JPH07117890A - Sheet thickness detector - Google Patents

Abstract

PURPOSE:To detect the thickness of various types of sheets accurately by computing the thickness of a recording material based on a signal of strength corresponding to a change in a shaft-to-shaft distance between a pair of rotating elements which clamp a sheet. CONSTITUTION:A pair of rollers 1, 2 rotate at a circumferential speed which is equal to a conveyance speed for a recording material. The inter-shaft distance between the pair of rollers which clamp the recording material 13 increases by the amount of a thickness of the recording material. As the pair of rollers rotate, the inter-shaft distance varies from one moment to another under the influence of the eccentricity of the pair of rollers. At that time, the conveying roller 1 and the pressurizing roller 2 are engaged with each other via gears 3, 4, and a cyclic waveform is outputted by a sensor 10 to a CPU 9. An output from a reflection type photo sensor 8 which is mounted on the supporting member 6 of the conveying roller 1 is digital-signalized and sent to the CPU 9 by an AD converter 15. The CPU 9 computes the output values of the sensors 8, 10 by averaging data based on the detected values of the sensors, and determines the thickness of the recording paper by comparing it with a voltage value obtained when the pair of roller clamp a recording material of specific thickness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus or an ink jet type apparatus in which various conditions for forming an image need to be optimized according to the thickness of a sheet as a recording material for forming an image. The present invention relates to a sheet thickness detecting device that can be suitably applied to an image forming apparatus and the like.

[0002]

2. Description of the Related Art In recent years, image forming techniques such as electrophotography and ink jet have been developed, and devices capable of full-color image formation have become widespread. On the other hand, on the recording material side, various types have been developed to form a wider variety of images.

Particularly, in a color image forming apparatus, since high quality images can be obtained by recording on thick paper, it is required to form images corresponding to recording materials of various thicknesses.

However, it is necessary to optimize various conditions at the time of image formation in order to maintain the image quality while dealing with recording materials of various thicknesses.

For example, in a fixing process in which toner transferred onto an electrophotographic recording material is heated, pressurized, melted, and fixed, the amount of heat required differs depending on whether the recording material is thin or thick. It is necessary to control the temperature during fixing according to the thickness of the material.

Further, even if the recording materials of the same material have different thicknesses, the volume resistance values also differ. Therefore, in order to obtain a uniform image, the transfer current for driving the transfer charger also depends on the thickness of the recording material in the transfer process. It is necessary to change accordingly.

On the other hand, in the ink jet recording system, the distance between the recording head and the recording material has a great influence on the image quality. In order to always maintain a constant image quality, it is necessary to keep the distance between the surface of the recording material and the recording head constant regardless of the thickness of the recording material.

Further, since the image formation is performed by the serial scan system, it is necessary to intermittently convey the recording material accurately in an amount equal to the recording width. However, when the rotation angle of the conveying roller is constant, the recording material is The conveyance amount of the recording material changes depending on the thickness.

In order to solve the above-mentioned problems, an image forming apparatus having means for detecting the thickness of a recording material has been developed in recent years.

Conventionally, the mechanism shown in FIG. 7 has been often used to detect the thickness of the recording material.

That is, an actuator 61 rotatably supported by a shaft 61a is arranged in a recording material conveying path constituted by conveying roller pairs 63 and 64, a conveying guide 67, and conveying roller pairs 65 and 66. The coil spring 68 urges the actuator 68 to rotate clockwise. The conveying guide 6 is formed by the conveying roller pairs 63 and 64.
The tip of the recording material conveyed in the direction of the arrow 7 pushes up the actuator 61 to rotate it counterclockwise, and the rotation is detected by the reflection type photo sensor 62 to detect the thickness of the recording material.

Since this method has a simple mechanism and does not directly sense the paper, it can easily detect a colored recording material or a transparent recording material such as OHP.
Further, there is an advantage that the paper thickness can be amplified and detected by changing the ratio of the distance (A) from the fulcrum to the recording material and the distance (a) to the sensor 62.

[0013]

However, in the above-mentioned conventional example, it is difficult to detect the thickness of a wide variety of recording materials. For example, it is necessary to minimize the urging pressure of the actuator in order to cope with a thin recording material. However, it is difficult to detect the thickness of a relatively thick recording material in a curled state in such a state. When the urging pressure is increased to suppress the curl, it becomes difficult to convey a thin recording material.

In order to improve this point, a method of determining the thickness of the recording material by forming a pair of rollers for nipping and conveying the recording material and detecting a change in axial distance between the rollers.

As a method for measuring the distance between the shafts, a distance from a member integrally supported with one roller to a member integrally supported with the other roller is measured by a gap sensor, or a more inexpensive method. As a method, a reflection type photo sensor is mounted on a member integrally supported with one roller, infrared light is applied to the member integrally supported with the other roller, and reflected light changes according to the distance. There is a method of measuring.

[0016]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks, and an object of the present invention is to provide a sheet thickness detecting device capable of accurately detecting the thickness of a wide variety of sheets.

According to the structure for achieving the above-mentioned object, a pair of rotating bodies for sandwiching a sheet, a detecting means for emitting a signal having a strength corresponding to a change in the axial distance of the pair of rotating bodies, and a signal for the detecting means are provided. And a calculation unit that calculates the thickness of the recording material.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic view of a detecting section for detecting the thickness of a sheet as a recording material of an image forming apparatus which best represents the present invention. FIG. 2 shows a flowchart showing the operation in this case.

In FIG. 1, 1 and 2 are a pair of rollers for sandwiching and carrying a recording material, 1 is a carrying roller, and 2 is a pressure roller. Reference numeral 10 denotes a transmissive photosensor arranged upstream of the pair of rollers in the recording material conveyance direction, and detects the leading end of the recording material by blocking the optical path of the recording material. Each of the roller pairs 1 and 2 has gears 3 and 4 attached to the shaft ends thereof so as to rotate integrally with the rollers. Since the pitch circle diameter of the gear is substantially equal to the outer diameter of each roller, they mesh with each other and the phase relationship in the rotation direction of each roller is always constant. The advantage that the phase relationship is constant is related to the operation when detecting the thickness of the recording material, and will be described later.
The gear 3 is provided with a drive source 5 such as a motor for driving the rollers 1, 2. The rollers 1 and 2 are supported by a support member 6 via a bearing 14,
In particular, the pressure roller 2 is supported so as to be movable only in the direction of the arrow a, and both ends of the pressure roller 2 are urged by springs 7 in a direction in which the pressure roller 2 is pressed against the transport roller 1. Both rollers are made of metal to prevent deformation. Further, when the recording material is held by the rollers, the eccentricity of the roller pair causes an error during measurement, and therefore it is necessary to process the recording material with extremely high accuracy. For example, when each roller is eccentric by 20 μm, it is difficult to distinguish between 100 μ and 200 μ recording materials because the axial distance of both rollers when forming a roller pair changes by ± 40 μm depending on the phase. Because.

A reflection type photo sensor 8 is attached to the supporting member 6 of the conveying roller 1. The sensor 8 emits infrared light toward the shaft end of the pressure roller 2 with a light emitting element and receives the reflected light reflected by the same portion with a light receiving element, thereby outputting a voltage according to the amount of reflected light. in this case,
An output voltage approximately proportional to the distance between the pair of rollers is obtained from the sensor. However, when trying to measure the displacement of a cylindrical object such as a roller, the sensor installation error affects the measured value. Increasing the diameter of the roller in order to reduce the curvature of the roller leads to an increase in the size of the device, which is not preferable. Therefore, when the sensor has a light emitting element and a light receiving element, the light emitting element and the light receiving element are arranged in the axial direction.
The output from the sensor is converted into a digital signal by the AD converter (15) and then sent to the central processing unit (CPU) 9.

Now, the operation for actually detecting the thickness of the recording material with this apparatus will be described below with reference to the flowchart of FIG.

In the case of this apparatus, it is necessary to switch the image forming process depending on whether the recording material has a thickness of 150 μm or more or less. In this apparatus, the output value of the reflective photosensor when the recording material is not held between the roller pair is recorded in the memory in advance.

When the leading edge of the recording material 13 conveyed from the upstream direction shields the transmissive photosensor 10, the output of the sensor 10 changes and its arrival is detected (step S1). When the sensor 10 detects the leading edge of the sheet, it starts counting clock pulses (step S2), monitors whether a predetermined time has passed, and determines that the predetermined time has passed (step S3), at the same time, the CPU 9 turns the drive source 5 on. When driven, the roller pairs 1 and 2 start rotating at a peripheral speed equal to the conveying speed of the recording material (step S4). When the leading end of the recording material 13 reaches the roller pair, it is nipped by the roller pair and further conveyed. When the recording material 13 is nipped, the axial distance of the roller pair increases by the amount corresponding to the thickness of the recording material, but the distance changes with the rotation of the roller pair due to the eccentricity of the roller pair. . However, as described above, since the transport roller 1 and the pressure roller 2 are meshed with each other by the gears 3 and 4, a periodic waveform is output from the sensor 10 as shown in FIG.

Therefore, if data is fetched every rotation cycle T1 or half cycle T2 or quarter cycle T3 of the roller, even if the eccentricity of the roller pair is 10 μ, the roller can be processed by the averaging process described below. It is possible to calculate the output value of the sensor that is not affected by the size of the eccentricity of the pair.

The recording material 13 is the sensor 1 on the upstream side of the roller.
The roller pair starts rotating from the time when it reaches 0,
After a certain time (T) sufficient for the sheet to be nipped by the roller pairs 1 and 2 from the time when the rotation is started, data is stored in the memory every T1, T2 or T3 (step S8). When the number of data points reaches a predetermined number stored in advance, the data is added and divided by the predetermined number to calculate an average value (step S9), which is stored in the memory. Then, the value stored in advance in the memory (the value before the recording material is held between the roller pair) is subtracted. Then, the thickness of the recording material is determined by comparing it with the voltage value stored in the memory when the roller pair sandwiches the recording material of 150 μ (step S10).

(Other Embodiment 1) 1 for detecting the paper thickness
The use of a pair of metal rollers is described. However, it is not preferable to add this roller pair to the image forming apparatus because the apparatus becomes large. As a remedy, it is conceivable to change the roller pair that has been used so far to a configuration that can detect the paper thickness.

Now, in order to pass the paper of various thicknesses through the image forming apparatus, as shown in FIG.
A pull-out roller pair is placed in front of the. It is composed of a conveyance roller 41 and a pressure roller 42. Usually, the conveyance roller 41 is an elastic body and the pressure roller 42 is a rigid body. With this configuration, the pressure roller side is distorted and the paper thickness cannot be accurately detected.

Therefore, as shown in FIG. 5, the transport roller is constructed by combining an elastic body and a rigid body. A roller corresponding to the normal carrying roller in FIG. 4 is divided into three parts in the longitudinal direction, the portions 51 on both sides are made of an elastic body, and the central portion 52 is made of a rigid body.

Although the diameter of the elastic body portion 51 is made slightly larger than the diameter of the rigid body portion 52, since the elastic body portion is deformed, the rigid body portion 52 is in contact with the pressure roller 42 and the recording material. A conveying force is applied to the sheet to move it by the thickness of the recording material passing through.

FIG. 6 shows an embodiment using a driven roller. 5
Reference numeral 3 is a driven roller using POM having a good slipperiness.
Is a pressure spring. This structure has improved transportability.

(Other Embodiment 2) In the above-mentioned embodiment, the case where the reflection type photo sensor is used is described. However, even if another method such as a gap sensor or a PSD element (position detecting element) is used, the present invention can be applied. Do not exceed the bill. In this embodiment, an embodiment using diffused reflection light will be described.

If the roller is a roller whose surface is polished, specular reflection occurs and the performance of the sensor cannot be exhibited. Therefore, in this embodiment, a sandblasted roller is used. In consideration of durability, the surface of the sandblast was made of abrasive grains 300.

Also, the object of using a white material as the object suitable for the irregular reflection does not exceed the claim of the present patent. Specifically, there are white painted rollers and polo acetal.

[0034]

According to the image forming apparatus to which the present invention is applied, the thickness of the recording material can be detected with high accuracy regardless of the parts accuracy. Further, it is possible to cope with recording materials having a wide range of thickness, and further, it is possible to detect the thickness without being affected by the amount of curl and the like, without contaminating the recording surface of the recording material.

Especially when the roller pairs are connected by a pair of gears having a pitch circle diameter equal to the outer diameter of each roller, the detection accuracy does not depend on the eccentricity of the rollers at all, so it is not necessary to process the parts with high accuracy. A means for detecting the thickness of the recording material can be constructed at low cost.

Further, the distance between the roller pair may be affected by the disturbance due to a shock when the recording material is nipped by the roller pair. However, as described in the present invention, the thickness of the recording material is detected. By arranging the pair of rollers and the sensor for detecting that the recording material has reached the same portion, it is possible to detect the thickness of the recording material without being affected by these.

[Brief description of drawings]

FIG. 1 is a perspective view of a recording material thickness detection unit of an image forming apparatus that best represents the present invention.

FIG. 2 is a flowchart showing the operation of the embodiment.

FIG. 3 is an output waveform of a sensor.

FIG. 4 is a conventional configuration.

FIG. 5 is a schematic diagram illustrating a second embodiment.

FIG. 6 is a schematic diagram illustrating a second embodiment.

FIG. 7 shows a conventional method for detecting paper thickness.

[Explanation of symbols]

 1 Transport Roller 2 Pressure Roller 3 Gear 4 Gear 7 Spring 8 Photo Sensor 9 Central Processing Unit (CPU) 10 Photo Sensor 14 Bearing

Claims (7)

[Claims] 1. A pair of rotating bodies that sandwich a sheet, a detecting unit that detects an axial distance between the pair of rotating bodies, and a calculating unit that calculates the thickness of a recording material according to a signal from the detecting unit. A sheet thickness detection device having. 2. The sheet thickness detecting device according to claim 1, wherein one rotating body of the rotating body pair is made of a composite material of an elastic member and a rigid body. 3. The sheet thickness detecting device according to claim 1, wherein both of the pair of rotating bodies are driven by a drive source. 4. The sheet thickness detecting device according to claim 1, wherein the detecting means is arranged on the upstream side of the image forming means for forming an image on the sheet sandwiched by the pair of rotating bodies. An image forming apparatus having. 5. A photosensor having a light-emitting element for irradiating one of the rotating bodies with light, and a photoelectric conversion element for receiving electric light from the light-emitting element and reflected light from the rotating body to emit an electric signal. The sheet thickness detecting device according to claim 1, further comprising: 6. The sheet thickness detecting device according to claim 5, wherein the surface of the rotating body irradiated with light is blasted or a white material is used. 7. The sheet thickness detecting device according to claim 5, wherein the light emitting element and the photoelectric conversion element are arranged side by side in the axial direction of the rotating body.