Rotation member support configuration and fixing device using same

A rotation member support configuration supports a roller and applies pressure in a direction orthogonal to the rotational axis line of the roller, using a spring attached around a bearing. The spring includes two coils differing from each other in twisting direction and connected at an angle formed with respect to a coil axis line direction.

BACKGROUND

Field of the Disclosure

The present disclosure relates to a rotation member support configuration to be used in an apparatus such as a printer that forms an image on a recording medium, and the rotation member support configuration adds an urging force in a direction orthogonal to the rotational axis line of a rotation member, while supporting the rotation member to be rotatable.

Description of the Related Art

In an image forming apparatus such as a printer and copier, various rotation members including a sheet conveyance roller, a fixing roller, and a cleaning roller are each rotatably supported by an urging force added in a direction orthogonal to the rotational axis line of the rotation member. Japanese Patent Application Laid-Open No. 2015-178402 discusses a rotation member support configuration in which the rotation shaft of one of a pair of rollers for nipping and supporting a sheet is rotatably supported by a bearing, and the other roller of the pair is biased by a pulling spring arranged around the outer periphery of the bearing. A nip pressure is thereby exerted on a contact portion of the pair of rollers, so that a sheet can be conveyed. Such a rotation member support configuration is space-saving and low-cost, so that the configuration is adopted in many products.

In a pressure configuration having a pulling spring around the outer periphery of a bearing, there is used a configuration in which a hook having a shape protruding outward from the outer periphery of a coil of the pulling spring is formed at each of both ends of the coil. In this configuration, a spring hook portion is formed at an end surface of a sheet metal frame that supports the bearing, and the hook of the spring can be hooked onto the spring hook portion, thereby allowing for implementation with low cost and reduced space.

The coil is brought into contact with the outer periphery of the bearing and thereby deformed in a curved shape, and the curved coil of the spring attached around the bearing has a force for returning to a straight line, so that a force in a twisting direction is exerted at a root portion of the hook, which may lower the durability of the spring.

SUMMARY

The present disclosure is directed to a rotation member support configuration for improving durability of an urging member that urges a rotation member in a direction orthogonal to a rotational axis line of the rotation member while rotatably supporting the rotation member, and is also directed to a fixing device using the rotation member support configuration.

According to an aspect of the present disclosure, a rotation member support configuration rotatably supports a rotation member, and the rotation member support configuration includes a rotation member configured to rotate, a bearing portion configured to rotatably support the rotation member, a pressed member configured to be pressed by the rotation member, a spring member configured to press the rotation member toward the pressed member and including hook portions on both ends thereof, a first coil portion formed by spirally winding an element wire, a second coil portion formed by spirally winding an element wire, and a connection portion formed of a linear element wire and connecting the first coil portion and the second coil portion, and a support member configured to support the bearing portion and the pressed member. The spring member is attached by hooking each of the hook portions, provided on the both ends on the support member, such that the connection portion presses the bearing portion.

DESCRIPTION OF THE EMBODIMENTS

An image forming apparatus according to an exemplary embodiment of the present disclosure will be described below in detail with reference to the drawings. In the present exemplary embodiment, a roller support configuration of a cleaning unit included in a fixing device of an electrophotographic printer will be described as an example, but application targets of the present disclosure is not limited thereto.

FIG. 1is a configuration schematic diagram illustrating an image forming apparatus according to the present exemplary embodiment.

In the image forming apparatus illustrated inFIG. 1, first, second, third, and fourth image forming units, i.e., image forming units Pa, Pb, Pc, and Pd, are disposed side by side. The image forming units Pa, Pb, Pc, and Pd form toner images of the respectively different colors through a latent-image forming process, a development process, and a transfer process, and each of the image forming units operates as follows based on an instruction from a central processing unit (CPU) to start image formation.

The image forming units Pa, Pb, Pc, and Pd include respective dedicated image carriers, i.e., in this example, electrophotographic photosensitive drums3a,3b,3c, and3d. The toner images of the respective colors are formed on the respective photosensitive drums3a,3b,3c, and3d. An intermediate transfer member20is disposed next to the photosensitive drums3a,3b,3c, and3d, and the toner images of the respective colors formed on the photosensitive drums3a,3b,3c, and3dare primarily transferred onto the intermediate transfer member20, and then transferred onto a recording medium P at a secondary transfer portion. The recording medium P onto which the toner images have been transferred is conveyed to a fixing device9that fixes the toner images by applying heat and pressure. Subsequently, the recording medium P is discharged to the outside of the image forming apparatus as a recorded image.

FIG. 2illustrates a front sectional view of the fixing device9in the present exemplary embodiment, andFIG. 3illustrates a side view of the fixing device9in the present exemplary embodiment.

The fixing device9includes a fixing roller91as a fixing member, and a pressure roller92as a pressure member. Inside the fixing roller91, a heater (not illustrated) is disposed as a heating unit and configured to heat the fixing roller91to a predetermined temperature. At a fixing nip formed by the fixing roller91and the pressure roller92, the recording medium P carrying an unfixed toner image is nipped and conveyed, and the toner image is fixed to the recording medium P by application of heat and pressure.

A cleaning unit94for removing offset toner adhering to the fixing roller91is disposed near the fixing roller91. The cleaning unit94is attached to be movable between a cleaning position where the cleaning unit94abuts the fixing roller91and a standby position where the cleaning unit94is separated from the fixing roller91.

FIG. 4illustrates the cleaning unit94, and the fixing roller91to be cleaned. For descriptive purposes, a part of a frame943of the cleaning unit94is not illustrated. In the cleaning unit94, a cleaning roller941is rotatably supported, and a cleaning web942is wrapped around the cleaning roller941. A beating944is disposed at each end of the frame943in an image width direction, and supports the cleaning roller941to be rotatable. A pulling spring945is placed around the outer periphery of the bearing944, and urges the cleaning roller941in a direction toward the fixing roller91. When the cleaning unit94is at the cleaning position, the cleaning roller941abuts the fixing roller91, so that the pulling spring945disposed around the outer periphery of the bearing944extends to urge the cleaning roller941toward the fixing roller91. Then, a nipping force to he used for cleaning of the offset toner is generated.

The width of each of the cleaning roller941and the cleaning web942is set to be larger than a maximum width of an image that can be formed by the image forming apparatus. The offset toner adhering to the surface of the fixing roller91is collected by the cleaning web942at a cleaning nip portion formed by the fixing roller91and the cleaning roller941when the fixing roller91rotates.

<Support for Cleaning Roller and Pressure Configuration>

A rotation member support configuration will be described in detail.

The frame943(a support member) of the cleaning unit94that is an example of the rotation member support configuration has such a configuration that a side plate of a sheet metal is disposed at each end thereof in the image width direction.

FIG. 5illustrates details of a bearing portion that supports the cleaning roller941that is a rotation member that rotates.FIG. 6andFIG. 7are diagrams that illustrate the bearing944, and.FIG. 8is a diagram that illustrates the pulling spring945(a spring member) disposed around the outer periphery of the bearing944. The cleaning roller941is configured to press the fixing roller91, i.e., a pressed member, via the cleaning web942.

The bearing944(the bearing portion) that supports the cleaning roller941rotating can be slidably supported by a guide portion9431located at the side plate. Formed at each of both ends of the pulling spring945placed around the outer periphery of the bearing944is a hook9454(a hook portion) having a shape protruding from the outer periphery of each of a first coil9451(a coil portion) and a second coil9452(a coil portion) of the pulling spring945. The hook9454is secured to a spring hook portion9432formed on an end surface of the side plate.

The bearing944includes a hole9441for supporting rotation of the cleaning roller941, and a guide portion9442to be engaged with the guide portion9431of the side plate of the cleaning unit94. A spring support portion9443has a shape protruding in a direction opposite to the pressing direction of the cleaning roller941from a concentric circle B of the inner diameter of the hole9441and passing through each point A where the pulling spring945abuts the bearing944at a position closest to the hole9441. In other words, the spring support portion9443is a convex-shaped portion. The pulling spring945is placed around the spring support portion9443. A spring coil contact surface9444of the spring support portion9443is formed with a curvature radius larger than that of the above-described concentric circle B. Disposed at a position the bearing944is to be engaged with a connection portion9453of the pulling spring945is a rib9445(a wall portion) that prevents the connection portion9453from falling off the end portion of the cleaning roller941.

The pulling spring945has a configuration in which the connection portion9453connects the first coil9451(the coil portion) and the second coil9452(the coil portion) that vary in winding direction. Disposed at an end portion of each coil portion opposite to the connection portion9453is the hook9454that protrudes outward from the outer periphery of the coil facing the hook9454. The shapes of these are formed from a single rod in a continuous manner. In the present exemplary embodiment, the material of the pulling spring945is stainless steel. The thickness of the wire is 0.8 mm. The outside diameter of each of the first coil9451and the second coil9452is 4 mm. The free length of each of the first coil9451and the second coil9452is 10 mm, and the length of the connection portion9453is 6 mm. The life of a coil tends to be short if the free length of the coil is short. Therefore, in the present exemplary embodiment, the length of the connection portion9453is as short as possible to increase the free length of each of the first coil9451and the second coil9452. For this reason, the free length of each of the first coil9451and the second coil9452is longer than the length of the connection portion9453. The above-described size of the pulling spring945is a mere example and the size thereof is not limited thereto.

The connection portion9453has a shape that is bent and raised in a direction of a coil axial line from the winding end of each of the first coil9451and the second coil9452. Because the connection portion9453is provided with such a bent portion, an angle is formed in the direction of the axis line of each of the first coil9451and the second coil9452. As illustrated inFIG. 5, the pulling spring945is attached so that the connection portion9453is supported at the top of the spring support portion9443of the bearing944. If an angle formed by the directions of the axis lines of the first coil9451and the second coil9452is made small and the protrusion amount of the spring support portion9443of the bearing944is made large, the coil length when the pulling spring945is placed around the bearing944can be made long, which allows for a spring design with a small spring constant. In a case where the pulling springs945are designed to have an equal spring force for urging the cleaning roller941, the variation in spring force due to the variation in component dimension can be reduced by a smaller spring constant. In addition, the amplitude of a stress variation that occurs in the pulling spring945due to attachment/detachment operation of the cleaning unit94can be made small, and thus the durability of the pulling spring945can be increased.

Although the angle formed by the axial lines (free length directions) of the first coil9451and the second coil9452varies depending on a space available for implementation of the pulling spring945and a desirable swing force, this angle is desirably 120 degrees or less so that the sum of the lengths of these two coils is longer than the coil length of a conventional swing.

Meanwhile, if the angle formed by the axial lines of the first coil9451and the second coil9452is acute, the following issue arises. When the pulling spring945is manufactured using a forming machine, the first-formed coil interferes with the machine when the second coil is formed. To avoid this issue, the angle formed by the axial lines of the first coil9451and the second coil9452is desirably 80 degrees or more. If this angle is smaller than 80 degrees, it may be necessary to perform a process for bending the connection portion9453besides the process using the forming machine. This leads to an increase in cost.

In other words, the angle formed by the axial lines of the first coil9451and the second coil9452is desirably 80 degrees or more and 120 degrees or less. In the present exemplary embodiment, the angle formed by the axial lines of the first coil9451and the second coil9452is 90 degrees.

The hook9454at the end portion of each of the first coil9451and the second coil9452needs to protrude toward the side plate when the pulling spring945is placed around the bearing944. In consideration of workability for securing the hook9454to the spring hook portion9432of the side plate, an angle formed by the hook9454at one of the end portions of the first coil9451and the second coil9452and the other coil when viewed from the direction of the axis line of the other coil is desirably 90±45 degrees, i.e., in a range of 45 degrees or more and 135 degrees or less. In the present exemplary embodiment, when viewed from the direction of the axis line of the first coil9451, the angle formed by the hook9454of the first coil9451and the second coil9452is 90 degrees, as illustrated inFIG. 9.

FIG. 10illustrates a state where the pulling spring945is placed around the bearing944. The first coil9451and the second coil9452of the pulling spring945are connected by the connection portion9453at an angle of 90 degrees therebetween, and the hooks9454at the other ends opposite of the connection portion side are attached so that the directions of the coil axis lines are parallel to a pressing direction C of the cleaning roller941. For this reason, a curvature is formed in each of the coils, and a force D for returning the coil to a straight line is generated. The coil tends to return to the straight line in a state where the hook9454protruding outward from the outer periphery of the coil is secured to the spring hook portion9432of the side plate, and thus a twisting force E occurs at a root portion of the hook9454at each end of the pulling spring945.

Here, a force that acts on a spring in a conventional rotation member support configuration will be described with reference toFIG. 11, for comparison.

In a conventional spring947, a hook9472is formed at each end of one coil9471, and the hook9472has a shape protruding outward from the outer periphery of the coil9471.FIG. 11illustrates a state where the conventional spring947is placed around the outer periphery of a cylindrical bearing. The coil9471curved at 180 degrees is placed around the bearing, and a force D for returning the coil9471to a straight line occurs at each of the coil9471. The coil9471tends to return to the straight line in a state where the hook9472protruding outward from the outer periphery of the coil9471is secured to a spring hook portion of a side plate, and thus twisting forces E1and E2occur at root portions of the hooks9472located at both ends of the conventional spring947. The directions of these twisting forces at the both ends of the conventional spring947differ from each other. The twisting force E1acts in a direction for loosening the winding of the coil9471, and the twisting force E2acts in a direction for tightening the winding of the coil9471.

When the twisting force acting in a coil circumferential direction is applied to the root of the hook9472in addition to a pulling force of the conventional spring947that is a pulling spring, a greater stress occurs near the root of the hook9472than in a case where only the pulling force acts. In particular, a greater stress occurs in the hook9472on the twisting force E2acts in the direction for tightening the winding of the coil9471than in the hook9472on which the twisting force E1acts in the direction for loosening the winding of the coil9471. The durability of the spring947is affected by the durability of the root portion of the hook9472on which the twisting force E2acts in the direction for tightening the winding of the coil9471, so that the durability of the spring947can be reduced.

The force that acts on the pulling spring945of the present exemplary embodiment will be confirmed with reference toFIG. 10, again.

In the pulling spring945according to the present exemplary embodiment, the first coil9451and the second coil9452are each curved at 45 degrees, i.e., the curvature of 90 degrees in total is formed. Therefore, the force D for returning the pulling spring945to the straight line and the twisting force E that occurs at the root portion of the hook9454are smaller than those of the conventional spring947. Further, in the pulling spring945according to the present exemplary embodiment, the winding directions of the first coil9451and the second coil9452are opposite from each other. Specifically, the first coil9451is wound clockwise, and the second coil9452is wound counterclockwise. In both of these coils, the twisting force E that occurs at the hook root portion acts in the direction for loosening the winding of the coil. A stress that occurs at the hook root portion due to the twisting force in this direction is small, as compared with that in the direction for tightening the winding of the coil.

As described above, the rotation member support configuration according to the present exemplary embodiment can improve the spring durability for the following reasons, compared to the conventional rotation member support configuration.The spring has the configuration in which the two coils are connected, so that the spring constant is reduced, and the amplitude of the stress that occurs in the spring is made small.The curvature of the coil of the spring placed round the bearing is made small, so that the twisting force exerted near the hook is reduced.The two coils wound in different winding directions are used, and the twisting force exerted near the hook acts in the direction for loosening the coil, so that the stress that occurs due to the twisting force is reduced.

In the above-described exemplary embodiment, description is given using a configuration in which the cleaning roller that is the rotation member presses the fixing roller that is the pressed member. The present disclosure is not limited to this exemplary embodiment. For example, the present disclosure is also applicable to, other than the cleaning roller, a metal roller that presses the pressure roller of the fixing device. The present disclosure is also applicable to, other than the fixing device, a conveyance roller that presses another roller.

This application claims the benefit of priority from Japanese Patent Application No. 2019-111593, filed Jun. 14, 2019, which is hereby incorporated by reference herein in its entirety.