Fixing device, image formation device, control method and control program

Abstract

To improve print quality.SOLUTION: A fixing device 100 applies pressure to a sheet S on which a toner image is adhered to fix the toner image. The fixing device 100 includes: a pressure roller 81; a drive roller 82 which forms a fixing nip N facing the pressure roller 81 and has a higher surface hardness than the pressure roller 81; an entrance guide 85 which is configured to rotate around a rotation axis Ax parallel to the drive roller 82 and guides the sheet S entering the fixing nip N; and a control part 17 which controls the rotational position of the entrance guide 85 around the rotation axis Ax in accordance with sheet rigidity information regarding the hardness of the sheet S.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a fixing device for fixing a toner image on a sheet of paper, an image forming apparatus, a control method, and a control program. [Background technology]

[0002] In the image forming apparatus, the paper onto which the unfixed toner has been transferred is heated and pressed in a fixing nip to fix the toner image onto the paper. In Patent Document 1, an entry guide that guides paper into the fixing nip is moved in conjunction with the deformation of the fixing nip to a position that corresponds to the deformed fixing nip, thereby properly guiding paper into the deformed fixing nip. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-181760 Summary of the Invention [Problem to be solved by the invention]

[0004] However, with the above-described conventional technology, the paper is subjected to an impact when the leading edge of the paper hits the hard fixing roller, which can cause image unevenness in the direction perpendicular to the conveyance direction at the transfer section upstream of the fixing section. This impact can be reduced by guiding the paper so that the leading edge of the paper enters a position close to the fixing nip. However, in this case, if the paper does not enter the fixing nip smoothly, the paper may wrinkle.

[0005] The present invention has been made in view of the above circumstances, and has as its object to improve print quality. [Means for solving the problem]

[0006] In order to achieve the above object, the present invention provides a fixing device that applies pressure to a sheet of paper on which a toner image is attached to fix the toner image, the fixing device comprising: The first roller, a second roller that faces the first roller to form a fixing nip and has a surface that is harder than the first roller; an entrance guide configured to be rotatable about a rotation axis parallel to the second roller and to guide the paper entering the fixing nip; a control unit that controls a rotation position of the inlet guide around the rotation axis based on paper stiffness information relating to the hardness of the paper; Equipped with. [Effects of the Invention]

[0007] According to the present invention, print quality can be improved. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment. [Figure 2] FIG. 2 is a block diagram showing a schematic control configuration of the image forming apparatus according to the embodiment. [Figure 3] FIG. 2 is a diagram illustrating a fixing unit according to the embodiment. [Figure 4] FIG. 2 is a perspective view showing an inlet guide and a support member according to the embodiment. [Figure 5] FIG. 2 is a perspective view showing a support member, a cam member, and a motor according to the embodiment. [Figure 6A] FIG. 10 shows the inlet guide and the support member in a first rotational position. [Figure 6B] FIG. 10 shows the inlet guide and the support member in a second rotational position. [Figure 7] FIG. 10 is a diagram for explaining a modified example of the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0010] [Overall configuration of image forming device] FIG. 1 is a diagram showing the overall configuration of an image forming apparatus 1 according to this embodiment. As shown in this diagram, the image forming apparatus 1 according to this embodiment forms an image using an electrophotographic process, reading an image from an original and forming (transferring, printing) it on paper S. The image forming apparatus 1 also receives job data including image data and setting information in PDL (Page Description Language) format from an external client terminal via a network. The image forming apparatus 1 then forms an image on paper S based on this job data. The client terminal is, for example, a PC, a tablet terminal, a smartphone, etc. Specifically, the image forming apparatus 1 includes an image reading unit 2, an image forming unit 3, an intermediate transfer unit 4, a paper feeding unit 5, a paper conveying unit 6, a secondary transfer unit 7, and a fixing unit 8.

[0011] The image reading unit 2 reads an original document using the scanning exposure means 21 and outputs an image information signal (image data). That is, an image of an original document placed on an original table 22 is scanned and exposed by an optical system that constitutes the scanning exposure means 21, and is read into a line image sensor.

[0012] The image forming unit 3 includes five image creating units 31 that form toner images of the respective colors of yellow (Y), magenta (M), cyan (C), black (K), and special color (Z) (for example, white (W)). Each image forming unit 31 forms a toner image of each color on a photoreceptor 32 and performs primary transfer of the toner image onto an intermediate transfer belt 41. Each image forming unit 31 includes a photoreceptor 32, a charging device 33, an exposure device 34, a developing device 35, and a cleaning unit 36.

[0013] The photoreceptor 32 is a drum-shaped image carrier that carries an image (toner image) on its surface. The photoreceptor 32 is an organic photoreceptor in which a photosensitive layer made of a resin containing an organic photoconductor is formed on the outer peripheral surface of a drum-shaped metal substrate, and is driven to rotate counterclockwise in the drawing.

[0014] The charging device 33 uniformly charges the surface of the photoreceptor 32 to a constant potential. The exposure device 34 exposes the non-image area of ​​the photoreceptor 32 to light based on the image data from the image reading unit 2, and forms an electrostatic latent image in the image area of ​​the photoreceptor 32. Note that the image data is not limited to data output from the image reading unit 2, and may be data received from an external device such as a client terminal. The developing device 35 supplies toner, which is a developer, onto the electrostatic latent image formed on the photoreceptor 32 , thereby forming a toner image on the photoreceptor 32 . The cleaning unit 36 ​​removes the toner remaining on the surface of the photoreceptor 32 using, for example, a blade method.

[0015] The intermediate transfer unit 4 includes an intermediate transfer belt 41 and a primary transfer roller 42 . The intermediate transfer belt 41 is a belt-shaped image carrier that is stretched over a plurality of rollers, carries an image (toner image) on its surface, and conveys the image in the moving direction T. The primary transfer rollers 42 are disposed opposite each photoconductor 32 with the intermediate transfer belt 41 sandwiched therebetween. The primary transfer rollers 42 press the intermediate transfer belt 41 against each opposing photoconductor 32, and perform primary transfer of the toner image formed on the photoconductor 32 onto the intermediate transfer belt 41.

[0016] The paper feed unit 5 includes a plurality of trays 51 that store paper S as recording media. The plurality of trays 51 store paper S of different sizes, paper qualities, paper types, etc. The paper S is sent from the paper feed unit 5 onto a transport path of the paper transport unit 6.

[0017] The paper transport unit 6 has a plurality of rollers 61 and transports the paper S sent out from the paper feed unit 5. The paper S supplied from the tray 51 of the paper feed unit 5 passes through registration rollers 62 and is transported to the secondary transfer unit 7. Furthermore, the paper transport section 6 includes a paper inverting section 63. The paper inverting section 63 inverts the paper S on which the image has been fixed by the fixing section 8 from front to back.

[0018] The secondary transfer unit 7 has a pair of secondary transfer rollers 71. The pair of secondary transfer rollers 71 are in pressure contact with each other via the intermediate transfer belt 41, forming a secondary transfer nip therebetween. The secondary transfer nip brings the paper S conveyed by the paper conveying unit 6 into contact with the intermediate transfer belt 41, and performs a second transfer of the toner image carried on the surface of the intermediate transfer belt 41 onto the paper S.

[0019] The fixing unit 8 is disposed downstream (discharge side) in the conveying direction of the paper S from the secondary transfer unit 7. The fixing unit 8 heats and pressurizes the conveyed paper S, and fixes the toner image transferred to the paper S. The configuration of the fixing unit 8 will be described in detail later.

[0020] FIG. 2 is a block diagram showing a schematic control configuration of the image forming apparatus 1. As shown in FIG. 2, in addition to the above-mentioned units, the image forming apparatus 1 includes an operation unit 11, a display unit 12, a communication unit 14, a storage unit 16, and a control unit 17. The fixing device 100 according to the present invention is configured to include the fixing unit 8 and the control unit 17.

[0021] The operation unit 11 is an operation means by which an operator performs various operations to operate the image forming apparatus 1, and includes input devices such as a mouse and a keyboard. The display unit 12 is, for example, a liquid crystal display, an organic electroluminescence display, or another display. The display unit 12 displays various information based on a display signal from the control unit 17. The display unit 12 may also be a touch screen that also serves as at least a part of the operation unit 11. The communication unit 14 is connected to a client terminal such as a PC via a network, and transmits and receives various data such as image data and job data.

[0022] The storage unit 16 is a memory configured, for example, by RAM (Random Access Memory), ROM (Read Only Memory), etc. The storage unit 16 stores various programs and data, including a program for executing rotation control of the inlet guide 85, which will be described later, and also functions as a work area for the control unit 17. The control unit 17 is configured with, for example, a CPU (Central Processing Unit) and controls the operation of each unit of the image forming apparatus 1. Specifically, the control unit 17 loads a program stored in advance in the storage unit 16 based on the operation content of the operation unit 11, and executes various processes in cooperation with the loaded program.

[0023] [Overall configuration of the fixing unit] FIG. 3 is a diagram showing the fixing unit 8. As shown in FIG. 3, the fixing unit 8 includes a pressure roller (first roller) 81, a drive roller (second roller) 82, a fixing belt 83, and a heating roller 84. The pressure roller 81, the drive roller 82, and the heating roller 84 are each arranged along the depth direction Y of the image forming apparatus 1 (the direction perpendicular to the plane of the paper in FIG. 3).

[0024] The pressure roller 81 and the drive roller 82 are in pressure contact with each other via the fixing belt 83, forming a fixing nip N therebetween. The pressure roller 81 is disposed above the drive roller 82. The drive roller 82 has a surface hardness greater than that of the pressure roller 81. Specifically, the drive roller 82 hardly deforms in response to the pressing force from the pressure roller 81. On the other hand, the pressure roller 81 has an elastic layer made of, for example, silicone rubber on the outer periphery of its base. Therefore, at the fixing nip N, the elastic layer of the pressure roller 81 is in contact with the drive roller 82 and is deformed by being pressed by the drive roller 82. The pressure roller 81 may be in the form of a pad instead of a roller.

[0025] The fixing belt 83 is an endless belt that is stretched over multiple rollers including a pressure roller 81 and a heating roller 84. The fixing belt 83 is sandwiched between the pressure roller 81 and a driving roller 82, and forms a fixing nip N with the driving roller 82. The fixing belt 83 is rotated by the driving roller 82 that is driven to rotate while being sandwiched between the pressure roller 81 and the driving roller 82.

[0026] The heating roller 84 is, for example, a metal pipe. Inside the heating roller 84, a heating section 84h is fixed. The heating section 84h is a heat generating element such as a halogen heater, and heats the fixing belt 83 that is stretched around the heating roller 84. A thermistor 84t (see FIG. 2) is provided on the heating roller 84. The thermistor 84t detects the temperature of the heating roller 84 (or the fixing belt 83) and outputs the temperature to the control unit 17. The heating roller 84 may be configured to be rotationally driven. By rotating the heating roller 84, the tension of the fixing belt 83 from the fixing nip N to the heating roller 84 increases. This increases the curvature of the exit of the fixing nip N in the rotation direction of the fixing belt 83, improving the separation performance of the paper S.

[0027] At the fixing section 8, the paper S onto which the toner image has been transferred at the secondary transfer section 7 is transported on the transport path R along the transport direction D with the transferred surface (surface to be fixed) facing the pressure roller 81, and passes through the fixing nip N. At this time, the heat of the fixing belt 83 heated by the heating roller 84 is transferred to the sheet S, whereby the toner image on the sheet S is thermally fixed. In this way, the sheet S passing through the fixing nip N is pressed by the pressure roller 81 and the drive roller 82 and heated by the heat of the fixing belt 83, so that the toner image is fixed onto the sheet S. The sheet S on which the image has been fixed by the fixing unit 8 is discharged to the outside of the image forming apparatus 1 from the sheet discharge unit 65 (see FIG. 1).

[0028] [Fixing section entrance guide] In the fixing unit 8, an entrance guide 85 that guides the sheet S entering the fixing nip N is arranged. The entrance guide 85 is disposed obliquely below and upstream of the fixing nip N in the conveying direction D. The entrance guide 85 is formed in a substantially flat plate shape, and has a planar guide surface 85a on its upper side that is aligned with the depth direction Y and the conveying direction D. The inlet guide 85 is supported rotatably about a rotation axis Ax (see FIG. 6A) parallel to the depth direction Y. The inlet guide 85 is biased around the rotation axis Ax in a rotation direction (counterclockwise in FIG. 3) such that the end portion on the downstream side in the conveying direction D becomes lower.

[0029] Specifically, as shown in FIGS. 4 and 5, the entrance guide 85 is supported by a support member 86 arranged on the rear side (lower side) of the guide surface 85a. The support member 86 has a shaft portion 86a parallel to the depth direction Y, and support portions 86b and follower portions 86c at both ends of the shaft portion 86a. The support portion 86b is provided at one end of the shaft portion 86a, and abuts against the center portion in the depth direction Y of the entrance guide 85 on the rear side of the guide surface 85a. The follower portion 86c is provided at the other end of the shaft portion 86a and is connected to the motor 88 via the cam member 87. When the cam member 87 is rotated by the driving of the motor 88, the shaft portion 86a of the support member 86 rotates, and the support portion 86b rotates the inlet guide 85 around the rotation axis Ax (see FIGS. 6A and 6B). More specifically, when the inlet guide 85 rotates in a rotation direction in which the downstream end of the inlet guide 85 in the conveying direction D becomes higher, the support portion 86b of the support member 86 presses against the inlet guide 85 to rotate it. On the other hand, when the inlet guide 85 rotates in the opposite direction, as the support portion 86b rotates in a direction away from the inlet guide 85, the inlet guide 85 rotates in the same direction to follow the support portion 86b due to a previously applied biasing force. The inlet guide 85, together with the support member 86, the cam member 87, and the motor 88, is configured to be detachable from the fixing unit 8. Therefore, in the event of damage to the guide surface 85a, toner adhesion, or a malfunction of the support member 86, these can be replaced as a unit.

[0030] The configuration for rotating the inlet guide 85 is not limited to the above. For example, a configuration in which the inlet guide 85 is moved using a solenoid, or a configuration in which the inlet guide 85 is rotated by meshing gears, etc. may also be used. Furthermore, the inlet guide 85 may be rotated directly by a motor, cam, etc., without using the support member 86.

[0031] [Inlet guide rotation control] 6A and 6B are diagrams showing the inlet guide 85 and the support member 86 at a first rotation position P1 and a second rotation position P2, which will be described later. When the image forming apparatus 1 is in operation, the control unit 17 drives the motor 88 and controls the rotation position of the inlet guide about the rotation axis Ax based on the basis weight of the paper S. The basis weight of the paper S is input in advance as a profile setting for the paper S by the user operating the operation unit 11, and is stored in the storage unit 16. Specifically, the control unit 17 controls the rotation position of the entrance guide 85 so that the sheet S enters a position gradually further away from the entrance position Pn of the fixing nip N toward the drive roller 82 as the basis weight of the sheet S decreases.

[0032] The rotational position of the inlet guide 85 may be changed in steps or continuously. For example, in this embodiment, the rotational position of the entrance guide 85 is switched between two stages. When the basis weight of the sheet S is less than 256 g / m^2, the rotational position of the entrance guide 85 is set to the first rotational position P1 (FIG. 6A). The first rotational position P1 is a rotational position where the leading edge of the sheet S contacts the drive roller 82 before entering the fixing nip N. On the other hand, when the basis weight of the sheet S is 256 g / m^2 or more, the rotational position of the entrance guide 85 is changed from the first rotational position P1 to the second rotational position P2 (FIG. 6B). The second rotational position P2 is a rotational position where the leading edge of the sheet S enters a position closer to the fixing nip N (the entrance position Pn of the fixing nip N) than the first rotational position P1. At the first rotational position P1, the vertical distance (height) L1 from the entrance position Pn of the fixing nip N to the leading edge of the entrance guide 85 is approximately 23 mm. At the second rotation position P2, the vertical distance (height) L2 from the entrance position Pn of the fixing nip N to the tip of the entrance guide 85 is approximately 18 mm.

[0033] As a result, when the basis weight of the paper S is small (its rigidity is low), the leading edge of the paper S contacts the drive roller 82 and is conveyed along the drive roller 82 to the fixing nip N. Therefore, the paper S can enter the fixing nip N smoothly without causing paper wrinkles or paper jams. On the other hand, if the paper S has a large basis weight (high rigidity), the paper S will receive an impact when the leading edge of the paper S hits the hard drive roller 82. If the paper S receives an impact, shock noise will occur at the secondary transfer unit 7 in the middle of the paper S, which may cause image unevenness in the direction perpendicular to the conveyance direction D. Therefore, in this case, the rotational position of the entrance guide 85 is changed so that the leading edge of the paper S enters the fixing nip N more directly than when the paper S has a low rigidity. This makes it possible to suppress shock noise at the secondary transfer unit 7. That is, when the stiffness of the paper sheet S is low, the rotational position of the entrance guide 85 is controlled so that the leading edge of the paper sheet S contacts the drive roller 82 at a predetermined angle, for example. As the stiffness of the paper sheet S increases, the rotational position of the entrance guide 85 is controlled so that the entry position of the leading edge of the paper sheet S approaches the fixing nip N. When the stiffness of the paper sheet S is high, the leading edge of the paper sheet S may contact the pressure roller 81 having an elastic layer on its surface.

[0034] The parameter used to control the rotation of the entrance guide 85 may be paper stiffness information relating to the stiffness of the paper S, and may include, for example, at least one of the basis weight, stiffness, and thickness of the paper S. This paper stiffness information may be set (input) in advance by the user operating the operation unit 11, or may be detected by various sensors each time a printing process is performed.

[0035] [Technical effect of this embodiment] As described above, according to this embodiment, the rotational position of the entrance guide 85, which guides the sheet S entering the fixing nip N, around the rotational axis Ax is controlled based on the sheet stiffness information. Therefore, the paper S can be smoothly introduced into the fixing nip N. This reduces image unevenness and paper wrinkles that may occur if the paper S does not smoothly enter the fixing nip N, thereby improving print quality.

[0036] Furthermore, according to this embodiment, when the paper stiffness information is less than the threshold value, the rotational position of the entrance guide 85 is set to a first rotational position P1 where the leading edge of the paper S comes into contact with the drive roller 82 before entering the fixing nip N. On the other hand, when the paper stiffness information is equal to or greater than the threshold value, the rotational position of the entrance guide 85 is set to a second rotational position P2 where the leading edge of the paper S enters a position closer to the fixing nip N than the first rotational position P1. As a result, if the stiffness of the paper sheet S is low, the leading edge of the paper sheet S comes into contact with the drive roller 82 before being transported to the fixing nip N. Therefore, the paper sheet S can enter the fixing nip N smoothly without causing paper wrinkles or paper jams. On the other hand, when the stiffness of the paper S is high, the paper S enters the fixing nip N more directly than when the paper S is at the first rotation position P1. This reduces the impact caused by the leading edge of the paper S hitting the drive roller 82, and reduces image unevenness in the direction perpendicular to the conveyance direction that occurs at the secondary transfer unit 7 due to this impact. Therefore, the print quality can be improved.

[0037] Furthermore, according to this embodiment, the entrance guide 85 is configured to be detachable. This allows the entire inlet guide 85 to be replaced with a new one when the guide surface 85a is damaged or toner adheres to it.

[0038] Furthermore, according to this embodiment, the paper stiffness information is set based on the operation of the operation unit 11 by the user. This allows the user to adjust the rotational position of the entrance guide 85 by appropriately setting the stiffness of the paper S.

[0039] [others] The above describes one embodiment of the present invention, but embodiments to which the present invention can be applied are not limited to the above-described embodiment and its variations, and can be modified as appropriate within the scope of the spirit of the present invention.

[0040] For example, with certain types of paper that are highly rigid, as shown in Figure 7, the paper S may bend immediately after entering the fixing nip N without being able to enter smoothly, causing shock noise in the upstream secondary transfer unit 7. In this case, it may be difficult to eliminate the shock noise by controlling the rotation of the inlet guide 85 described above. In this case, therefore, the nip pressure of the fixing nip N may be reduced, or the transfer pressure of the secondary transfer portion 7 may be increased, or both may be performed. To adjust the nip pressure, for example, the drive roller 82 may be configured to be movable in a direction toward and away from the pressure roller 81. To decrease the nip pressure, the drive roller 82 may be moved away from the pressure roller 81. To adjust the transfer pressure at which the toner image is transferred to the paper S in the secondary transfer unit 7, for example, one of the pair of secondary transfer rollers 71 may be configured to be movable in a direction toward and away from the other. To increase the transfer pressure, the pair of secondary transfer rollers 71 may be moved closer to each other. This adjustment may be performed as necessary, for example, when the user checks the output image quality and determines that image unevenness due to shock noise has occurred. [Explanation of symbols]

[0041] 1. Image forming device 7 Secondary transfer unit (transfer unit) 8 Fixing unit 11 Operation section (setting section) 17 Control Unit 71 Secondary transfer roller 81 Pressure roller (first roller) 82 Drive roller (second roller) 83 Fixing belt 84 Heating roller 84h heating section 85 Entrance Guide 85a Guide surface 86 Support member 86a Shaft 86b Support part 87 Cam member 88 Motor 100 fixing device Ax rotation axis N Fixing nip Pn entrance position P1 First rotation position P2 Second rotation position S paper D Conveying direction R Transport route Y depth direction

Claims

1. A fixing device that applies pressure to a sheet of paper on which a toner image is attached to fix the toner image, A first roller; a second roller facing the first roller to form a fixing nip, the second roller having a surface harder than the first roller; an entrance guide configured to be rotatable about a rotation axis parallel to the second roller and to guide the paper entering the fixing nip; a control unit that controls a rotation position of the inlet guide around the rotation axis based on paper stiffness information relating to the hardness of the paper; A fixing device comprising:

2. the control unit controls the rotation position of the entrance guide so that the leading edge of the paper enters a position that is gradually spaced further toward the second roller than an entrance position of the fixing nip as the paper stiffness information becomes smaller. The fixing device according to claim 1 .

3. The control unit If the paper stiffness information is less than a threshold value, the rotation position of the inlet guide is set to a first rotation position where the leading edge of the paper contacts the second roller before entering the fixing nip; When the sheet stiffness information is equal to or greater than a threshold value, the rotation position of the entrance guide is set to a second rotation position at which the leading edge of the sheet enters a position closer to the fixing nip than the first rotation position. The fixing device according to claim 2 .

4. The paper stiffness information includes at least one of the basis weight, stiffness, and thickness of the paper. The fixing device according to claim 1 .

5. a fixing belt disposed between the first roller and the second roller and forming the fixing nip between the first roller and the second roller; The fixing device according to claim 1 .

6. a heating roller that stretches the fixing belt and heats the fixing belt; The fixing device according to claim 5 .

7. The heating roller has a heating portion provided therein. The fixing device according to claim 6 .

8. a shaft portion parallel to the rotation axis; a support portion provided at one end of the shaft portion and configured to rotate the inlet guide in accordance with rotation of the shaft portion; a cam connected to the other end of the shaft portion and rotating the shaft portion; Equipped with The fixing device according to claim 1 .

9. The inlet guide is configured to be detachable. The fixing device according to claim 1 .

10. The fixing nip is configured to have an adjustable nip pressure. The fixing device according to claim 1 .

11. an image forming unit that forms the toner image; a transfer unit that transfers the toner image formed by the image forming unit onto the paper; The fixing device according to any one of claims 1 to 10, An image forming apparatus comprising:

12. the transfer unit is configured to be able to adjust a transfer pressure for transferring the toner image onto the paper. The image forming apparatus according to claim 11.

13. a setting unit that sets the paper stiffness information based on a user operation; The image forming apparatus according to claim 11.

14. A first roller; a second roller facing the first roller to form a fixing nip, the second roller having a surface harder than the first roller; an entrance guide configured to be rotatable about a rotation axis parallel to the second roller and to guide a sheet entering the fixing nip; A method for controlling a fixing device comprising: a control unit that controls a rotation position of the inlet guide around the rotation axis based on paper stiffness information relating to the hardness of the paper. Control method.

15. A first roller; a second roller facing the first roller to form a fixing nip, the second roller having a surface harder than the first roller; an entrance guide configured to be rotatable about a rotation axis parallel to the second roller and to guide a sheet entering the fixing nip; A control program for a fixing device comprising: a control unit that controls a rotation position of the inlet guide around the rotation axis based on paper stiffness information relating to the hardness of the paper; A control program that functions as a

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