JP2001100588A - Heater and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heater which prevents a fixing defect in the latter half of paper which occurs when using a material having a high heat insulating property for a pressure roller. SOLUTION: When a material having a high heat insulating property is used for a heat insulating layer of the pressure roller, the surface temperature of the roller is lowered during paper passage, and the amount of heat supplied from the pressure roller to paper is reduced to cause a fixing defect. In order to prevent this defect, electric energy supplied to a heater as a heating body is changed synchronously with the rotation period of the pressure roller to compensate reduction of the amount of heat supplied from the pressure roller. This electric energy is determined by the variation of the detection temperature of a thermistor or the variation of power consumption at the time of entrance of paper to a nip part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using an electrophotographic process such as a copying machine, a laser printer, a facsimile, etc., and a heating apparatus for fixing a toner image carried on a recording material by heating and pressing. Things.

[0002]

2. Description of the Related Art Conventional image forming apparatuses of this type include:
For example, there is a laser printer 100 shown in FIG.

This laser printer includes a paper feeding section 102 for separating and transporting recording materials such as recording paper loaded one by one, and a laser optical system for modulating and emitting a laser beam based on image data provided from an external device. 103, an image forming unit 104 for forming an image by irradiating the laser beam described above, and a heat fixing device 1 for fixing to a recording material by supplying heat and applying pressure
05, a control device 106 for controlling the sequence of each unit and each device described above.

When image information is transferred from an external device, the paper feeding unit 106 separates recording sheets one by one from a paper feeding tray 107 and transports the recording paper to the image forming unit 104.

On the other hand, a registration sensor 118 is provided on the transport path to the image forming unit 104, and detects the leading end of the recording paper and the length of the recording paper by falling down when the recording paper passes.

[0006] The image forming section 104 has a photosensitive drum 110 as a latent image carrier rotatably supported by a shaft. The photosensitive drum 110 is uniformly rotated by a charging roller 108 also supported by a rotatable shaft. The latent image is formed by the laser beam irradiated from the laser optical system 103 which is charged and turned on / off based on the image information.

Subsequently, the photosensitive drum 1 on which the latent image is formed
The toner 10 is applied to the charged area on the surface of the photosensitive drum 110 by a bias applied between the photosensitive drum 110 and the developing sleeve 109 when passing through a position facing the developing sleeve 109 carrying the toner, A toner image is formed.

The formed toner image is transferred to the photosensitive drum 110
When the sheet passes through the contact portion between the transfer roller 111 and the transfer roller 111, the image is transferred onto a recording material by a transfer bias applied between the photosensitive drum 110 and the transfer roller 111.

The recording material carrying the toner image becomes a fixed image by applying heat and applying pressure in the heat fixing device 105, and is discharged by a discharge roller 119, thereby completing a series of image forming processes. .

Conventionally, as a heat fixing device, a roller heating system shown in FIG. 3 has been often used.

The fixing roller 20 is configured such that a roller having a heat-resistant release layer such as PFA formed on the surface of a core metal such as aluminum is heated from the inner surface by a heater 21. The heater is turned on / off by a control circuit (not shown) based on the control to maintain a predetermined temperature.

A nip portion between the fixing roller 20 and the pressure roller 23 is pressed against a paper P on which the toner image T is placed.
Passes, and the toner image T is melted and fixed.

However, this method has a problem that the fixing roller 20 cannot be used immediately unless the fixing roller 20 is kept at a high temperature and kept in a standby state because the heat capacity is large and the temperature is hard to rise.

In order to solve the problem of the roller heating system, there has been proposed a film heating system heating and fixing apparatus for applying heat from a heating body to paper through a resin film having a small heat capacity and heating the paper. It is disclosed in JP-A-63-313182, JP-A-2-157778, and the like.

This film heating type heat fixing device is
A heating element, a heating element support that supports the heating element, a film that is in close contact with the heating element,
And a pressure roller for pressing the paper against the heating body.

According to this method, since the heat capacity of the entire fixing device is small, and the paper is opposed to the heating element with only the film interposed therebetween, heat is efficiently applied to the paper, and the power consumption is small. It is possible to fix the toner.

[0017]

In the above-mentioned heat fixing apparatus of the film heating type, in order to further reduce the power consumption, a pressure roller (hereinafter referred to as a heat insulating roller) using an elastic layer with a material having high heat insulating properties. It has been proposed to use

In order to achieve both the reduction in power consumption, the further increase in speed, and the reduction in startup time,
The heat-insulating roller described above is indispensable in that heat leakage into the roller is small and the surface of the roller quickly rises in temperature.

However, when a material having a high heat insulating property is used for the pressure roller, the heat storage effect of the pressure roller is reduced, so that heat is supplied from the pressure roller to the paper to the conventional pressure roller. It is greatly reduced in comparison. As a result, in the latter half of the paper passing through the nip portion, the fixing property is likely to be deteriorated, and a problem may occur in an image.

The invention according to the present application does not require an additional member, maintains the energy-saving effect by using a roller having a high heat insulation property, and prevents image defects (hot offset) due to poor fixing and excessive melting of toner. It is an object of the present invention to provide a heating device and an image forming apparatus capable of obtaining a stable and stable fixed image.

[0021]

According to a first aspect of the present invention, there is provided a heating apparatus having a heating member having a heating element which generates heat and a roller-like member for bringing a recording material into close contact with the heating member. A pressurizing member having a rotating heat insulating layer, and control means for controlling energization of the heating element, and recording is performed by conveying a recording material through a nip formed by the heating member and the pressurizing member. In a heating device for heating a material, the control means changes electric power supplied to the heating element in accordance with a rotation cycle of the pressing member.

A second configuration of the heating apparatus for realizing the object of the invention according to the present application includes a heating member having a heating element that generates heat and a roller-shaped rotating heat insulating layer for bringing a recording material into close contact with the heating member. A heating device having a pressure member having a control means for controlling energization of the heating element, and heating the recording material by conveying the recording material through a nip formed by the heating member and the pressure member Wherein the control means changes a control temperature of the heating element in accordance with a rotation cycle of the pressing member.

A third configuration of the heating device for realizing the object of the present invention according to the present application is the first configuration, wherein the control means controls the temperature of the heating element before and after the recording material enters the nip portion. Based on the change in the detected temperature of the temperature detector that detects
The electric power is changed every rotation cycle of the pressing member.

A fourth configuration of the heating device for realizing the object of the invention according to the present application is the second configuration, wherein the control means controls the temperature of the heating element before and after the recording material enters the nip portion. Based on the change in the detected temperature of the temperature detector that detects
The control temperature is changed every rotation cycle of the pressing member.

A fifth configuration of the heating apparatus for realizing the object of the invention according to the present application is the above-mentioned first configuration, wherein the control unit controls the heating element before and after the recording material enters the nip portion. The power is changed every rotation cycle of the pressurizing member based on a change in the power.

A sixth configuration of the heating device for realizing the object of the invention according to the present application is the second configuration, wherein the control means controls the heating unit before and after the recording material enters the nip portion. The control temperature is changed every rotation cycle of the pressurizing member based on a change in electric power.

According to a seventh aspect of the heating device for realizing the object of the present invention according to the present invention, the thermal conductivity of the heat insulating layer of the pressing member is 1.0 × 10 ^-4 to 3.0 × 1
0 ^-4 [cal / cm · sec · ° C].

An eighth configuration of the heating device for realizing the object of the invention according to the present application is the above-described first, third, fifth or seventh configuration, wherein the control means increases the electric energy. It is characterized by changing.

A ninth configuration of the heating apparatus for realizing the object of the invention according to the present application is the second, fourth, sixth or seventh configuration, wherein the control means increases the control temperature. It is characterized by changing.

An image forming apparatus for realizing the object of the invention according to the present application includes a latent image carrier on which a latent image is formed, and a recording material for forming a toner image on the latent image carrier developed by developing means. And a fixing unit for fixing the toner image transferred to the recording material by the transfer unit by applying heat and pressure. The heating unit having any one of the above-described configurations is used as the fixing unit. It is characterized by the following.

In the heating device having the above-described structure, a material having high heat insulating properties is used for the pressure roller as the pressure member, and even when the supply of heat from the pressure roller to the paper is reduced, the heating member is not heated. Since the control is such that the amount of heat generation is increased, heat can be uniformly supplied over the entire surface of the paper, and a stable and good fixing device can be provided.

In addition, the pressure roller is made of a material having a high heat insulating property, and the control temperature of the heating element is increased even when the supply of heat from the pressure roller to the paper decreases. As a result, heat can be uniformly supplied over the entire surface of the paper, and a stable and favorable fixing device can be provided.

Further, the thermal conductivity of the heat insulating layer is set to 1.0 × 1
With the configuration of 0 ^{-4 to} 3.0 × 10 ^-4 [cal / cm · sec · ° C.], the power supplied to the heating element is increased, so that it is always stable and has good fixability over the entire surface of the paper. Equipment can be provided.

Further, by controlling the addition of power or raising the control temperature on the basis of the temperature change of the temperature detecting element or the power change to the heating element, it is possible to always secure good fixability over the entire surface of the paper. In addition, the start-up time and power consumption can be reduced.

In the above-described image forming apparatus, the start-up time can be reduced, the power consumption can be reduced, and good fixability can be ensured.

[0036]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) FIGS. 1, 2, and 4 to 6 show a first embodiment of the present invention.

The heating and fixing apparatus shown in FIG. 1 to which the present invention is applied includes a heating member 1, a substantially semi-cylindrical heating member supporting member 4 for supporting the heating member 1, a heating member 1 and a heating member supporting member 4. And a pressure roller 5 that forms a nip with the heat-resistant film interposed between the heat-resistant film 3 and the heating element 1.

Here, the film 3 has an inner peripheral length fitted to the outer periphery of the heater 1 and the heater support 4 with a margin. Therefore, the film 3 rotates while being guided by the heating body 1 and the heating support 4.

The film 3 has a thickness of 20 to 100 μm.
And a release layer made of a fluororesin such as PTFE and PFA provided on the substrate.

The heating element 1 is made of a heat-resistant insulating substrate of good heat conductivity such as alumina and, for example, Ag / Pd (silver palladium) coated on the surface of the substrate by screen printing or the like.
About 10 μm thick and 1 to 3 widths made of an electric resistance material
It has an electrical resistance layer of mm and a protective layer made of glass, fluororesin or the like coated on the electrical resistance layer.

The pressure roller 5 is composed of a metal core 5a and a heat-resistant elastic layer 5b provided around the metal core 5a.

By using a material having a high heat insulating property and a small heat capacity for the elastic layer 5b, the heat fixing device can immediately start the fixing operation even when the power is off.

The pressure roller 5 has a function of pressing the paper P against the heating element 1 via the film 3 and driving the film 3.

The heating element 1 has a thermistor 2 on its surface as a temperature detecting means. This thermistor 2
As shown in FIG. 2, it is connected to a CPU 10 as a temperature control means via an A / D converter 11.

Further, the CPU 10
The power supply to the heating element 1 is controlled via the. This energization control is performed, for example, by controlling the phase or the wave number of the AC voltage. That is, CPU1
0 is output from the thermistor 2 and A / D converter 11 outputs A
Based on the temperature information signals of the pressure roller 5 and the heating element 1 that have been subjected to the / D conversion, the triac 12 controls the energization of the heating element 1.

The CPU 10 according to the present embodiment performs control for additionally supplying power in accordance with the rotation cycle of the pressure roller 5.

In this control, as described below, as a result of forming the pressure roller 5 with a material having a low thermal conductivity, the heat capacity is also reduced at the same time, so that the supply of heat from the pressure roller to the paper is reduced. It complements that.

The thermal conductivity conventionally used is about 6.0 × 1
Using a pressure roller of 0 ^-4 [cal / cm · sec · ° C.], the temperature change of the roller surface when the paper was passed through the fixing device was measured, and the surface temperature was as shown in FIG. changed. With the conventional pressure roller having such a certain heat capacity, the surface temperature does not drop significantly.

On the other hand, when the temperature change of the roller surface was similarly measured using a pressure roller (insulated roller) formed of a material having a low thermal conductivity, the temperature decreased stepwise as shown in FIG.

When the surface temperature of the pressure roller decreases as described above, the supply of heat from the pressure roller to the paper decreases.
Fixing property is deteriorated.

The deterioration of the fixing property is caused by the fact that the thermal conductivity of the elastic material used for the elastic layer of the pressure roller is 3.0 × 10 ⁻⁴ [ca
l / cm · sec · ° C.] or less, the image becomes noticeable as a fixing defect in the image. Therefore, in the present embodiment, the power supplied to the heating element during paper passing is increased by every rotation of the pressure roller. Control is performed to secure the fixing property.

On the other hand, even when the thermal conductivity of the elastic layer of the pressure roller is 1.0 × 10 ⁻⁴ [cal / cm · sec · ° C.] or less, additional power is additionally supplied to secure the fixing property. However, the toner on the paper was overmelted and adhered to the film 3, and a good image was not obtained.

That is, it is possible to control the fixing power by increasing the energizing power with respect to the change in the thermal conductivity of the pressure roller substantially, at 1.0 × 10 ⁻⁴ [cal / cm · sec.・ ℃]
It is within the range of ~ 3.0 × 10 ^-4 [cal / cm · sec · ° C.].

Actually, using the heat fixing device having the configuration of the present embodiment, the temperature of the heat fixing device is controlled at a constant temperature of 195 ° C. from a normal temperature state for LTR size paper having a basis weight of 90 g / m ^2. When the image output was performed, the density reduction rate distribution as shown in FIG. 5 was found in one sheet of paper.
Here, the density reduction rate is an index for evaluating the quality of fixability based on a change in image density when an image is rubbed with a predetermined pressure, and is defined by the following equation.

Density reduction rate = (image density before rubbing−image density after rubbing) / image density before rubbing × 100 [%] As can be seen from the above equation, the lower the density reduction rate, the better the fixability. That is, it can be seen that when an image is output at a constant temperature control of 195 ° C., the fixing property decreases with the outer diameter cycle of the pressure roller.

On the other hand, an image was output in the same manner using the control of the present embodiment in which the power supplied to the heating element was increased by 20 [W] every time the pressure roller circulated. In the heat fixing device of the present embodiment, since the paper conveyance speed is 76.0 [mm / s] and the diameter of the pressure roller is 20.0 [mm], (20 × π) [mm] / 76 [mm / 0.827 [s] from 0.827 [s] after the paper enters the nip of the heat fixing unit
Control to increase the power every time.

FIG. 7 is a flowchart showing the control of this embodiment.

In FIG. 7, t indicates the time that has elapsed since the paper entered the fixing device.
Each time, 20 W of power is added.
Also, since the length of the LTR paper is 279 [mm], [279 [mm]
If / 76 [mm / s] or [s] has elapsed, the paper has been discharged from the fixing device, and printing is completed.

When an image was actually output using the control of the present embodiment, the density reduction rate distribution shown in FIG. 6 was obtained, and the fixing property was improved, and good fixing property was obtained over the entire area of the paper. I knew it was. When the image forming apparatus using the heating device is used in a low-temperature environment, the fixing property is more significantly reduced, and the control of the present embodiment is effective.

Further, in the present embodiment, the heat fixing device of the film heating type has been described as an example, but the present invention can be similarly applied to the heat fixing device of the roller heating type. (Second Embodiment) In the above-described first embodiment, the electric power to be supplied to the heating element is changed according to the rotation cycle of the pressure roller. However, in the second embodiment, The control temperature of the heating element was changed.

That is, by increasing the control temperature of the heating element in accordance with the rotation cycle of the pressure roller, the shortage of the amount of heat required for fixing is compensated, and a stable fixed image output is obtained.

For example, after the second rotation of the pressure roller, a comparison was made with the conventional control in the same manner as in the first embodiment, using a heat fixing device in which the control temperature was increased by 5 ° C.

As a result, in the conventional control, the distribution of the density reduction rate was as shown in FIG. 5, but by using the control of the present embodiment, similar to the first embodiment, over the entire area of the paper. It was found that good fixability was obtained.

The control of the present embodiment is particularly effective for reducing the fixability in a low-temperature environment, as in the first embodiment.

(Third Embodiment) In the present embodiment,
The control temperature described in the second embodiment is changed based on the temperature change detected by the thermistor when the paper enters the fixing device.

In the heat fixing device of this embodiment, paper
Is constant temperature T₁ Into the heat-fixing unit controlled by
The paper loses heat, so it is installed on the surface of the heating element.
The temperature detected by the thermistor is T as shown in FIG._X Ma
It temporarily drops. This T ₁ And T_X Calculated as the difference between
The amount of reduction ΔT depends on the basis weight of the paper or the temperature of the paper.
When the weight is large or when the paper temperature is low.
In that case, it gets bigger because it takes more heat.

That is, since the amount of power shortage after the second rotation of the pressure roller can be predicted from the magnitude of the decrease amount ΔT, the amount of power to be additionally supplied after the second rotation is determined.

FIG. 9 is a flowchart showing the control of this embodiment.

[0069] That is, the heating fixing device temperature control is performed at the initial control temperature T _1, the paper detects the temperature T _X which is temporarily lowered at the time of entered the fuser.
Thereby, the temperature decrease amount ΔT at the thermistor position due to the paper entry is calculated. Since the magnitude of the reduction amount ΔT reflects the basis weight of the paper, the temperature of the paper, and the like, it is possible to predict insufficient power after the second rotation of the pressure roller.

For example, when ΔT is 5 deg. If it is less than 1, the amount of heat deficient after the second rotation of the pressure roller is expected to be small, so the temperature control temperature after the first week of the pressure roller is set to T ₁ +3 [° C.]. On the other hand, ΔT is 15d
eg. When the temperature exceeds T _1, it is predicted that the heat quantity will be significantly short after the second rotation of the pressure roller, so the temperature regulation temperature is set to T _1.
+10 [° C], and T ₁ +
Fixing is performed at a temperature control temperature of 10 ° C.

As a result, it is possible to deal with paper basis weights and the like that could not be achieved in the first and second embodiments, and papers having different basis weights (52.3, 75, 90, 105 g / m As a result of performing the fixing operation for ² ), an image having good fixability was obtained over the entire surface of paper having all basis weights.

In this embodiment, the case where the temperature adjustment temperature is changed after the second rotation of the pressure roller has been described. However, by repeating the same procedure, the temperature adjustment temperature is changed for each rotation of the pressure roller. It can be changed.

Further, the case where the control temperature is changed based on ΔT has been described.
Needless to say, the same effect can be obtained by changing the electric energy as in the embodiment. (Fourth Embodiment) In the above-described third embodiment, the amount of electric power to be additionally supplied in the rotation cycle of the pressure roller or the temperature change detected by the thermistor when the paper enters the fixing device. Although the control temperature to be changed is determined, in the present embodiment, these are determined from a change in the power supplied to the heating element when the paper enters a fixing device controlled at a constant temperature. It is.

That is, when the leading edge of the paper enters the heat-fixing unit controlled at a constant temperature, the heat is taken away by the paper. Therefore, the temperature detected by the thermistor installed on the surface of the heating element is the third embodiment. As described in (1), the temperature instantaneously decreases, but at the same time, the power supplied to the heating element is also increased to maintain a constant temperature.

The electric energy ΔP increased at this time also reflects the basis weight of the paper or the temperature of the paper.
The amount of power required for the second and subsequent rotations of the pressure roller can be predicted from the magnitude of the pressure roller.

Also in this embodiment, as in the third embodiment, as a result of performing a fixing operation on paper having different basis weights, an image having good fixability can be obtained on paper having all basis weights. I was able to.

Further, similarly to the third embodiment, the control temperature of the heating element can be changed based on the magnitude of the increased power amount ΔP.

[0078]

As described above, according to the present invention,
Since the amount of heat generated by the heating element is changed so that the amount of heat supplied to the paper during the fixing operation is kept constant, poor fixing, uneven fixing,
An image without hot offset can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a heat fixing device according to first to fourth embodiments of the present invention.

FIG. 2 is a block diagram illustrating a temperature control system of the heat fixing device of FIG. 1;

FIG. 3 is a schematic sectional view of a conventional heat roller type heat fixing device.

FIG. 4 is a diagram comparing changes in the surface temperature of the conventional pressure roller and the heat insulating roller used in the first embodiment during paper passing.

FIG. 5 is an LTR when an image is output using conventional control.
The figure which shows the distribution of the density reduction rate within the size.

FIG. 6 is a diagram illustrating a distribution of a density reduction rate within an LTR size when an image is output using the control of the first embodiment.

FIG. 7 is a flowchart illustrating control of the fixing device according to the first embodiment of the present invention.

FIG. 8 is a diagram illustrating a change in the thermistor detection temperature when paper enters a fixing device, detected in the third embodiment of the present invention.

FIG. 9 is a flowchart illustrating temperature control of a fixing device according to a third embodiment of the present invention.

FIG. 10 is a schematic sectional view of a conventional image forming apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Heating body 2 ... Thermistor 3 ... Film 4 ... Heating body support 5 ... Pressure roller 5a ... Core metal 5b ... Elastic layer 6 ... Thermistor 10 ... CPU 11 ... A / D converter 12 ... Triac P ... Recording material T …toner

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) H05B 3/00 335 H05B 3/00 335 (72) Inventor Satoru Taniguchi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon (72) Inventor Yusuke Nakazono 3-30-2 Shimomaruko, Ota-ku, Tokyo F-term (reference) in Canon Inc. 2H033 AA03 AA09 AA32 BB29 BE03 CA22 CA30 CA44 3K058 AA02 AA41 AA65 AA72 AA81 BA18 CA23 CA46 CA61 CB06 CB19 CB22 CD01 CE04 CE13 DA04 5H323 AA36 BB20 CA08 CB03 DA02 DB04 FF03 GG04 NN03

Claims (10)

[Claims] 1. A heating member having a heating element that generates heat when energized, a pressure member having a roller-shaped rotating heat insulating layer for bringing a recording material into close contact with the heating member, and a control unit that controls energization to the heating element. A heating device that heats the recording material by conveying the recording material through a nip formed by the heating member and the pressing member, wherein the control unit is configured to control the rotation of the pressing member in accordance with a rotation cycle of the pressing member. A heating device, wherein electric power supplied to the heating element is changed. 2. A heating member having a heating element that generates heat when energized, a pressing member having a roller-shaped rotating heat insulating layer for bringing a recording material into close contact with the heating member, and control means for controlling energization to the heating element. A heating device that heats the recording material by conveying the recording material through a nip formed by the heating member and the pressing member, wherein the control unit is configured to control the rotation of the pressing member in accordance with a rotation cycle of the pressing member. A heating device for changing a control temperature of the heating body. 3. The control device according to claim 1, wherein the control unit is configured to control an electric power for each rotation cycle of the pressure member based on a change in a temperature detected by a temperature detecting element for detecting a temperature of the heating element before and after the recording material enters the nip. The heating device according to claim 1, wherein: 4. The control means controls the pressurizing member for each rotation cycle based on a change in a detected temperature of a temperature detecting element for detecting a temperature of the heating element before and after a recording material enters a nip portion. The heating device according to claim 2, wherein the temperature is changed. 5. The method according to claim 1, wherein the control unit is configured to determine whether or not the power to the heating element changes before and after the recording material enters the nip.
The heating device according to claim 1, wherein the power is changed every rotation cycle of the pressing member. 6. The control device according to claim 1, wherein the control unit is configured to determine whether or not the recording material has entered the nip before and after the recording medium enters the nip.
The heating device according to claim 2, wherein the control temperature is changed every rotation cycle of the pressure member. 7. The thermal conductivity of the heat insulating layer of the pressure member is:
The heating device according to claim 1, wherein the heating device has a temperature of 1.0 × 10 ^{−4 to} 3.0 × 10 ⁻⁴ [cal / cm · sec · ° C.]. 8. The heating device according to claim 1, wherein the control unit changes the electric energy so as to increase the electric energy. 9. The heating device according to claim 2, wherein the control means changes the control temperature so as to increase the control temperature. 10. A latent image carrier on which a latent image is formed, transfer means for transferring a toner image formed on the latent image carrier developed by a developing means to a recording material, and transfer to a recording material by the transfer means. An image forming apparatus comprising: at least a fixing unit for fixing the formed toner image by applying heat and pressure; and using the heating device according to claim 1 as the fixing unit.