Developing unit causes toner to stick to the surface of the photosensitive drum.

Developing Unit

Purpose: Here, you will learn about the construction of the developing unit together with its functions and the mechanism used to detect faults associated with it.

　

　

1. Outline

a Function

The developing unit serves to turn a static image on the photosensitive drum into a visible image using toner supplied from the toner bottle.

b. Construction

The developing unit consists of a developing cylinder, toner stirring plate, and toner feedscrew.

These parts rotate or move by the work of the drive coming from the main motor by way of the developing clutch.

The toner inside the developing unit comes from the toner bottle by way of the sub hopper. When the sub hopper feedscrew motor (M12) rotates the toner feedscrew, the toner inside the sub hopper is forwarded to the developing unit.

The developing unit and the parts around the unit are arranged as shown in the following diagrams:

　

○Developing Unit and Parts Around It [1] Toner bottle [2] Sub hopper [3] Toner feedscrew [4] Developing unit [5] Developing assembly toner sensor (TS1) [6] Sub hopper toner sensor (TS2) Developing Unit c. Functions The machine uses the following control mechanisms in relation to the developing unit: ∙ toner supply control, in which toner is sent from the toner bottle to the sub hopper and then to the developing unit in sequence. ∙ toner detection, in which the inside of the developing unit and the sub hopper is checked for the presence/absence of toner to impose a limit on the amount of toner to be supplied. ∙ toner level detection, in which the level of toner remaining inside the machine is checked. 　 Now, let’s take a look at the individual functions of the developing unit. 　 　 2. Toner Supply Control a. Outline The machine is designed to supply toner in response to a shortage of toner inside the developing unit and in amounts needed. When a shortage of toner occurs inside the developing unit, a required amount is sent from the sub hopper to the developing unit. In the event of a shortage of toner inside the sub hopper, on the other hand, a required amount is also sent from the toner bottle to the sub hopper. b. Timing of Execution sub hopper: when the DC controller detects the absence of toner inside the sub hopper. developing unit: when the DC controller detects the absence of toner inside the developing unit. 　 c. Mechanism of Control The DC controller rotates the feedscrew used to move toner to the sub hopper or the developing unit. ∙ for the sub hopper, the bottle rotation motor (M5) is rotated intermittently (a single cycle consisting of 3 sec of rotation and 2 sec of suspension). ∙ for the developing unit, the sub hopper feedscrew motor (M12) is rotated intermittently (a single cycle consisting of 1 sec of rotation and 1 sec of suspension). 3. Toner Detection a. Outline The machine is designed to check the inside of the sub hopper and the developing unit for the presence/absence of toner so that it may supply toner in amounts that are required. 　 b. Timing of Detection ∙ for the sub hopper, as necessary. ∙ for the developing unit, when the developing clutch (CL3) is driven. 　 c. Method of Detection The DC controller monitors the output of the 2 toner sensors (TS1, the developing unit toner sensor; TS2, sub hopper toner sensor) found inside the developing unit and the sub hopper at intervals of 100 msec. ∙ Sub Hopper The machine will assume the presence of toner if the output of TS2 indicates presence 2 times or more continuously (200 msec). The machine will assume the absence of toner if the output of TS2 indicates absence 100 times or more continuously (10 sec). ∙ Developing Unit The machine will assume the presence of toner if the output of TS1 indicates presence 7 times or more among the 25 checks (2.5 sec). (in the case of low-speed mode, 12 times out of 42 times) The machine will assume the absence of toner if the output of TS1 indicates absence less than 7 times among the 25 checks (2.5 sec). (in the case of low-speed mode, less than 12 times out of 42 times) d. Machine Response   When the DC controller detects the absence of toner inside the sub hopper or the developing unit, it executes toner supply control.   As it executes toner supply control, the DC controller also checks the level of toner, issuing to the main controller a toner absent error according to the level of toner inside the machine. 　 　 4. Toner Level Detection a. Outline The machine checks the level of toner remaining inside it to issue an error message, thereby alerting and prompting the user to replace the toner bottle. b. Timing of Detection The machine checks the level of toner remaining inside it when the DC controller detects the absence of toner in the sub hopper or the developing unit. 　 c. Method of Detection The DC controller keeps track of the number of intermittent rotations made by the supply motor after the absence of toner has been detected; when the count reaches a specific number, it will assume that the toner inside the machine is limited or is entirely absent. If a supply of toner arrives before the count reaches a specific number and, as a result, the presence of toner is detected, its counter reading will be reset. ∙ Sub Hopper: The machine will assume that the level of toner inside the sub hopper and the toner bottle is limited when the toner bottle rotation motor has made 20 intermittent rotations continuously (100 sec). -> toner level alert ∙ Developing Unit:　 The machine will assume that the toner inside the developing unit, sub hopper, and toner bottle is gone when the sub hopper feedscrew has made 200 intermittent rotations continuously (400 sec). -> toner absent error 　 d. Machine Response ∙ In the event of a low toner level, the machine will indicate a warming message to alert the user to a possible shortage of toner and disable printing operation. ∙ In the event of the absence of toner, the machine will indicate an error message to prompt the user to replace the toner cartridge and disable printing operation. 　 Toner Absent Error Screen 5. Recovery Sequence The machine is not equipped with a means of finding out whether or not its toner bottle has been replaced. It will assume that the toner cartridge has been replaced in response to the following and run recovery sequence: 1. the front cover has been opened/closed after a toner level warning or a toner absent error is detected. 2. the machine has been turned off and then on after a toner level warning or a toner absent error is detected. The recovery sequence consists of the following: 1) the machine rotates the toner bottle rotation motor (intermittent; ON for 3 sec, OFF for 2 sec). 2) if the sub hopper toner sensor detects the “presence of toner,” the machine ends the recovery sequence. 3) if the sub hopper sensor does not detect the “presence of toner” after 20 intermittent rotations (100 sec) of step 1), the machine will stop the toner bottle rotation motor and indicate the error message once again. If the toner bottle rotation motor (M5) is out of order, the machine will not be able to send toner from the toner bottle to the sub hopper. If a toner absent error still occurs after replacing the toner bottle with a new one, there is a likelihood of a fault in the toner bottle rotation motor (M5). 6. Detecting a Fault in the Toner Feedscrew a. Outline The machine has a mechanism to check for clogging in the toner supply path connecting to the sub hopper to the developing unit, possibly caused by a fault in the toner feedscrew. b. Conditions The sub hopper is found to be without toner, and the sub hopper feedscrew motor is rotated 100 times (intermittent); however, the presence of toner is not detected in the developing unit. c. Cause of a Fault 1) fault in the sub hopper feedscrew motor (M12). 2) damage on the toner feedscrew or its drive parts. 3) fault in the developing unit toner sensor (TS1) or the sub hopper toner sensor (TS2). 　 d. Machine Response The machine will indicate an error code (‘E020-0000’) and disable printing operation. [1] Developing cylinder [2] Toner stirring plate [3] Toner feedscrew [4] Toner supply mouth [5] Developing assembly toner sensor (TS1)