before.

  In addition, by using a multi-point array sensor, it is possible to directly detect the sleeve surface temperature at multiple points in the width direction in a non-contact manner, thereby enabling temperature management within the paper passing area in the width direction in a finer range. . In the conventional fixing temperature control, as shown in FIG. 2, each sensor located in the approximate center of each heat source is a detection location, and the sleeve surface temperature unevenness in the width direction position that cannot be detected by the sensor, The control temperature (target temperature) was set after taking this into account. If temperature management is possible even in the width direction paper passing area in a finer range, temperature direction temperature unevenness and temperature sag can be detected one by one, so that control temperature setting including a margin becomes almost unnecessary. In addition, the state where the cpm is down is not a state where the fixing unit, for example, immediately after the return from sleep, particularly the pressure roller is in the vicinity of the normal temperature, and the pressure roller is sufficiently warmed to some extent. In this state, there is room for lowering compared to the control temperature at the beginning of paper feeding. If the control temperature can be lowered, for example, when the sleeve surface temperature outside the paper passing area approaches the heat resistance temperature, the point where the temperature is detected to be the lowest in the paper passing area is within a range that does not fall below the lower limit temperature for good fixing. Turn on the control to lower the control temperature from the initial stage. That is, if the detection value indicating the maximum temperature among the plurality of detection elements assigned to each heat source exceeds a threshold value set near the heat resistance temperature of the fixing roller, the minimum temperature in the sheet conveyance area is within the fixing good range. The temperature of the heat source is controlled by lowering the control temperature itself within a range that does not fall below the lower limit. As a result, the input energy outside the paper passing area is also reduced, and so-called edge temperature rise can be mitigated.

  When the end region heat sources 27 ″ are arranged on both sides of the center region heat source 27 ′ as in this example, both the end region heat sources 27 ″ are integrally formed, and the temperature control is performed. It is better to do it in pairs. Otherwise, as can be seen from FIG. 4, in order to measure the temperature for all the heat sources 27 ′, 27 ″, and 27 ′ ″ with one thermopile for cost reduction, the thermopile is separated from the fixing roller 28. If the fixing roller 28 is arranged at such a distance, the entire fixing roller can be measured, but when viewed from the cross-sectional side of the fixing roller 28, as shown in FIG. There is a negative effect that the area expands.

  At first glance, both seem to be able to measure the temperature of the fixing roller 28 in the same way, but when actually measured, the temperature detection accuracy decreases in the distant arrangement shown in FIG. This is because if the thermopile array is arranged far away (FIGS. 4 and 5b), reflection occurs at the end of the expanded detection range, and the temperature of the reflection destination is read, resulting in a decrease in detection accuracy. . In order to prevent the detection accuracy from being lowered by disposing the thermopile at a relatively far distance in the configuration in which the temperature is measured with respect to all the heat sources in the fixing member with one thermopile, the fixing member of the electromagnetic induction heating, the film belt method, etc. It is conceivable to increase the diameter. However, it is difficult to increase the size of the fixing member because it creates new problems such as arrangement restrictions in the image forming apparatus, deterioration of energy saving, and cost increase of parts. When the heat source for the end region is arranged on both sides across the heat source for the central region, only one thermopile is formed by integrally forming the heating regions at both ends as a pair, detecting the temperature only on one side, and controlling the temperature. With this, the temperature measurement and temperature control of the fixing member can be performed satisfactorily.

  It is also preferable that the thermopile array is attached to the image forming apparatus main body outside the fixing device, and the temperature of the fixing roller (fixing member) is measured from the outside of the fixing device. In this way, when the fixing device is removed from the image forming apparatus main body, the thermopile remains in the image forming apparatus, so that it is not subject to parts replacement, saves resources, and reduces costs when performing replacement services. Also contributes.

  When the thermopile array is attached to the main body of the image forming apparatus outside the fixing device, that is, when the thermopile array is left in the main body of the apparatus, it is necessary to take measures against harmful effects. The fixing device is covered with a cover made of resin or the like so that the operator does not get burned when performing operations such as replacement and jam release. When measuring temperature using a thermopile array placed outside the fixing device, it is necessary to enlarge the measurement window provided on the cover due to its structural characteristics, and the operator mistakenly presses the hot fixing roller (fixing member) from the measurement window. There is a possibility of touching. As shown in FIG. 6, one temperature sensor 31 and 32 is arranged for each heat source 27 ′ and 27 ″, which is a problem that may occur in the fixing device according to the prior art shown in FIG. Therefore, the measurement window 36 is not so large and can be devised so that the operator's finger does not enter.When using a thermopile array, there is a problem with having a shutter mechanism that closes the measurement window when the fixing device is taken out from the image forming apparatus. 7, the shutter mechanism is configured to mesh with the gear 38 attached to the unit body of the fixing device, the rack 39 attached to the shutter 42 so as to mesh with the gear 38, and the gear 38. The rack 40 is attached to the main body of the image forming apparatus, and when the fixing device is taken out of the main body of the image forming apparatus, the rack on the unit main body side is removed. 40 gear 38 is rotated by engagement of the gear 38 of the fixing device, the rack 39 by rotation of the gear 38 and hence the shutter 42 closes the measuring window 37 moves.

  As described above, the thermopile array used in the present invention is preferably a system in which a plurality of detection elements are switched and operated by a single circuit to measure temperature. In general, when the number of detections is simply increased in a thermopile array, the number of arithmetic circuits and input / output lines is very large as shown in FIG. 8, resulting in high cost. Therefore, as shown in FIG. 9, the cost is suppressed by using a common arithmetic circuit for a plurality of sensing elements. The configuration shown in FIG. 9 has a switch for connecting each element to the arithmetic circuit in order, and only the element connected to the arithmetic circuit can read the temperature. Since measurement takes place sequentially, it takes time to measure at all temperature detection points, but if measurement delays are a problem, increase the number of arithmetic circuits, for example, measure eight detector elements with two arithmetic circuits. Is also effective. In addition, a supply power cutoff circuit is incorporated in such an arithmetic circuit. Based on the calculated temperature data, the corresponding heat source is cut off by one or a number of calculation circuit supply power cut-off circuits. In order to ensure safety, the fixing device generally has a circuit that cuts off the supplied power when the sensor detects a high temperature above a predetermined level. In a sensor configuration that has a large number of arithmetic circuits corresponding to the number of detection elements, Therefore, it is necessary to provide as many cutoff circuits as the number of arithmetic circuits. However, by adopting a system in which the temperature of the sensor is collectively transferred with the configuration shown in FIG. 9, the number of cutoff circuits can be reduced, resulting in cost reduction. Note that the arithmetic circuit and the supply power cut-off circuit are known and will not be described again here.

12 Fixing Device 27 Heat Source 28 Fixing Roller 30 Pressure Roller 33 Thermopile Array

JP 2012-177790 A

Claims (8)

A fixing member, a plurality of heat sources for heating the fixing member, a pressure member that forms a fixing nip portion with the fixing member by pressing the fixing member, and a surface temperature of the fixing member are detected. A fixing device comprising: a sensor for controlling the plurality of heat sources based on a temperature detected by the sensor;
Using a multi-eye thermopile array as the sensor, assigning a plurality of sensing elements of the thermopile to each of the plurality of heat sources, and setting one of the plurality of sensing elements assigned to each of the heat sources, It is used to control the temperature of the heat source based on the target temperature, and the remaining sensing elements are used to detect the maximum or minimum temperature. If the detected maximum temperature exceeds the threshold value, the target temperature itself is lowered or the detected minimum A fixing device, wherein when the temperature falls below another threshold, the target temperature itself is increased. A fixing member, a plurality of heat sources for heating the fixing member, a pressure member that forms a fixing nip portion with the fixing member by pressing the fixing member, and a surface temperature of the fixing member are detected. A fixing device comprising: a sensor for controlling the plurality of heat sources based on a temperature detected by the sensor;
A multi-eye type thermopile array is used as the sensor, and a plurality of sensing elements of the thermopile are assigned to each of the plurality of heat sources, and detection indicating the highest temperature among the plurality of sensing elements assigned to each heat source If the value exceeds the threshold value set near the heat resistance temperature of the fixing member, the control temperature itself is lowered so that the minimum temperature in the recording material conveyance area does not fall below the lower limit of the fixing good range, and the temperature control of the heat source is performed. A fixing device, wherein:   The heat source comprises a central region heat source for heating the longitudinal central region of the fixing member and an end region heat source for heating the longitudinal end region of the fixing member, and the end region heat source is The fixing members are integrally formed so as to have a pair of heating regions for heating both ends of the fixing member, and the plurality of detection elements of the thermopile array are arranged in a heating region on one side of the heat source for the central region and the heat source for the end region. The fixing device according to claim 1, wherein the fixing device is assigned.   The fixing device according to claim 1, wherein the thermopile array is configured to detect a temperature by switching a plurality of detection elements with a single arithmetic circuit.   The thermopile array has a supply power cut-off circuit that cuts off power to a heat source when detecting a high temperature above a predetermined level, and a single supply power cut-off circuit corresponds to a plurality of detection elements. The fixing device according to any one of claims 1 to 4.   An image forming apparatus comprising the fixing device according to claim 1.   The image forming apparatus according to claim 6, wherein the thermopile array is disposed on a main body side of the image forming apparatus, and remains in the main body of the image forming apparatus when the fixing device is removed.   The image forming apparatus according to claim 7, wherein a measurement window is provided in a cover of the fixing device, and a shutter mechanism that closes the measurement window when the fixing device is removed is provided in the fixing device.

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