JPH06161284A - Image forming device - Google Patents

Abstract

PURPOSE:To always excellently primarily electrify an image carrier and to stably obtain a high-quality image by preventing it from being contaminated very much by contaminant from an electrifying means by causing the same position to always face to the primary electrifying means at the time of stopping because the image carrier substantially has the relation of peripheral length ratio of integer multiple to a transfer material carrier which is stopped at the same time. CONSTITUTION:A notched part 20d is provided to extend from a gripper 22 set as a home position to a downstream side in its rotating direction on the outer peripheral surface of a transfer drum 20, and a lever 31 is provided at a proximate position on the upstream side and a sensor 32 detecting passing that position by the lever 31 is provided on the outside of the drum 20. Then, the image is formed while deviating a stopping position by increasing stopping time by alpha (seconds) every rotation by beginning from the stopping at (t) (seconds) after detecting the passing. When the gripper 22 reaches the position of a photosensitive drum 1, operation is repeated from the beginning. Thus, the stopping position of the photosensitive drum 1 is deviated from that of the previous time, thereby the purpose can be achieved.

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 for transferring a plurality of color toner images formed on an image carrier onto a transfer material to obtain a color image, and more particularly to a toner image of each color on the image carrier. The present invention relates to an image forming apparatus that obtains a color image by multiple transfer in which each time a sheet is formed, it is transferred onto a transfer material wound around a transfer drum.

[0002]

2. Description of the Related Art In an image forming apparatus for obtaining a color image on a transfer material by superposing toner images of plural colors, a toner image is obtained by charging, exposing and developing on an image carrier. There is a method in which a toner image of a plurality of colors is superimposed on the transfer material to obtain a color image by repeating the step of transferring to the transfer material for each color. This type of color image forming apparatus is DAS26077.
No. 27, Japanese Patent Laid-Open No. 50-50935, etc. have been put to practical use.

FIG. 4 is a vertical sectional view showing the overall structure of the above-mentioned color image forming apparatus. As shown in the drawing, a photosensitive drum 1 is provided as an image carrier in the apparatus, and the photosensitive drum 1 is surrounded by A primary charger 3, a rotary developing device 4 having a plurality of developing devices, a transfer device 10A, and a cleaner 26 are installed. A laser diode 11, which constitutes an exposure device, a polygon mirror 13 rotated by a high-speed motor 12, a lens 14, and a folding mirror 15 are arranged above the photosensitive drum 1.

The photosensitive drum 1 comprises an aluminum cylinder having a diameter of 40 mm and a photoconductor made of an organic photoconductor (OPC) coated on the outer peripheral surface thereof. The photoconductor may be amorphous Si, CdS, Se or the like. The photosensitive drum 1 is rotated in the direction of the arrow shown by the driving means (not shown) at a peripheral speed of 100 mm / sec.

The developing device 4 is provided with a support 9 which rotates around a rotation shaft 9a at its center, and a yellow developing device 4a, a magenta developing device 4b, a cyan developing device 4c and a black developing device 4d are installed on the supporting member 9. It is done. Developing device 4a,
Each of 4b, 4c, and 4d contains a yellow toner, a magenta toner, a cyan toner, and a black toner, which are one-component developers.

In each of the developing devices 4a, 4b, 4c and 4d,
As shown in FIG. 5, the opening surfaces 5a, 5b, 5c, 5d
Developing sleeve 8a as a developer carrying member,
8b, 8c and 8d are installed. Further, each developing device 4
a, 4b, 4c and 4d have coating rollers 6a, 6b,
6c, 6d and toner regulating members 7a, 7b, 7c, 7
d is installed. Developing sleeves 8a, 8b, 8c,
With the rotation of 8d, the coating rollers 6a, 6b, 6c, 6d
The toner is applied onto the developing sleeves 8a, 8b, 8c, 8d by the toner, and the toner applied by the toner regulating members 7a, 7b, 7c, 7d is regulated, and triboelectrified charges are applied to the toner, and the developing sleeves 8a, 8b, 8
A thin toner layer is formed on c and 8d. The toner regulating members 7a to 7d are preferably made of a material that is charged opposite to the charging polarity of the toner, such as nylon when the toner is negatively charged and silicone rubber or the like when the toner is positively charged. good.

The developing sleeves 8a to 8d of the developing devices 4a to 4d, respectively.
The peripheral speed of 8d is 1.0 to the peripheral speed ratio with respect to the photosensitive drum 1.
It is preferable to select it so that the range is 2.0 times.
When the developing devices 4a to 4d face the photosensitive drum 1, the developing devices 4a to 4d are driven so that their opening surfaces 5a to 5d always face the photosensitive drum 1. Details of the driving method of the developing devices 4a to 4d are as described in JP-A-50-93437.

The transfer device 10A is provided with a transfer drum 10 as a transfer material carrier, and around the transfer drum 10, an adsorption roller 23, a discharging charger 2, a separating claw 24, a cleaner 27 and a discharging roller 28 are arranged. There is. Transfer drum 10
As shown in FIG. 6, the gripper 22 of the transfer material gripping member is provided at one location on the outer peripheral surface of the gripper. The transfer drum 10 is rotated in the arrow direction at substantially the same speed as the photosensitive drum 1 by a driving unit (not shown).

The transfer drum 10 is a metal cylinder 10a.
An elastic layer 10b made of foamed rubber or foamed resin is provided on the
An insulating layer 10c serving as a transfer material supporting member is provided thereon. In this example, the metal cylinder 10a has a diameter of 15
The elastic layer 10b was formed to have a thickness of 6 mm, and the elastic layer 10b was formed to have a thickness of 2 mm by winding using urethane foam made of Inoac, and the insulating layer 10c was formed to have a thickness of 100 μm by using a PVdF film.

In the image forming apparatus having the above structure, first, a constant current of 500 μA is applied to the charging device 3 so that the charging device 3 primarily charges the surface of the photosensitive drum 1 to about -700V.
Then, a signal in accordance with the image pattern of the first color, for example, yellow is input to the laser diode 11 to generate light of the image pattern of yellow, and the photosensitive drum 1 is irradiated with the light through the optical path 16 to be exposed. The light irradiator is approximately -10 on
An electrostatic latent image having a yellow image pattern of 0V is formed. The electrostatic latent image of the yellow image pattern formed on the photosensitive drum 1 is developed by the yellow developing device 4a located in the developing unit facing the developing device 4 as the photosensitive drum 11 rotates, and is exposed to light. A yellow toner image is formed on the drum 1.

On the other hand, the transfer paper is supplied from the transfer material cassette 17 to the transfer drum 10 of the transfer device 10A by the pickup roller 18 in synchronization with the image on the photosensitive drum 1. The transfer drum 10 transfers the supplied transfer paper to the gripper 2
The photosensitive drum 1 is gripped and rotated by
The image is transferred to the image transfer section opposite to. The transfer sheet conveyed to the image transfer section receives yellow toner on the photosensitive drum 1 by a transfer voltage applied between the transfer drum 10 and the photosensitive drum 1 via a metal cylinder 10a of the transfer drum 10 by a power source (not shown). The image is transferred.

At the same time as this transfer, charges are injected into the transfer paper by the transfer voltage, and the transfer paper is electrostatically adsorbed and held on the surface of the transfer drum 10. In order to enhance the electrostatic attraction of the transfer paper to the surface of the transfer drum 10, the transfer drum 10
The transfer roller 23 may be installed near the paper feeding unit and the transfer voltage may be applied so that the transfer paper is electrostatically adsorbed in advance after being gripped by the gripper 22.

After the transfer of the yellow toner image is completed, the photosensitive drum 1 is cleaned by a cleaning member such as a fur brush or a blade installed on the cleaner 26 to remove the residual toner on the surface thereof, and then the primary charging by the charger 3 is performed. An image forming operation is performed.

Primary charging of the photosensitive drum 1 as described above, formation of an electrostatic latent image by exposure, formation of a toner image by development of the electrostatic latent image, and superposition transfer of the obtained toner image onto a transfer paper are performed. By performing the process for magenta, cyan, and black for the second and subsequent colors, a color image in which toner images of four colors of yellow, magenta, cyan, and black are superimposed and transferred on the transfer paper can be obtained.

The transfer paper on which the four color toner images have been transferred is then discharged by the discharging charger 2 arranged around the transfer drum 10, and then separated from the transfer drum 10 by the separating claw 24 on the downstream side. And is sent to the fixing device 25. There, the toner images of four colors are fixed by heating and pressurization, the toner images are mixed and fixed on the transfer paper to form a full-color permanent image, which is then discharged outside the image forming apparatus. Preferably, the residual toner on the surface of the transfer drum 10 from which the transfer paper is peeled off is cleaned by a cleaner 27 having a cleaning member such as a fur brush or a web.

[0016]

By the way, it is preferable that the peripheral length of the transfer drum 10 and the peripheral length of the photosensitive drum 1 have an integer ratio relationship. This is because if the peripheral lengths are set to an integer ratio, when toner images of two or more colors are formed, even if the photosensitive drum 1 has unevenness, the same unevenness occurs in the same portion for each color. Even if they are stacked, slight unevenness in shades will suffice. If this does not take an integer ratio, the position of the unevenness shifts for each color, resulting in color unevenness and significantly impairing the image quality.

The transfer drum 10 is in contact with the photosensitive drum 1 with a nip at the time of transfer, but when the transfer drum 10 is stopped during non-transfer, the PVdF film serving as a transfer material supporting member on the surface of the transfer drum 10. The insulating layer 10c is made to be in non-contact with the photosensitive drum 1 in consideration of deformation and the like due to pressure contact.

Therefore, since the gripper 22 shown in FIG. 6 is not in contact with the photosensitive drum 1 when the transfer drum 10 is stopped,
The position where the gripper 22 is opposed to the photosensitive drum 1 is the home position of the transfer drum 10, and the transfer drum 10 is always stopped at this position.

However, as a result of the study by the present inventors, the following problems have occurred.

The peripheral lengths of the photosensitive drum 1 and the transfer drum 10 are always in phase with each other at an integer ratio.
Since the stop position of 0 is always a constant position, the stop position of the photosensitive drum 1 is also a constant position, and the photosensitive drum 1 always faces the primary charger 3 that charges the same.

When a corona charger is used as the primary charger 3, the charger ₃ generates NOx and O ₃ at the time of charging, whereby the nitric acid compound adheres to the shield surface of the charger 3. This nitric acid compound is gradually released from the shield surface and contaminates the opposing photosensitive drum 1. Contamination of the photosensitive drum 1 by the nitric acid compound is not a problem since it is extremely small once, but as described above, since the same position of the photosensitive drum 1 always faces the charger 3, the contamination by the nitric acid compound is caused. Occurs in large amount on the photosensitive drum 1,
Surface is damaged. For this reason, the surface resistance of the photosensitive drum 1 is lowered, and the electrostatic latent image formed on the photosensitive drum 1 is disturbed and blurred, which causes a problem that the image obtained by development is blurred.

In recent years, the generation of O ₃ is extremely small,
A contact charging means has been put into practical use which does not cause the problem itself of the charging wire being contaminated or broken (JP-A-57-17).
8267, 56-104351, 58-40566, 5
8-139156, 58-150975, etc.).

According to the primary charger composed of the contact charging means, the photosensitive drum 1 is hardly damaged by the contamination of nitric acid compound, O ₃ , or NOx, but the charging member such as an elastic body is directly contacted with the photosensitive drum 1. Therefore, the photosensitive drum 1 is contaminated by the plasticizer, oil, etc. contained in the charging member. Contamination due to this is not a problem even once, but as described above, since the photosensitive drum 1 always faces the contact charging unit at the same position, the contamination from the charging member accumulates on the photosensitive drum 1 as a contact mark. , As well, with the result of spoiling the image.

Therefore, in order to avoid these, the drive of the transfer drum 10 is separated from the drive of the photosensitive drum 1, the transfer drum 10 and the photosensitive drum 1 are separated, and only the photosensitive drum 1 is kept with the transfer drum 10 stopped. It is considered that only the stop position of the photosensitive drum 1 is displaced from the previous stop position by rotating a small amount.

According to this, although the effect of preventing the contamination of the photosensitive drum 1 by the plasticizer or the like from the charging member of the contact charging means is sufficient, however, there is a big drawback that the apparatus becomes complicated and the cost increases. As a result, there were many practical problems.

An object of the present invention is to provide an image carrier which has a perimeter ratio substantially equal to that of the transfer medium carrier and which is stopped at the same time when the transfer medium carrier is stopped, installed around the image carrier. By preventing the same place from being contaminated by the contaminants from the primary charging means, it is possible to always perform good primary charging of the image carrier to stably obtain a high-quality image. It is to provide a device.

[0027]

The above object can be achieved by an image forming apparatus according to the present invention. In summary, the present invention is to charge and image-exposure an image bearing member to form an electrostatic latent image, develop the latent image to visualize it as a toner image, and obtain the obtained toner image from the image bearing member. After being transferred onto a transfer material carried on a transfer material carrier having a perimeter substantially equal to the perimeter of, the transfer material having the toner image transferred thereon is peeled from the transfer material carrier, In the image forming apparatus for stopping the rotation of the transfer material carrier and the image carrier, the stop position of the transfer material carrier is different from the previous stop position. Preferably, a region that is not in contact with the image carrier is provided on the outer peripheral surface of the transfer medium carrier, and the stop position of the transfer medium carrier is set at a position where the non-contact region faces the image carrier and the previous time. The stop position is different from the stop position.

[0028]

1 is a sectional view showing a transfer drum and a photosensitive drum in an embodiment of an image forming apparatus of the present invention.
The transfer drum 20 has a diameter of 160 mm and a peripheral length of 502.7 mm, and the photosensitive drum 1 has a diameter of 40 mm and a diameter of 125 mm.
It has a peripheral length of 6 mm, and the peripheral lengths of the transfer drum 20 and the photosensitive drum 1 are in an integral ratio of four.

In the present invention, the elastic layer 20b on the metal cylinder 20a and the elastic layer 20b on the metal cylinder 20a are wound around the outer peripheral surface of the transfer drum 20 from the gripper 22, which is the home position, to the downstream side in the rotational direction of the transfer drum 20. P
A portion (hereinafter referred to as a cutout portion) 20d where the insulating layer 20c made of a VdF film is not provided is provided.
In this embodiment, the arc length H of the cutout portion 20d is set to about 130 mm, which is slightly longer than the circumference of the photosensitive drum 1 (125.6 mm).

Further, on the outer peripheral surface of the transfer drum 20, a home position lever 31 is installed at a position close to the cutout portion 20d on the upstream side with respect to the rotation direction of the transfer drum 20, and the home position of the transfer drum 20 is provided by the lever 31. The home position sensor 32 for detecting that the sheet has passed is installed close to the photosensitive drum 1 outside the transfer drum 20 at a position farther than the length H.

The other mechanical structure of the image forming apparatus of this embodiment is basically the same as that of the conventional image forming apparatus shown in FIG. 4, and therefore its explanation is omitted.

In the image forming apparatus of this embodiment, the normal image forming operation is performed in the same manner as the conventional one.

Next, after the image forming operation is completed and the post-rotation operation of the photosensitive drum 1 and the operation of separating the transfer paper from the transfer drum 20 are completed, in this embodiment, as shown in FIG. The sensor 32 detects the passage of the home position of the transfer drum 20 via the lever 31, and the cutout portion 20d of the transfer drum 20 is connected to the photosensitive drum 3 after an appropriate time t (seconds) has elapsed from the time of the passage detection. The transfer drum 20 and the photosensitive drum 1 are stopped at the same time when they enter the opposing non-contact position, and the time from the passage detection to the stop, that is, the above-mentioned t (second) is stored.

When the transfer drum 20 and the photosensitive drum 1 are stopped after the next image forming operation, the transfer drum 20 is positioned at the non-contact position with the photosensitive drum 3 after detecting the passage of the home position. The time (t + α) obtained by adding an appropriate small time α (seconds) to the above time t
After (seconds), the transfer drum 20 and the photosensitive drum 1 are stopped at the same time, and the time (t + α) is stored.

This small time α is the process speed v
_p, when the primary charger 3 of the opening width formed of a corona charger is is h, it is preferable that α> h / v _p. By doing so, the portion of the photosensitive drum 1 facing the charger 3 at the previous stop is stopped at the position completely deviated from the charger 3 to the downstream side at the next stop.

The time until such a stop is time α
The image formation is performed while repeating the operation of stopping the transfer drum 20 and the photosensitive drum 1 while gradually increasing the shift position to shift the stop position, and the time until the stop when the gripper 2 reaches the position of the photosensitive drum 1 is stored ( Stop operation n
The time until the stop is (t + (n-1) α)
Then, after returning to the beginning and detecting the passage of the home position, the transfer drum 20 is stopped at the time t to start again.

According to this, since the surfaces of the transfer drum 20 and the photosensitive drum 1 are not in contact with each other, and the stop position always deviates from the stop position of the previous rotation, the photosensitive drum 1 is charged. The position facing 3 will not always be the same. Therefore, it is possible to prevent a large amount of the same portion of the photosensitive drum 1 from being contaminated by the contaminants from the primary charger 3. Further, the photosensitive drum 1 does not receive the charging memory of the transfer drum 20.

Further, for example, the transfer drum 20 after repeating the operation.
Stop at the same position as before and the photosensitive drum 1 also comes to the same position as before, the cutout portion 20d of the transfer drum 20 is sufficiently longer than one revolution of the photosensitive drum 1, By the time the drum 20 returns to the original position, the photosensitive drum 1 is subjected to image formation for a long time in total, and during the image forming operation during that time, the contamination of the photosensitive drum 1 is removed by the cleaning blade or the like, and the image formation is sufficiently performed. Be refreshed.

From the above, according to the present invention, the photosensitive drum 1
It is possible to prevent the damage due to the contamination from the primary charger 3 and to always positively charge the photosensitive drum 1 satisfactorily, and it is possible to stably obtain a high-quality image without deteriorating the image quality due to poor charging. Further, in order to prevent the contamination of the photosensitive drum 1, a large operation such as separating the photosensitive drum 1 from the transfer drum 20 and shifting the phase thereof is not performed, so that the cost of preventing the contamination of the photosensitive drum 1 increases. In addition, the reliability of the image forming apparatus does not deteriorate.

FIG. 3 is a sectional view showing a transfer drum and a photosensitive drum in another embodiment of the image forming apparatus of the present invention. In this embodiment, the charging roller 30 of the contact charging means is used as the charging means of the photosensitive drum 1. The outer diameter of the photosensitive drum 1 is 35 mm, and the outer diameter of the transfer drum 20 is 140 mm, which is four times that of the photosensitive drum 1. The cutout portion 20d of the transfer drum 20, which is not provided with the elastic layer 20b and the insulating layer 20c formed by winding the PVdF film, has a length of 70 m.
It is as m.

In the above construction, the operation is the same as in the previous embodiment, but the time α'which increases with each stop is set.
Is α '> L / v _p , where L is the nip between the charging roller 30 and the photosensitive drum 1. The nip L is much smaller than the opening width h of the charger 3 of the previous embodiment (L = 1 to 2 m).
Therefore, α ′ is much smaller than α.

Therefore, in this embodiment, the length of the contact portion of the transfer drum 20 with the photosensitive drum 1, that is, the cutout portion 20d is shorter than the peripheral length of the photosensitive drum 1 and does not correspond to one round of the photosensitive drum 1. Although the length is set, the number of times of shifting the stop positions of the transfer drum 20 and the photosensitive drum 1 is very large. Therefore, the effect of preventing contamination of the photosensitive drum 1 is obtained in the first embodiment.
Although it is equivalent to the above, the area where the transfer paper is wound around the transfer drum 20 can be effectively used, and as a result, the diameter of the transfer drum 20 can be reduced and the apparatus can be downsized.

Still another embodiment of the present invention will be described. In this embodiment, the mechanical structure of the transfer drum is the same as that of the embodiment shown in FIG. In this embodiment, the power is turned on to rotate the transfer drum 20, and the time from the start of rotation until the passage of the home position of the transfer drum 20 is detected is detected. The stop position of 20 is detected, and the next stop position is set based on this position.

In all of the above embodiments, the next stop position is determined by storing the previous stop position by the time until the stop after passing the home position. Therefore, when the power is turned off. Since it was reset, the control of the stop position had to be started from the beginning at the next ON, and in order to avoid this, it was necessary to provide a backup memory. According to the present embodiment, this detects the stop position when the power is turned off and uses this as the reference for the next stop position setting. Therefore, even if there is no backup memory, control of the stop position does not return to the beginning, You can start from.

In each of the above embodiments, the transfer drum is provided with the gripper and the transfer drum is provided with the non-contact area with the photosensitive drum. However, the present invention is not limited to this, and the transfer material supporting member on the surface is used. With a seamless transfer drum in which a certain insulating layer is provided seamlessly in the circumferential direction, even if the transfer drum is always in contact with the photosensitive drum, by changing the stop position of the transfer drum each time with respect to the home position, The same effect can be obtained.

[0046]

As described above, in the image forming apparatus of the present invention, the transfer material carrier is provided with an area that is not in contact with the image carrier, and the non-contact area is an image when the transfer material carrier is stopped. Since the image carrier is stopped by positioning it so as to face the carrier, and the stop position is different from the previous stop position in the non-contact area, the image carrier that is stopped at the same time as the transfer material carrier is stopped. Even if it has a relationship of an integral multiple perimeter ratio with the transfer material carrier, the portion facing the corona charger, which is the charging means of the image carrier, or the portion in contact with the charging member of the contact charger is displaced each time, For this reason, the same portion of the image bearing member is not contaminated in large amounts by the pollutant from the charging means, and the same portion is contaminated by returning to the position where the image bearing member has already stopped once. Even so, the frequency is low and The surface of the image bearing member by the cleaning blade or the like during the image forming operation of the return is sufficiently refreshed. Therefore, in any case, the image carrier can always be favorably primary-charged, and deterioration of the image quality due to poor charging can be eliminated, and a high-quality image can be stably obtained.

[Brief description of drawings]

FIG. 1 is a sectional view showing a transfer drum and a photosensitive drum in an embodiment of an image forming apparatus of the present invention.

FIG. 2 is a cross-sectional view showing a control method of stop positions of the transfer drum and the photosensitive drum of FIG.

FIG. 3 is a sectional view showing a transfer drum and a photosensitive drum in another embodiment of the image forming apparatus of the invention.

FIG. 4 is a cross-sectional view showing the overall configuration of a conventional image forming apparatus.

5 is a sectional view showing a rotary developing device installed in the image forming apparatus of FIG.

6 is a perspective view showing a part of a transfer drum of a transfer device installed in the image forming apparatus of FIG.

[Explanation of symbols]

 1 Photosensitive Drum 3 Primary Charger 20 Transfer Drum 20A Transfer Device 20a Metal Cylinder 20b Elastic Layer 20c Insulating Layer 20d Cutout 22 Gripper 30 Charging Roller 32 Sensor

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Tetsuya Kobayashi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Mashiro Saito 3-30-2 Shimomaruko, Ota-ku, Tokyo Kya (72) Inventor Naoki Enomoto 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Tatsuya Kobayashi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Haruo Fujii 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (2)

[Claims] 1. An electrostatic latent image is formed by performing charging and image exposure on an image carrier, developing the latent image to visualize it as a toner image, and the obtained toner image is surrounded by the periphery of the image carrier. The transfer material is transferred onto a transfer material carried on a transfer material carrier having a perimeter that is substantially an integral multiple of the length, and the transfer material on which the toner image is transferred is peeled from the transfer material carrier and then transferred. An image forming apparatus for stopping the rotation of a material carrier and the image carrier, wherein the stop position of the transfer material carrier is different from the previous stop position. 2. An electrostatic latent image is formed by performing charging and image exposure on the image carrier, developing the latent image to visualize it as a toner image, and the obtained toner image is surrounded by the periphery of the image carrier. The transfer material is transferred onto a transfer material carried on a transfer material carrier having a perimeter that is substantially an integral multiple of the length, and the transfer material on which the toner image is transferred is peeled from the transfer material carrier and then transferred. In an image forming apparatus that stops the rotation of the material carrier and the image carrier, a region that is not in contact with the image carrier is provided on the outer peripheral surface of the transfer material carrier, and the stop position of the transfer material carrier is set. An image forming apparatus characterized in that the non-contact region is located at a position facing the image carrier and different from a previous stop position.