JPH0934315A - Picture forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a good picture with a picture forming condition in accordance with the thickness of a recording member by accurately detecting thickness of the recording member even when a different picture forming device is used or parts relating to detecting thickness is changed, by giving a compensating means to a thickness detecting section. SOLUTION: N sheets of recording members A are pressed through between rollers 2 and 3, and thickness is detected by a photosensor 13. A representative value AAVE=(A1 +A2 +...+AN)/N is obtained by averaging their thicknesses. An initial value AM of the recording members is previously stored in a memory. Since an actual detected value is AAVE, compensation is required. A compensation value becomes HA=AAVE/AM. compensation values HB=BAVE/BM, HC=CAVE/ CM, HD=DAVE/DM are calculated for also recording members B, C, D having different thickness in the same way. From these compensation values, average compensation value HO=(HA+HB+HC+DO)/4 is obtained. When reciprocal of this average compensation value HO is multiplied by a detected value of thickness of a recording member, a detected value can be compensated. Highly accurate detecting thickness can be performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic or inkjet image forming apparatus.

[0002]

2. Description of the Related Art In recent years, recording materials used for image formation have been diversified in electrophotographic recording type and ink jet recording type image forming apparatuses. In particular, in a full-color image forming apparatus, the quality of an image may be subtly influenced by the thickness of the recording material, such that a higher quality image can be obtained when the recording material is appropriately thick. It is required to form an image on a recording material having the same thickness.

If the thickness of the recording material is different, the image forming condition for realizing high image quality is also changed accordingly.

For example, in the case of the electrophotographic recording method, generally, in the fixing process, the toner transferred onto the recording material is heated and pressed to be melted and fixed, and finally fixed, but this fixing is required. Since the amount of heat applied varies depending on whether the recording material is thick or thin, it is necessary to appropriately control the temperature during fixing according to the thickness. In addition, even if the recording materials of the same material have different volume resistance values when the thicknesses differ, in order to obtain a uniform image, the transfer current for driving the transfer charger should be adjusted according to the thickness of the recording materials in the transfer process. Need to be changed.

On the other hand, in the case of the ink jet recording system, in the image recording section, 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 recording head and the surface of the recording material constant regardless of the thickness of the recording material. Also,
Since the image formation is performed by the serial scan method, it is necessary to convey the recording material accurately in an amount equal to the recording width intermittently. However, if the rotation angle of the conveying roller is constant, the recording material may be changed depending on the thickness of the recording material. The conveyance amount of the recording material changes.

As described above, the image forming conditions for forming a good image, that is, the fixing temperature, the transfer current, the distance between the recording head and the recording material, the conveyance amount of the recording material, and the like are determined by the thickness of the recording material. Since it varies subtly with each other, it is an important technique to accurately detect the thickness of the recording material in order to set the optimum image forming condition.

Conventionally, a mechanism as shown in FIG. 6 has been widely used as a mechanism for detecting the thickness of the recording material.

That is, the actuator 101 is set to the fulcrum 1
01a is swingably supported and its detection side 10
By pulling 2b with the compression spring 102, the contact side 102c is lightly contacted with the conveyance guide 103. When the conveyed recording material enters between the conveyance guide 103 and the contact side 102c, the recording side 10 is detected according to its thickness.
2b moves. The thickness of the recording material is detected by detecting the amount of movement by the photo sensor 105.

This method has a simple mechanism itself, and
The thickness of a transparent recording material such as a colored recording material or an OHP sheet can be easily detected, unlike the method of directly irradiating the recording material with light to detect the thickness. . Further, the length of the contact side 102c (the distance from the fulcrum 101a to the contact portion) Y and the length of the detection side 102b (the fulcrum 10
There is an advantage that the paper thickness can be amplified and detected by changing the ratio of (distance 1a to the sensor detection position) y.

The mechanism shown in FIG. 1 is also frequently used. That is, the recording material P is nipped by the fixedly arranged conveying roller 2 and the movable pressure roller 3, and the movement amount of the pressure roller 3 at that time is detected by the photo sensor 13.

Regarding the relationship between the detected value and the thickness of the recording material by the mechanism of FIG. 6 described above and by the mechanism of FIG. 1 described above, the detected value increases as the thickness of the recording material increases. One of the relationships is such that the detected value decreases as the thickness of the recording material increases.

Here, in the case of and the thickness is A <B
A method of discriminating the recording materials having the relationship of <C <D will be described. FIG. 4 shows the relationship between these thicknesses and detected values. In the figure, the discriminant values a, b and c are set in the middle of the values corresponding to the respective detected values of the thicknesses A, B, C and D. As a result, a recording material having a detected value less than a is determined to be a recording material having a thickness A, a recording material having a thickness of B or more and less than b, and a recording material having a thickness of b or more c
A recording material having a thickness of less than C is discriminated from a recording material having a thickness of C, and a recording material having a thickness of c or more is discriminated from having a thickness of D. With this method, the thickness of the recording material can be accurately detected, and the optimum image forming condition can be set according to the detection result.

[0013]

However, according to the above-described thickness detecting mechanism and method, the photosensors 105 and 1 are provided.
As shown in FIG. 5, the relationship between the value of the detection signal and the thickness of the recording material greatly differs due to the sensitivity of No. 3, the variation of the sensitivity of the amplifier, the variation of the accuracy of the mechanical parts, and the like. For example,
As shown in the figure, a recording material whose characteristic h of the image forming apparatus H is determined to be the thickness C is determined to be the thickness D of the characteristic i of the image forming apparatus I. For this reason, even if the same recording material is conveyed, the determination of the recording material differs depending on the image forming apparatus.

The same problem occurs when the image forming apparatus is the same and the parts related to the thickness detection of the recording material such as the photo sensor, the amplifier, and the thickness detection mechanism are replaced.

In order to solve this problem, a method of reducing the variation in sensor sensitivity, the variation in amplifier sensitivity, and the variation in precision of mechanical parts that affect the gain of the detection signal can be considered, but these unnecessarily increase the cost. Therefore, it is not a suitable method.

Therefore, according to the present invention, the thickness of the recording material can be accurately detected and a high quality image can be formed by setting a good image forming condition corresponding to the thickness, without causing a special cost increase. It is an object of the present invention to provide an image forming apparatus according to the above.

[0017]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and a series of image forming means for forming an image on a recording material and a determination on the thickness of the recording material. A thickness detecting unit that has a value and detects the thickness of the recording material based on the discriminant value, and at least one image forming unit of the image forming units based on a thickness detection signal of the thickness detecting unit. Control means for changing the image forming conditions in the means,
And the thickness detecting means includes a correcting means for correcting at least one of the discriminant value and the detection signal.

The correction means conveys the recording material to be discriminated, and corrects at least one of the discrimination value and the thickness detection signal based on the thickness detection signal of the thickness detection means at this time. can do.

Further, the correction means conveys a plurality of recording materials to be discriminated, obtains a thickness detection signal corresponding to the thickness of these recording materials, and obtains an average value corresponding to the thickness of each recording material. Then, the discriminant value can be corrected by obtaining the discriminant value between the average values of the respective recording materials and replacing the discriminant value with the default discriminant value.

In addition, the correction means conveys a plurality of recording materials to be discriminated, obtains a thickness detection signal corresponding to the thickness of these recording materials, and calculates an average value corresponding to the thickness of each recording material. Then, the default value corresponding to the thickness of each recording material can be calculated from the average value of the thickness of the recording material to correct the thickness detection signal.

Next, the correcting means conveys one kind of recording material to be discriminated or a jig having a known thickness, and based on the thickness detection signal of the thickness detecting means, the discriminating value. And at least one of the thickness detection signals can be corrected.

Next, the correction means conveys one kind of a plurality of recording materials to be discriminated or a plurality of thickness jigs, obtains a thickness detection signal corresponding to the thickness, and obtains the thickness detection signal. It is possible to obtain an average value of the above values, obtain a correction value from the default value and the average value, and correct at least one of the determination value and the thickness detection signal.

[0023]

Embodiments of the present invention will be described below with reference to the drawings. <First Embodiment> FIG. 1 is a perspective view showing a schematic configuration of a thickness detecting section (thickness detecting means) 1 in an image forming apparatus according to the present invention, and FIG. 2 is a flowchart showing the operation thereof. Is.

The thickness detecting section 1 includes a pair of rollers 2 and 3 (hereinafter referred to as "each roller as appropriate") by a conveying roller 2 and a pressure roller 3 which are arranged on the lower side and the upper side so as to sandwich the conveying path of the recording material P, respectively. 2, 3 ”).

The conveying roller 2 is a side plate 5 on the left side of the supporting member 5.
It is rotatably supported by bearings 6L and 6R attached to L (the left side plate in the direction of the arrow K1 which is the conveying direction of the recording material P) and the right side plate 5R. A gear 4 is fixed to the right end side of the transport roller 2. On the other hand, the pressure roller 3 includes the left and right side plates 5L, 5R.
It is rotatably supported by bearings 7L and 7R that are vertically movable and guided by cutouts 5a and 5b, respectively. A gear 9 that meshes with the gear 4 of the transport roller 2 is fixed to the right end of the pressure roller 3. In these gears 4 and 9, the pitch circle of the gear 4 is set substantially equal to the outer diameter of the transport roller 3, and the pitch circle of the gear 9 is set substantially equal to the outer diameter of the pressure roller 3. Therefore, the phase relationship between the transport roller 2 and the pressure roller 3 is always constant. The advantage of this is related to the operation when detecting the thickness of the recording material P, and will be described later. The bearings 7L and 7R that support the pressure roller 3 are
The compression springs 10 </ b> L and 10 </ b> R are urged toward the lower conveying roller 2. As a result, the surface of the transport roller 2 and the surface of the pressure roller 3 are in contact with each other via their respective busbars. In order to prevent the deformation of the surfaces of the rollers 2 and 3 at this time, the rollers 2 and 3 are made of metal. Further, when the recording material P is nipped, the roller pairs 2 and 3 need to be processed with extremely high accuracy because the eccentricity of the rollers 2 and 3 causes an error during measurement. This is because, for example, when the rollers 2 and 3 are eccentric by 20 μm,
Depending on the phase, the maximum axial distance between the rollers 2 and 3 when forming the roller pair 2 and 3 is ± 4 depending on the phase.
This is because a change of 0 μm will occur, and if such an error occurs, it will be difficult to distinguish between the recording material P having a thickness of 100 μm and the recording material P having a thickness of 200 μm. A drive gear 12 fixed to an output shaft 11a of a motor 11 as a drive source meshes with the gear 4 of the transport roller 2.

A reflection type photo sensor 13 is attached to the upper plate (not shown) of the support member 5. The photo sensor 13 includes a light emitting element 13a and a light receiving element 13b,
Infrared light is emitted from the light emitting element 13a toward the surface of the pressure roller 2, and reflected light from the surface at this time is received by the light receiving element 13a.
By receiving at b, a voltage corresponding to the amount of reflected light is output. In this case, the photosensor 13 obtains an output voltage substantially proportional to the distance between the surface of the transport roller 2 and the surface of the pressure roller 3. However, generally, when an attempt is made 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, in the present invention,
The light emitting element 13a and the light receiving element 13b of the photo sensor 13 are arranged so as to be aligned in the axial direction of the pressure roller 3 (the generatrix direction of the surface of the pressure roller 3). By doing so, the measurement error due to the small curvature of the pressure roller 3 can be reduced. The output from the photo sensor 13 is converted into a digital signal by an AD converter (not shown),
It is sent to the CPU (central processing unit) 15. In addition, the roller pair 2 in the conveying direction of the recording material P (direction of arrow K1),
A light-transmissive photosensor 16 is arranged slightly upstream of 3. The photo sensor 16 forms an optical path that penetrates the transport path of the recording material P by a light emitting portion 16a and a light receiving portion 16b that are arranged above and below the transport path of the recording material P, and the recording material P that does not transmit light has this optical path. By cutting off, the front end of the recording material P is detected. The output from the photo sensor 16 is sent to the CPU 15 described above.

Next, the operation of actually detecting the thickness of the recording material P by the thickness detecting section 1 having the above-described structure will be described. Hereinafter, an example in which the image forming conditions are switched depending on whether the thickness of the recording material P is 150 μm or more and less than 150 μm will be described. Prior to the operation, the reflection type photo sensor 1 when the recording material P is not sandwiched by the roller pair in advance.
It is assumed that the output value of 3 is recorded in the memory.

The operation for detection is started (S1, FIG. 2).
When the recording material P is conveyed from the upstream side in the direction of the arrow K1 and the tip of the recording material P blocks the optical path of the transmissive photosensor 16, the output of the photosensor 16 changes, whereby the arrival of the recording material P is detected. (S2). The clock pulse is counted (S3), and after a lapse of a predetermined time (S4), C
The PU 15 drives the motor (driving source) 11 (S5), and the roller pairs 2 and 3 start rotating at the peripheral speed equal to the conveying speed of the recording material P. After counting for a predetermined time (S6), set the counter to 1
When the counter reaches a predetermined number of times (S7), (S7),
The leading edge of the recording material P reaches the roller pairs 2 and 3, and is nipped by the roller pairs 2 and 3 and further conveyed. When the recording material P is nipped, the axial distance between the rollers 2 and 3 increases by the amount corresponding to the thickness of the recording material P, and this is read by the photo sensor 13 (S9). The distance is sequentially changed with the rotation of the roller pairs 2 and 3 due to the eccentricity of the roller pairs 2 and 3. However, as described above, since the transport roller 2 and the pressure roller 3 are meshed with each other by the gears 4 and 9, a periodic waveform is output from the sensor 13 as shown in FIG.

Therefore, if data is taken in every rotation period T1 of the roller or half period T2 or quarter period T3,
Even if the eccentricities of the roller pairs 2 and 3 are 10 μ each, the output value of the photosensor 13 that is not affected by the eccentricity of the roller pairs 2 and 3 can be calculated by performing the averaging process described later. . The roller pairs 2 and 3 start rotating from the time when the recording material P reaches the photosensor 16 on the upstream side, but after a certain time (T) has elapsed from the time when the recording material P started, after every T1 or T2 or T3. Save the data to memory. When the number of these data reaches a predetermined number stored in advance in memory, the data is added and divided by the predetermined number to calculate an average value and stored in the memory. Then, the value stored in the memory in advance (the recording material P is the roller pair 2, 3
The value before being sandwiched by) is subtracted. This value is used as a detection value corresponding to the thickness of the recording material P.

A sequence is built in which the type of the recording material P is discriminated by comparing the detected value with the discriminant value, and the image is formed under the optimum image forming condition (process condition) for each recording material. For example, according to this detected value (S10), when the thickness of the recording material P is less than 150 μm (S11) and 150
The image forming condition is changed depending on whether or not it is more than μm (S12).

However, as described above, since the relationship between the thickness of the recording material P and the detected value differs depending on the image forming apparatus, the same image forming condition is not set even when the same recording material P is fed. There is.

Therefore, the method of adjusting the discriminant value and the method of adjusting the detected value will be described next.

There are various kinds of recording materials P that can be passed through the image forming apparatus. Among them, for example, an image forming apparatus having a specification for discriminating among four kinds of recording materials having thicknesses A, B, C and D is used. For example,

When the discriminant value adjustment key 17a on the operation unit 17 shown in FIG. 7 is pressed, the recording material having the thickness A (hereinafter referred to as "recording material A" as appropriate) is pressed.
Is input from the liquid crystal panel 17b, and the number N of sheets to be passed is input, and then N sheets of the recording material A are passed.

Next, a recording material having a thickness B from the liquid crystal panel 17b (hereinafter appropriately referred to as "recording material B", similarly recording materials having thicknesses C and D are referred to as "recording material C" and "recording material D", respectively). )
Is selected, and N sheets of recording material B are passed. The same applies to the recording materials C and D. The thickness of the recording material is stored in the memory according to the above-mentioned flow, and the _typical value of the thickness of the recording material A _AVE
Is calculated by A _AVE = (A ₁ + A ₂ + ... + A _N ) / N. Similarly for the recording materials B, C and D, B _AVE = (B ₁ + B ₂ + ... + B _N ) / N C _AVE = (C ₁ + C ₂ + ... + C _N ) / N D _AVE = (D ₁ + D ₂ + ... + D _N ) / N is calculated. Therefore, the discriminant values a, b, and c are calculated as a = (A _AVE + B _AVE ) / 2 b = (B _AVE + C _AVE ) / 2 c = (C _AVE + D _AVE ) / 2, respectively. The merit of this method is that even if the relationship between the thickness of the recording material and the detection amount of the photo sensor 13 is non-linear, it can be dealt with, and the number of passing recording materials can be selected according to the required discrimination rate. There is something you can do.

Next, the details will be described.

Since the recording materials A, B, C and D themselves also have variations, in order to accurately discriminate the thickness of the recording materials, A _AVE and B near the median of the variations of the recording materials.
_All you need is _AVE , C _AVE , and D _AVE . Therefore, if a high discrimination rate is not required, it is sufficient to pass the sheets one by one. For example, recording material 70g paper, 120g
When discriminating between paper, 170 g paper and 220 g paper, the discrimination rate was 90% when the discrimination value was determined by passing one sheet, and 99% when the discrimination value was determined by passing five sheets each.

Similarly, a method of adjusting the detected value will be described.

The discriminant value adjustment key 17a on the operation unit 17 shown in FIG. 7 is pressed, the recording material A is selected from the liquid crystal panel 17b, and the number N of sheets to be fed is input. Pass it through. Next, B, C, and D are similarly performed. The detected value corresponding to the thickness of the recording material is stored in the memory according to the flow described above, and the _typical value of the thickness of the recording material A is A _AVE = (A ₁ + A ₂ + ... + _AN ) / N, and similarly. , The representative values of the recording materials B, C and D are: B _AVE = (B ₁ + B ₂ + ... + B _N ) / N C _AVE = (C ₁ + C ₂ + ... + C _N ) / N D _AVE = It is calculated as (D ₁ + D ₂ + ... + D _N ) / N. The initial values corresponding to the recording materials A, B, C and D are stored in advance in the memory, and A _M , B
_M , C _M and D _M. Actual detection values are A _AVE and B
_{Since it is AVE} , C _AVE , and D _AVE, it is necessary to correct it.

Therefore, the correction values are set to H _A , H _B , H _C , and H _{D.
Each, H A = A AVE / A} M H B = B AVE / B M H C = C AVE / C M H D = D AVE / D determined from _M, the average correction value H ₀ H ₀ = (H _A It is calculated from + H _B + H _C + D ₀ ) / 4.

The detection value can be corrected by multiplying the detection value by the reciprocal of the average correction value H ₀ .

Then, the recording material is identified based on the corrected detection value or the discriminant value, and as described above, the image forming conditions such as the transport condition, the fixing condition and the transfer condition are changed.

Specifically, regarding the transport conditions, the thicker the recording material, the slower the transport speed, and the larger the distance between the preceding recording material and the succeeding recording material. Further, regarding the transfer condition, the transfer current is controlled or the transfer separation current is controlled to perform the transfer condition under the optimum condition for the recording material. <Embodiment 2> When the relationship between the thickness of the recording material and the detected value is substantially linear, for example, the recording materials A, B, C,
The discriminant values a, b, c for discriminating D are c = 0.75.
It can be expressed as a, b = 0.5a. Therefore,
By flowing the recording material D in the same manner as in the first embodiment, the representative value D _AVE is obtained from D _AVE = (D ₁ + D ₂ + ... + D _N ) / N, and the recording material D stored in the memory in advance. By dividing by the value D _M corresponding to
Is obtained as H = D _AVE / D _M. By multiplying the initial discriminant value by this correction value H, the discriminant value peculiar to the image forming apparatus can be obtained as follows.

A '= Ha b' = 0.5 a '= 0.5 Ha c' = 0.75 a '= 0.75 Ha Further, when the detected value is corrected with the discriminant value kept as the initial value, the thickness is detected. It suffices to divide the value by the correction value.

In the second embodiment, the correction value can be obtained from the relationship of the thickness jig of the recording material as long as the jig has a known thickness, instead of one type of recording material. The discriminant value or the detected value can be corrected. <Third Embodiment> In the first and second embodiments described above, mainly,
Although the adjustment method in the factory has been described, the adjustment performed by the user will be described in the present embodiment.

The fixing speed is an item for determining and controlling the recording material. When fixing is performed from the thin recording material to the thick recording material at the same fixing speed, the thin recording material has an image having too much gloss, while the thick recording material has an image having no gloss at all.

Therefore, as an example, the recording materials A, B, C, D
Fixing speed _{V A, V B, V C} , V D are prepared in the. However, in order to meet various requests of users, as shown in FIG.
7c is provided, and when the gloss button 17d is pressed, the discriminant values a, b, and c shift to a ', b', and c ', respectively, as shown in FIG. The same as the above, but a glossy image can be output.

Further, as an extension of this embodiment, the discriminant value can be changed depending on the environment. When the temperature and humidity are high, the recording material itself expands and becomes thicker than it should be,
Since the image is detected as being one step thicker, the image becomes too glossy. Therefore, it is possible to perform control that is not affected by the environment by changing the discriminant value according to the information of the environment sensor. <Fourth Embodiment> In the first to third embodiments described above, the method of operating the discriminant value and the gain of the detection value by using the recording material and the thickness jig has been described. Examine in advance how much the sensor, amplifier, and mechanical parts that affect the design deviate from the design values. For example, when the combination of the sensor is + 3%, the amplifier is -7%, and the mechanical part is + 5%, the discriminant values are a '= a / (1.03 × 0.93 × 1.05) b'. = A / (1.03 × 0.93 × 1.05) c ′ = a / (1.03 × 0.93 × 1.05), and when adjusting with gain, k ′ = k / (1 0.03 × 0.93 × 1.05).

This can be applied even when a part fails in the market. For example, when the sensor fails and is replaced, the service person operates the liquid crystal panel 17b of FIG. 7 to enter the service mode (not shown) (S21, see the flowchart of FIG. 9), and the replacement part selects the sensor ( S23),
For the gain, if the sensitivity attached to the sensor is input (S26), the discriminant value or the gain is reset by the above calculation method (S29). Similarly, if the component to be replaced is an amplifier, S24, S27, S30, and if it is a mechanical component, S25, S28, S31.

[0050]

As described above, according to the present invention,
Even if the image forming apparatus is different or the sensitivity or accuracy of the member or the like for detecting the thickness of the recording material varies, the thickness of the recording material can be accurately detected without increasing the cost. . Therefore, it is possible to form a good image by changing the image forming conditions according to the thickness detected with high accuracy.

[Brief description of drawings]

FIG. 1 is a perspective view showing a configuration of a recording material thickness detection unit of an image forming apparatus according to a first embodiment.

FIG. 2 is a flowchart showing the operation of the thickness detection unit according to the first embodiment.

FIG. 3 is a diagram showing an output waveform of a photo sensor when a roller forming a thickness detection unit is eccentric.

FIG. 4 is a diagram showing a relationship between a recording material thickness and a detected value.

FIG. 5 is a diagram showing a relationship between a recording material thickness and a detected value when the image forming apparatus is different.

FIG. 6 is a view showing a conventional mechanism for detecting a paper thickness.

FIG. 7 is a diagram showing various setting keys of the operation unit.

FIG. 8 is a conceptual diagram showing adjustment of a discriminant value.

FIG. 9 is a flowchart for changing a discriminant value by exchanging components related to thickness detection.

[Explanation of symbols]

 1 Thickness detecting means (thickness detecting section) 2 Conveying roller 3 Pressure roller 13, 16 Photo sensor 17 Operating section 17a Discrimination value adjustment key A, B, C, D Recording material thickness a, b, c Discrimination value

Claims (6)

[Claims] 1. A series of image forming means for forming an image on a recording material, and a thickness having a discriminant value for the thickness of the recording material and detecting the thickness of the recording material based on the discriminant value. The thickness detecting means; and a control means for changing image forming conditions in at least one of the image forming means based on a thickness detection signal of the thickness detecting means. An image forming apparatus comprising: a correction unit configured to correct at least one of the discriminant value and the detection signal. 2. The correction means conveys a recording material to be discriminated, and corrects at least one of the discrimination value and the thickness detection signal based on a thickness detection signal of the thickness detection means at this time. The image forming apparatus according to claim 1, wherein: 3. The correction means conveys a plurality of recording materials to be discriminated, obtains a thickness detection signal corresponding to the thickness of these recording materials, and obtains an average value corresponding to the thickness of each recording material. 3. The image forming apparatus according to claim 2, further comprising: determining a discriminant value between the average values of the respective recording materials and replacing the discriminant value with a default discriminant value to correct the discriminant value. 4. The correcting means conveys a plurality of recording materials to be discriminated, obtains a thickness detection signal corresponding to the thickness of these recording materials, and obtains an average value corresponding to the thickness of each recording material. The image forming apparatus according to claim 2, wherein a default value corresponding to the thickness of each recording material is obtained from a mean value of the thickness of the recording material to obtain a correction value, and the thickness detection signal is corrected. . 5. The correction means conveys one kind of recording material to be discriminated or a jig having a known thickness, and based on a thickness detection signal of the thickness detecting means, the discriminating value The image forming apparatus according to claim 1, wherein at least one of the thickness detection signals is corrected. 6. The correcting means conveys one kind of a plurality of recording materials to be discriminated or a plurality of thickness jigs, obtains a thickness detection signal corresponding to the thickness, and corresponds to the thickness. The image forming apparatus according to claim 5, wherein an average value is obtained, a correction value is obtained from the default value and the average value, and at least one of the determination value and the thickness detection signal is corrected. .