JPS59164566A - Carrying device of original - Google Patents

Abstract

PURPOSE:To reduce the accuracy difference of an original stopping position by arranging two pairs of gear trains having different gear ratio between a driving shaft of a carrying belt and a driving means and engaging/disengaging the two pairs of gear strings by clatches. CONSTITUTION:The gears 31, 32, electromagnetic clatches 33, 34, and electromagnetic brake 35 are engaged with the driving shaft 28 of the carrying belt respectively, the respective gears 31, 32 are supported pivotally around the driving shaft 28 so as to be allowed to rotate relatively and the electromagnetic clatches 33, 34 can be rotated unitedly with the driving shaft 28 through driving pins 36, 37 set up on the driving shaft 28 respectively. The gears 41, 42 unitedly connected to a driving motor 40 are meshed with the gears 31, 32 and driving torque by the driving motor 40 is transmitted from the gear 41 to the gear 31 and from the gear 42 to the gear 32. Said constitution makes it possible to reduce the accuracy difference of an original stopping position.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Use Unexploded IJE accurately supplies a document to an exposure position via a Z conveyor belt placed on a document supply tray, etc. After exposure, the document is placed on a document output tray. σ) relating to a paper feeder for a photocopier that can be ejected.

BACKGROUND ART In a typical copying machine, a document to be copied is positioned and placed on a document table (hereinafter referred to as a platen glass), and a document table cover (hereinafter referred to as a platen glass) is placed on the document table.
After making a copy, opening the platen/C- to take out the original, placing the next original on the platen glass, and repeating the same process, it was difficult to work efficiently when copying a large number of originals. was bad.

On the other hand, with a copying machine equipped with a document feeder, there is no need to repeat the process of manually placing each document one by one on the platen glass, and a large number of documents can be set on the document supply tray. Manual copying operation is possible.

In the document conveying device, it is necessary to stop the document on the conveyor belt accurately at the document exposure position, and conventional stopping means are not used for this purpose. As shown in FIGS. 1 and 2, the leading edge of the document is detected by a sensor S2, and the conveyor belt is stopped in response to the signal.

That is, in the conventional example shown in FIGS. 1 and 2 VC, a platen glass 020 is arranged at the center of the upper surface of an electrophotographic copying machine 01, and a document insertion table 021 and an original output tray 022 are arranged on both sides of the platen glass 020. The original insertion table 02111'I: The insertion roll 023 is not properly placed, and the original P on the original insertion table 021 is inserted into the insertion roller 02.
The platen glass 020 and the nogukyumu chicken bar 0 are inserted into the platen glass 020 by the transport heald 027 which is inserted from the 3VC and spanned between a pair of drive rolls 025 and driven rolls 026 arranged on opposite sides of the cucumber chamber 024.
It is designed to draw you in for 24 hours.

In addition, a drive shaft 028 is disposed on a pair of drive rolls 025K in NU, and a driving shaft 028Vc on the same side is fitted with a gear 029, an electromagnetic clutch 030, and an electromagnetic brake 031.
The gear 029 is pivoted to the drive shaft 028 to allow relative rotation, and the electromagnetic clutch 030 is connected to the drive pin 03.
The electromagnetic brake 031 is connected to the copying machine body 0.
When the electromagnetic brake 031 is activated, the electromagnetic brake 036 is attracted, and the drive shaft 028 is braked by the stopper pin 033 held in the suction plate 036.

, Roughly speaking, the drive motor 034' [the drive gear 035 which is connected to the gear 029] is not meshed with the gear 029, and the drive torque by the drive motor 034 is more than the gear 029 than the gear 035.
9, and when the electromagnetic clutch 030 is energized (electromagnetic clutch 030 is ON), the electromagnetic clutch 0
Clutch plate 029 integrally formed with gear 029 at 30
a is attracted, and the driving torque is applied to the electromagnetic clutch 030.
＼Transmitted to the drive shaft C128 via the drive pin 032,
As a result, the drive roll 025 is driven off and the conveyor belt 0
27 is transported. That is, to explain based on a speed diagram in which the horizontal axis is time t and the vertical axis is speed y in FIG. 3, when the clutch 030 is activated (aJ in FIG. After the document P is conveyed, the leading edge of the document P is detected by the sensor ti-s2 (point b in FIG. 3), the clutch 030 is turned OFF' and the electromagnetic brake U31 is activated, and the conveyor belt 027 is rotated. Please stop (0 point in Figure 3). In FIG. 3, L represents one cycle from the start to the end of conveyance, C1 is the time during which the clutch 0.30 is ON (<, and B is the time during which the brake 031 is ON.

At this time, is the document P stopped at a predetermined position? In this case, the speed of the transport heald 027 is 400 dragons/sec.
If it is up to about c, the stopping position accuracy can be within ±0.5 mtnW degrees, and there is no problem in practical use as a self-photography system.

However, as the speed of the copying system increases, it becomes necessary to increase the conveyance speed at the same time. However, as the general conveyance belt speed increases to 1000 to 2000 mm/sec, the stop position error will decrease from the conventional 2. There was a drawback that it increased by 5 times to 5 times. This is G-1 conveyor belt 0
The speed of 27 is Vmm/sea\electromagnetic clutch O: ri0 and the variation in response time of electromagnetic brake 031 is Δts.
This is because, if ec, the original stopping position is expressed by ΔL−VXΔt−. In other words, the transport bell) 027 (h
The stop position i error increases in proportion to the speed.

OBJECTS OF THE INVENTION The present invention relates to an improvement of the document conveying device 1 that eliminates the above-mentioned drawbacks. The object of the present invention is to provide a document conveying device that can reduce accuracy errors as much as possible.

Constituent structure of the invention Two sets of gear trains having different VC gear ratios are interposed between the drive shaft of the conveyor belt for transporting the manuscript over the platen glass and the drive means. By engaging and disengaging the clutch, the transport speed of the transport belt can be selected from multiple stages.If the transport speed of the transport belt can be stopped from a low state, it is possible to improve the accuracy of the original stopping position. Be able to do it.

Practical Example The present invention will be explained below with reference to FIGS. 4 to 13.

Reference numeral 1 designates the main body of the electrophotographic copying machine. A drum-shaped photoreceptor 2 is disposed within the main body 1 of the electrophotographic copying machine so as to be rotationally driven by a motor (not shown).
, a transfer peeler 5 and a cleaning device 6 are arranged along the rotational direction of the drum-shaped photoreceptor 2.

Mar = H photo bridge body 1 has a platen glass 20 on the center top surface
A lamp 7 is arranged below the right end of the platen glass 20, and mirrors 18, 9, and 10 are arranged side by side on the right side, and an exposure lens 11 is arranged to the left of the mirror 10. , the mirrors 12 are arranged W 2
The bias of the original that has been overexposed by the lamp 7 is imaged on the drum-shaped photoreceptor 2 via the mirror 8, 9, 10, 12 and the exposure lens 7.

Roughly below the left side of the drum-shaped photoreceptor 2 [a paper feed bag 1a13 is placed, and the paper 14 is sent from the paper feeder 13 between the photoreceptor 2 and the transfer peeling device 5, and the toner formed on the photoreceptor 2 After the image is transferred to the paper 1/1 and fixed by the fixing device 15, it is discharged onto the paper tray 10 for the first time.

Also, as shown in Figures 4 and 5,
Similarly to the conventional example shown in Fig. 2, the platen glass 20
A document insertion table 21 and a document ejection tray 22 are arranged on the side of 1Tlil, and an insertion roll 23 is provided on the document insertion table 21.
・The original P on the original insertion table 21 is inserted by the insertion roll and moved to the vacuum chamber 24).
O is drawn into the platen glass 2o and the vacuum chamber 24 by a conveyor belt 27 stretched between a pair of driving rolls 5 and driven rolls 2G disposed on opposite sides. A fan (not shown) is interposed therein, and the outer wall of the vacuum chamber 24 is provided with a suction hole (vc) in the portion that contacts the conveyor belt 27, and the conveyor belt (27) is also provided with a suction hole. ing. Therefore, by suctioning outside air from the transport heald 27 and the vacuum chamber σ)9fDg, the transport belt 27 is given the ability to attract the document P.

As shown in FIGS. 6 and 7, a drive @28 is provided extending integrally with the drive roll 25,
The drive shaft 28 is connected via a bearing 29.
Ray-A 30 VC Rotatably supported. ing.

The drive shaft 28, VC gear 31, 32, electromagnetic clutch 3
3.34 and electromagnetic brake 35 are respectively fitted, gears 31 and 32 are pivoted to allow relative rotation with respect to the drive shaft A, and electromagnetic clutch 33
．． 34 are drive shafts 28 K and drive bins 3 installed vertically.
It is designed to be rotated integrally with the drive shaft path through 6.3'7. The electromagnetic brake 35 is fixed to the frame 30, and when the electromagnetic brake 35 is activated, the suction plate 3
8 is attracted, and the drive shaft 28 is braked by the brake pin 39Vc engaged with the suction plate 3SVc.

The front dead tooth il+ 31 and the gear 32 are each equipped with four gears 41\42 which are integrally connected to a drive motor 40. The looseness is transmitted from the gear 42 to the gear 32. When the electromagnetic clutch 33 is in operation (energized), the clutch plate 32a integrally formed with the gear 32 is connected to the electromagnetic clutch 33.
3, the drive torque G (11) is transmitted to the drive shaft 28 via the electromagnetic clutch 33 and the drive pin 37. Further, when the electromagnetic clutch 34 is activated, the clutch plate 31a integrally formed with the gear 31K
However, the same electromagnetic clutch 34 K is sucked, and the drive motor 40
The drive torque transmitted to the gear 31K is transmitted to the drive shaft via the same electromagnetic clutch 34 and the drive pin 36. Also, the drive shaft 40aVc of the drive motor 40 has a slit. Several encoder disks 43 are formed, and a photo sensor 44 is disposed between the encoder disks 43 so that the rotation speed of the drive motor 40 is detected by the encoder disk 43 and the photo sensor 44. It has become.

Since the embodiments shown in FIGS. 4 to 7 are constructed as described above, the original P on the original insertion table 2 is 0.
Feed from insertion roll 23vc) 45K
After correcting the skew timing, send it out in the direction of the platen glass 20. At this time, since the electromagnetic clutch 33 is operating, the drive shaft 28 is rotationally driven by the drive motor 4o. Therefore, 76% of the raw material sent out from the cage 45 is transferred to the conveyor belt (271C) via the vacuum chamber 24 and absorbed into the platen glass 20.
1Y conveyance λ', the tip force X sensor S, VC of document P
Detected from g, l'1. , b and - the operation of the magnetizing launch 33 is released and becomes OFF state - the clutch plate 32 a is separated from the electromagnetic clutch 33 and at the same time as λt, 1. + is the magnetic clutch;))/1 is activated and becomes ON (')/ton (d clutch 3/I and clutch plate 31
a has been retained.This time, the I
The drive shaft 28 is driven.

Therefore, the speed of the conveyor belt 27 should be changed from V, gm/sec to v2m71 /sec Vc. That is, until the document P is detected by the document P or ten → dog-8, the conveyance of the conveyor belt 27 is 1ffl + qm/'.
It is in the 1°, -δ series of sec, and the same sen → j-7S.

After it is detected, the conveyance speed of the &-1 conveyor belt 27 is in the low speed range of V2mm7'sec. In this example, I/) is V, = 1000 to 2000 mm/
It is set to about sec, v2=100wn/sec
It is set to IJF. Then, the document P is conveyed at the speed of ■2, and now the sensor S1
When the leading edge of the document P is detected by the sensor S2 located closer to the conveyance side, the electromagnetic clutch 34 is deactivated after a certain period of time and becomes OFF.The clutch plate 31a is separated from the electromagnetic clutch 34 and the electromagnetic brake 35 is activated, the driving port 25 and the conveyor belt 27 are stopped, and the original P is stopped exactly at the original exposure position, and after the exposure is completed,
The conveyor belt 27 sends the document P to the discharge tray 22 and suspends it.

The above operation will be explained with reference to FIG. 8, a speed diagram in which the horizontal axis represents time t and the vertical axis represents the conveying speed 2 of the conveying belt 27.

In FIG. 8, L represents one cycle from the start to the end of conveyance of the document P, and C2 represents when the clutch 34 is ON.
Assume that C2 represents the time Y during which the clutch 33 is ON, E represents the time 7 during which the brake is ON, and -85 represents the time 7 during which the clutch 33 is ON. In addition, in the velocity diagram in the other σ) embodiments, O, B are the same.

In FIG. 8, the drive motor 40 is always ON and in a rotating state. First, the electromagnetic clutch 33 is activated (point a in FIG. 8), the conveyor belt 27 gradually increases in speed, and then the speed When V1 is reached, the document P is conveyed and the leading edge of the document P is detected by the sensor S.
1 is detected (point b in FIG. 8), the clutch 33 is disengaged, and at the same time, the sleeper flake 35 is activated to brake the conveyor belt 27 and stop the conveyor belt 27. [IV3] After a while, the electromagnetic clutch 311 is activated (point 0 in Fig. 8) and the document is transported to the transport heald 27 at a speed of ■2, and the document is now Hz 6-1 and the sensor S2 is pointing the document Pσ) first! 71
When the electromagnetic clutch 34 disengages after a certain period of time (point 0 in Fig. 8), the electromagnetic brake 35 operates again and stops the conveyor belt 27. One cycle is completed by accurately arranging te, j, k5, and p at the original exposure position (point f in FIG. 8). Thus, in this embodiment 1911, gears 32,
．． Two sets of gear trains, a gear train with a tooth ratio of 1 and a gear train with a tooth ratio of 1□ from gear 31 to 41, should be conveyed. Dressing/
Power transmission between these two sets of gear trains′? :Electromagnetic clutch 3
3. By switching by engaging and disengaging in step 34, the conveying speed of the conveying belt 27 can be set in two stages, Vl and V2, and the difference in accuracy of the document stopping position can be reduced. That is, by switching the conveyance speed of the conveyor belt 27 from Vl (high speed) to V2 (low speed) K, if the variation in response time of the electromagnetic clutch 34 and electromagnetic brake 35 is Δtsec, the document stop error is Δt=V2Δt.
You can do that. Therefore, compared to the conventional document feeder which cannot change the feed speed, the precision error of the document stop position can be reduced by 2/v, vc.

In the embodiment shown in FIGS. 4 to 8, the electromagnetic clutches 33, 34 are arranged in series on the drive shaft 28. However, as shown in FIG. The gear 32 is meshed with the gear 42, and the gear 32 is connected to the intermediate shaft 4.
6, and the intermediate shaft 46 has a VC electric clutch 3.
1 and a gear 41 are arranged. The gear 11 is integrally connected to the intermediate shaft 46vC, and the gear 32 is pivotally supported with respect to the intermediate shaft 46 so as to be allowed to rotate relative to the intermediate shaft 46vC. Further, the electromagnetic clutch 34 has a drive pin 3 erected on the intermediate shaft 46.
6, it is configured to rotate integrally with the intermediate shaft 46. Note that the intermediate shaft 46 is pivotally supported by the frame 30 via a bearing (not shown).

Further, the gear 321='j is meshed with the gear 31 pivotally supported on the drive shaft 28, and the gear 41 is out of mesh with the gear 47Vc.

A Vc electromagnetic clutch 33 and an electromagnetic flare 35 are provided on the drive shaft.

1] The input gear 47 is integrally connected to the drive shaft 28Vc, and the gear 31 is pivotally supported to allow relative rotation with respect to the drive shaft 28Vc.

Since the embodiment shown in FIG. 9 is configured as described above, the drive torque of the drive motor 40 is transmitted from the gear /I2 to the gear 32, and when the electromagnetic clutch 34 is in the OFF state, the gear 32 becomes an idler. If the driving torque is transmitted to the gear 31 and the electromagnetic clutch 33 is in the ON state, the drive! The drive shaft 28 is rotated through the pin 37.

Further, if the electromagnetic clutch 34 is in the ON state, the drive pin 3
The intermediate shaft 46 is rotationally driven through the gear 6, and the drive shaft 28 is rotated by the driving torque transmitted to the gear 47 through the gear 41.

In this way, in this embodiment, a gear train with a tooth number ratio i consisting of gear 42, gear 32, and gear 31, and gear 42,
Teeth ratio i2 consisting of gear 32, gear 41, and gear 47
Two sets of gear trains are interposed between the drive roller 5 and the drive motor 40, which move the conveyor belt 27. By switching by engaging and disengaging 34, the conveying speed of the conveying belt 27 can be set in two stages, 1 and V2. It is possible to obtain the same effects as in FIGS. 4 to 8. Note that the speed diagram of the conveying speed V and time t is exactly the same as that in FIG. 8.

In the embodiments shown in FIGS. 4 to 9, two electromagnetic clutches are used to engage and disengage as appropriate, but even if a one-way clutch 51 is used as shown in FIG. good. That is, the gear 42 directly connected to the drive motor 40 meshes with the K gear 32, and the gear 32 engages with the intermediate shaft 4.
6, and an electromagnetic clutch 34 and a gear 41 are disposed on the intermediate shaft 46. The gear 41 is integrally connected to the intermediate shaft 46, and the gear 32 is pivotally supported by relative rotation to the intermediate shaft 46.

Further, the gear 41 is meshed with a gear 47 pivotally supported on the drive shaft path via a one-way clutch 51.

The one-way clutch 51 is designed to allow torque transmission in only one direction, and in this case, it only allows torque transmission from the mackerel wheel 47 to the drive shaft 288.
Torque transmission from the side to the gear 47 side can be cut off.

On the other hand, the drive motor l+0 has drive shafts 40a disposed on both sides, and a gear 48 is integrally connected to the opposite side of the gear 42, and the gear 48 is meshed with the gear 49, The workpiece 49 is integrally connected to the drive shaft 28, and! The gear 50 is not meshed properly. In addition, IA is shown in Figures 4 to 9.
In the embodiment shown, the drive motor 40 continuously rotates in the ON state during one cycle, but in the embodiment shown in FIG. ing.

Since the embodiment shown in FIG. 10 is configured as described above, the drive motor 40 is first turned on and the drive motor 40 is turned on at point a in FIG. 11, as shown in FIG. ), the drive torque of the drive motor 40 is transmitted from the gear 42 to the gear 32 V (at this time, the electromagnetic clutch 34 is turned on at the same time as the drive motor 40) (point a in Figure i 11), so the electromagnetic The intermediate shaft 46 is driven via the clutch 34 and the drive pin 36, and the gear 41
The drive shaft 28 is then driven by the one-way clutch 51 via the gear 47. Then, the transport bay L 27 gradually increases its speed and eventually reaches the speed V, transports the original P, and transports the original P.
When sensor S1 detects the tip of (point b in Figure 11)
, the clutch 34 disengages, the drive shaft 28 gradually decelerates, and the speed of the conveyor belt 27 reaches ■2Vc (0 in Fig. 11).
point), and when the speed reaches V2, the current high i' is \gear 48
, the IW drive torque of the drive motor 4o is transmitted to the gear 5o via the gear 49 (the same gear 49 is the eye 5-)Y, and the conveyor belt 27' x fJs continues conveyance at a low speed of 2 degrees.Next, the sensor s2 When the tip of the document P is captured (point d in Fig. 11), the drive motor 4
Stop at 0 (point 0 in Figure 11). and conveyor belt 2
7 is stopped, the document P is placed exactly at the document exposure yc7 position, and one cycle is completed (rhf point in the first figure). Note that M in FIG. 11 indicates the time during which the drive motor 4o is ON.

In this way, in the non-example, the gear 42, the gear 32,
Teeth, wheel 41 and gear 47 have a gear ratio iIo and a gear train consisting of gears 48, 49 and 50 have a gear ratio 1
Two sets of gear trains are interposed between the drive roll 25 that drives the conveyor belt 27 and the drive motor 40, and power transmission between these two sets of gear trains is performed by engaging and disengaging the electromagnetic clutch 34 and the one-way clutch 51. By switching from D to D, the conveying speed of the conveying belt 27 can be set to two stages (1 and 2), and the same effect 7 as that of the embodiment shown in FIGS. 4 to 9 can be obtained. can.

Furthermore, in this embodiment, by using the one-way clutch 51, the conveying speed of the conveying belt 27 can be smoothly shifted from V1 to V2.

Zara VC In the example VC shown in FIG. 12, the first
Figure 0L/CAlthough the configuration is almost the same as the illustrated embodiment,・
The difference is that a one-way clutch 51 is interposed between the gear 50 and the drive shaft 28, an electromagnetic brake 35 is disposed above the drive shaft, and the drive motor 40Y is operated in a constant ON state during one cycle.

In the embodiment shown in FIG. 12, the conveyance speed V and the velocity diagram over time are as shown in FIG.
In this state, the drive torque is transmitted to the gear 50 via the gears 48 and 49, drives the drive shaft 28 via the one-way clutch 51, and moves the transport heald 27 at a low speed v2.
The conveyance continues at the 13th (bad point a) 0 and the electromagnetic clutch 34 turns ON. - Drive torque is transmitted from the gear 42 to the electromagnetic clutch 34 via the gear 32, and the drive pin 36 is The gear 47 is rotationally driven from the intermediate shaft 46 through the gear 41, and the drive shaft 28 is driven by the drive torque transmitted from the gear 47 side.
point), gradually increases the speed of the conveyor belt 27, and eventually reaches the speed V1.
When the document P is conveyed at a speed V1 and the sensor S1 detects the leading edge of the document P (point 0 in FIG. 13), the clutch 34 disengages, the drive shaft path gradually decelerates, and the conveyor belt The speed of No. 27 reaches v2Vc (point d in FIG. 13). The conveyance continues roughly, and then the sensor S2 detects the leading edge of the document P (point 0 in FIG. 13), and after a certain period of time [the electromagnetic brake 35 is not activated and point f in FIG. 13], the conveyor belt 27 The brake 35 is braked, the conveyor belt 27 is stopped, the original P is placed at the original exposure position, and after the exposure is completed, the brake 35 is released (point 8 in Figure 13), reaching point h and completing one cycle. is completed〇In this way, the embodiment V illustrated in FIGS. 12 and 13
Also in C, a gear train with a gear ratio i1 consisting of gear 42, gear 32\gear 41, and gear 47, and gear 48, gear 49
and 'Two sets of gear trains with a tooth ratio of 12 consisting of gears 50 and 50 are interposed between the drive roll 25 that drives the conveyor belt 27 and the drive motor 40 to transmit power between these two sets of gear trains. The engagement and disengagement of the electromagnetic clutch 34 and the one-way clutch 51
You can expect the same operation and effect as the embodiments shown in Figures 14 to 11.

As is clear from the description of the embodiments, beyond the effects of the invention, there are
Two sets of gear trains with different tooth ratios σ) are interposed between the drive shaft of the conveyor belt that transports the document over the platen glass and the drive means, and the two sets of gear trains 7 are engaged by at least one clutch. Since the belt has been removed, the conveyance registration level of the storage belt can be set to a higher level, and the accuracy of the document stopping position can be aggravated.

[Brief explanation of the drawing]

11 to 6 is a schematic front view of a conventional document conveyance device, FIG. 2 is a plan view thereof, FIG. 3 is a speed diagram thereof, and FIG. 4 is an electrophotographic copying machine using the document conveyance device according to the present invention. Fig. 5 is a schematic front view illustrating an embodiment of the document conveying device according to the present invention. Fig. 6 is a plan view thereof. Fig. 7 is a longitudinal sectional view of the main part. Figure 8 is the speed diagram/
FIG. 9 is a plan view of another embodiment; FIG. 10 is a plan view of yet another embodiment; FIG. 11 is a velocity diagram thereof; FIG. 12 is a plan view of yet another embodiment; FIG. 13 shows the velocity diagram. l...electrophotographic copying machine main body, 2...drum-shaped photoreceptor,
3... Charger, 4... Developer, 5 - Transfer peeler,
6... Cleaner, 7... Lamp, 8.9.1o... Mirror, 11... Exposure lens, 12... Mirror, 13
. . . Paper feed device, 111 . ) Ejection tray, 23... Insertion roll, 24-way transfer roll, Uta... Drive roll, 26... Driven roll, 27
... Conveyor belt, 28 ... Drive shaft, 29 ... Bearing, 30 ... Brake pin, 40 ... Drive motor, 41.42 ... Gear, 113 Encoder disk,
44...Photo sensor, 45...Gate, 46...
Intermediate shaft, 47.48.49.50...gear, 51...
One-way clutch. Agent Ben L11 Officer Ebara Nozomi 1 Atsushi 1 Figure 26 Koma 2 Figure 9 Basu 10 prisoners

Claims (1)

[Claims] In a document conveyance device of a copying machine equipped with a conveyance belt for conveying a document over a platen glass, two sets of gear trains having different tooth ratios are interposed between the drive shaft of the conveyance belt and the drive means. A document conveying device characterized in that two sets of gear trains are engaged and disengaged by at least one clutch.