JPH03214862A - Image reader - Google Patents

Abstract

PURPOSE:To drive an image reader with less speed variance by adding an external additional element like a mechanical damper to the scanner only in a specific area of the speed range corresponding to a read magnification and disconnecting the external additional element in the other speed area. CONSTITUTION:When the output of a speed setter 75 rises, a drive circuit 76 turns on or off a clutch 23 in accordance with the set speed of a speed set signal supplied from the speed setter 75. When the moving speed of an optical system is low, a mechanical damper 24 is connected to a stepping motor 12 to increase the moment of load inertia of the optical system, namely, the stepping motor 12, and the optical system is smoothly driven to considerably reduce the peak of a high frequency component. When the moving speed of the optical system is high, the mechanical damper 24 can reduce the moment of load inertia of the stepping motor 12, and a bad influence upon the rise characteristic is prevented.

Description

[Detailed Description of the Invention] [Purpose of the Invention (Industrial Application Field) This invention reads a document placed on a document table, for example, and outputs the read image signal to an external device such as a computer. The present invention relates to an image reading device.

(Prior Art) As is well known, stepping motors have been used as scanning means of image input devices because they can be easily driven by digital signals and can be easily positioned with high accuracy while being oven loop controlled. By the way, when driving a stepping motor over a wide speed range, in the low speed range, the rotor inside the stepping motor moves stepwise, causing speed fluctuations, and in the high speed range, there is no stepwise movement due to a decrease in frequency response characteristics. Speed fluctuations occur due to variations in output torque between excitation phases. This speed fluctuation will be further explained using FIG. 14. FIG. 14 shows the relationship between the driving speed and speed fluctuation of the stepping motor. The speed fluctuations are particularly large in the low speed range, and as the speed increases, the speed fluctuations become smaller.

As a means of reducing speed fluctuations inherent to the stepping motor, variable pulse control has been proposed in which the time interval at which excitation of the stepping motor is switched is periodically varied in response to the fluctuations. At this time, speed fluctuations can be reduced by increasing the load moment of inertia by using an external load element such as a mechanical damper. FIG. 15 shows the relationship between the driving speed and output torque of the stepping motor. As is clear from FIG. 15, when the motor is driven at high speed, the torque decreases, and when an external load element with large load inertia is used, the start-up characteristics at high speed often deteriorate or step out occurs. Furthermore, as described above, the stepping motor has small speed fluctuations in the high-speed range and can provide sufficient performance without adding any external load elements. As described above, the external load element has a great effect on reducing speed fluctuations in a low speed range, but has a problem in that it has a negative effect in a high speed range.

(Problems to be Solved by the Invention) As described above, in the conventional image reading device, when an external load element is added to the stepping motor, the start-up characteristic deteriorates in the high-speed range or the step-out occurs.

Therefore, the present invention provides an image reading device that is not affected by the load inertia of a mechanical damper even in a region where the torque of a stepping motor decreases, and that prevents deterioration of start-up characteristics and step-out in a high-speed region. The purpose is to

[Structure of the Invention] (Means for Solving the Problem) The image reading device of the present invention includes a reading means for reading an image, an instruction means for instructing the reading magnification of the image read by the reading means, and an instruction means for instructing the reading means to read the image. a scanning means for scanning at a speed corresponding to the reading magnification instructed by the means; a stepping motor for driving the scanning means; an external load element for imparting a load moment of inertia to the stepping motor; and connecting means for connecting the external load element to the stepping motor during a predetermined speed range.

(Function) This invention has a structure in which an external additional element such as a mechanical damper is added to the scanning means only in a specific region of the speed range corresponding to the reading magnification, and the external additional element is separated from the scanning means in other speed regions. That is.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 2 shows a scanner as an image reading apparatus of the present invention, which reads a document and outputs the read image signal to an external device such as a computer.

That is, 1 is a scanner body, and an operation panel (not shown) is provided at the upper front part of this body 1. A document mounting table (platen glass) 2 made of transparent glass is fixed to the upper surface of the main body 1. A document cover 1a that can be opened and closed is provided near the document table 2. As shown in FIG. The original O placed on the original table 2 is
An optical system 3 consisting of an exposure lamp 4 and mirrors 5, 6, and 7 reciprocates in the direction of arrow a along the lower surface of the document table 2, thereby performing exposure scanning during the reciprocation. In this case, mirrors 6 and 7 move at half the speed of mirror 5 so as to maintain the optical exposure length. The light reflected from the original by the scanning of the optical system 3, that is, the light reflected from the original O by the light irradiation of the exposure lamp 4, is reflected by the mirrors 5, 6, and 7, passes through the variable magnification lens block 8, and is arranged in a column. The document O is guided to a line sensor 9 having a plurality of light receiving elements (CCD) arranged in a shape, and an image of the document O is formed on the surface of the line sensor 9.

FIG. 3 shows a drive mechanism for moving the optical system 3 back and forth. That is, mirror 5 and exposure lamp 4
is supported by a first carriage lla, and mirrors 6 and 7 are supported by a second carriage llb, and these first and second carriages 118111b are guided by a guide rail (not shown) and are movable in parallel in the direction of arrow a. There is. That is, the stepping motor 12 drives the fixed shafts 15 of the pulleys 14, 14 via the transmission mechanism 13. This booli 1
The rotations of 4 and 14 are transmitted to the carriages lla and llb via transmission belts 16 and 16, respectively. The transmission belts 16, 16 each have one end 16
A is fixed to the scanner body 1, and a booby 17 is rotatably provided from one end 16A to the second carriage 1lb.
, the pulley 14, the idler pulley 18, and the second carriage llb via a pulley 19 rotatably provided, and the other end 16B is connected via a spring 20 to which a constant tension is applied. It is fixed to the main body 1. A first carriage ll that supports the mirror 5 between the middle part 16a of the transmission belt 16, that is, the pulley 17 and the pulley 14
One end of a is fixed. Therefore, when the stepping motor 12 rotates, the rotation is transferred to the transmission belt 16 via the transmission mechanism 13, the fixing member 15, and the pulley 14.
, the transmission belt 16 moves, the first carriage lla moves, and along with that, the second carriage lla moves.
b also moves. At this time, since the bogies 17 and 19 serve as movable pulleys, the second carriage 1lb moves in the same direction at 1/2 the speed of the first carriage lla.

Note that the moving directions of the first and second carriages lla and llb are controlled by switching the rotational direction of the stepping motor 12.

In addition, a mechanical damper (external load element) 2 is connected to the stepping motor 12 via a clutch (connection means) 23.
4 are connected. As a result, mechanical damper 2
4 is connected to or disconnected from the stepping motor 12 by turning the clutch 23 on or off.

Further, the first carriage lla is moved to a predetermined position (home position according to the magnification) by driving the stepping motor 12 according to the size of the original O and the reading magnification. Then, when the start of reading is instructed, the first carriage lla first moves to the second carriage lla.
The carriage is moved in the direction of the carriage 1lb, and then the exposure lamp 4 is turned on and the carriage is moved in the direction away from the second carriage Ilb. When scanning of original O is completed, exposure lamp 4
is turned off, and the first carriage lla is returned to the home position.

Further, a detector 21 for detecting movement of the first carriage lla to the home position;
Detector 22 that detects movement of a to the limit position
, 22 are provided.

FIG. 1 schematically shows the overall control system.

In other words, CPtT30 as a control unit that controls the whole
is the internal bus 31 and each input/output section 3 2 a %
3 2 b s 3 2 c s 3 2 d s
3 2 e and 32 f to an interface circuit 33, an image processing circuit 34, an inverter circuit 35 with dimming,
the motor drive circuit 36, the detector group 21, 22, 22,
and an operation panel 37 having a display section.

The image processing circuit 34 performs image processing on the read signal supplied from the line sensor 9 via the A/D conversion circuit 38. The image signal subjected to this image processing is outputted as a reading result to the external device 40 via the interface circuit 33. The light control inverter circuit 35 detects the amount of light from the exposure lamp 4 on the detector 3.
The light is adjusted based on the detection output of 5a. The motor drive circuit 36 rotates the stepping motor 12 at a plurality of speeds corresponding to the reading magnification. The operation panel 37 is used to input multiple instructions or display multiple statuses.

The line sensor 9 is driven and controlled by a CCD driver 39.

Next, the configuration of the stepping motor 12 and its motor drive circuit 36 will be explained using FIGS. 4 to 8. That is, the stepping motor 12 is a hybrid type (same polarity type) five-phase stepping motor,
It is composed of a rotor 51 and a stator 52. The rotor 51 is connected to a mass-balanced rotating load (not shown).

As shown in FIG. 4, the rotor 51 includes a shaft 53 made of a non-magnetic material, a permanent magnet 54 attached to the outer periphery of the shaft 53 and magnetized in the axial direction, and both ends of the permanent magnet 54. It is composed of toothed cups 55a and 155b made of a magnetic material and each attached in a cap shape from the side. In this example, 50 small teeth 56 are formed at equal pitches in the circumferential direction on the gear cutting force pad 55a155t). The small teeth 56 on the gear cup 55a side and the small south 56 on the gear cup 55b side are provided with a 1/2 pitch difference in the circumferential direction.

On the other hand, the stator 52 is connected to the rotor 5 as shown in FIG.
1, ten salient stator poles 58 protruding from the inner surface of the stator core 57, and small teeth 59 provided at equal pitches at the tips of these salient stator poles 58. , and an excitation winding 60 wound around the stator salient poles 50. The excitation windings 60 are connected in series or in parallel to each other in the stator salient poles 58 facing each other, so that the five excitation phases A. There are 5 different varieties, classified into BSCSD and E.

As shown in FIG. 6, the motor drive circuit 36 is broadly divided into an excitation circuit 71, a distribution circuit 72, and a storage circuit 73.
, an arithmetic circuit 74 , a speed setting device 75 , and a drive circuit 76 .

As shown in FIG. 7, the excitation circuit 71 connects both ends of the excitation windings constituting each excitation phase to the power 1 transistor 6.
1 and 62 to the power supply lines 63 and 64, and turn on the power transistors located diagonally in order.
When turned off, a positive or negative current flows through the excitation windings of each phase, and a magnetic field is generated between the stator 52 and the rotor 51.

The distribution circuit 72 connects the power transistors 6 to the excitation windings of each phase in accordance with the output pulses of the arithmetic circuit 74, as shown in a typical excitation sequence shown in FIG.
1 and 62 are configured to output a base signal that controls on/off.

In this example, 10 steps are repeated.

In this example, the storage circuit 73 stores specific speed fluctuations of the plurality of stepping motors 12 corresponding to a plurality of speeds of the optical system 3 to be driven, that is, a plurality of speeds corresponding to the reading magnification.

That is, in this motor drive circuit 36, the range up to the maximum operating speed is divided into multiple stages for each speed, and the speed fluctuations in the range of multiple steps (10 steps when the reading magnification is 100%) at each stage are calculated every 6 weeks. In advance, these speed fluctuation data are simulated into a sinusoidal fluctuation wave for one period taking into account the speed fluctuation amplitude, and this speed fluctuation data is stored in the storage circuit 73 in advance.

When the arithmetic circuit 74 receives a speed setting signal from the speed setter 75 (pulse generating means), it reads speed fluctuation data corresponding to the set speed from the storage circuit 73 (7, selected according to the set speed and the magnification). The interval (step interval) of the d-copulse supplied to the distribution circuit 72 based on the speed dust movement data
control. In addition, taking into consideration the phase of the speed fluctuation data read out from the memory circuit 73 at the time of 2', the above-mentioned method is set so that the fluctuation of the pulse rate defined by the reciprocal of the pulse time interval has almost the opposite phase with respect to the speed fluctuation. Controls the pulse interval. However, speed fluctuation data for an intermediate speed among the divided speeds is derived from speed fluctuation data before and after that speed.

The drive circuit 76 turns on and off the clutch 23 in accordance with the set speed of the speed setting signal supplied from the speed setter 75. That is, when the moving speed of the optical system 3 is low, the drive circuit 76
is turned on, and the mechanical damper 24 is connected to the stepping motor 12. As a result, the load moment of inertia of the optical system 3, that is, the stepping motor 12, increases, the driving of the optical system 3 becomes smoother, and the peak of high frequency components is drastically reduced. Further, when the moving speed of the optical system 3 is high, the clutch 23 is turned off by the drive circuit 76, and the mechanical damper 24 is separated from the stepping motor 12. As a result, the load moment of inertia of the optical system 3, that is, the stepping motor 12, can be reduced, and the rise characteristics are not adversely affected.

With such a configuration, when a certain speed is set by the speed setter 75, the output of the speed setter 75 increases at a constant slope to a level corresponding to the set speed. Speed setting device 7
When the output No. 5 rises, the calculation concave path 74 changes to the speed setting device 7.
The speed fluctuation data corresponding to the output of No. 5 is read out from the storage circuit 73, and the time interval of the output pulse is controlled based on the above output and the read speed fluctuation data. This variation in the pulse rate of the pulse interval is substantially in opposite phase to the speed variation data read out from the storage circuit 73. The output pulses of the arithmetic circuit 74 are given to the distribution circuit 72, and the distribution circuit 72 generates a base signal for turning on and off the power transistors 61 and 62 of the excitation circuit 71 in a predetermined order as shown in FIG. is output.

Therefore, the rotor 5 of the stepping motor 12 starts rotating.

In this case, since the excitation timing of each excitation phase A, B, and CSDSE is controlled taking into account the inherent speed fluctuations of the optical system 3, the inherent speed fluctuations can be canceled out and smooth rotation can be performed. can be set.

Further, when the output of the speed setter 75 rises, the drive circuit 76 turns on or off the clutch 23 in accordance with the set speed of the speed setting signal supplied from the speed setter 75. As a result, when the moving speed of the optical system 3 is low, the mechanical damper 24 is connected to the stepping motor 1.
2, and the optical system 3, that is, the stepping motor 12
The load moment of inertia increases, the driving of the optical system 3 becomes smoother, and the peak of high frequency components is drastically reduced. In addition, optical system 3
When the moving speed is high, the mechanical damper 24 is separated from the stepping motor 12, and the load moment of inertia of the optical system 3, that is, the stepping motor 12, can be reduced, and the rise characteristics are not adversely affected.

FIG. 9(a) shows excitation switching timing when the stepping motor 12 is driven to rotate at a constant speed. In accordance with this switching timing, the excitation of the excitation windings constituting each phase is switched. In this motor driving circuit 36, the time interval of excitation switching timing is set to Δt s with Δt as a reference.
It is varied between in and Δt Ilax. The reciprocal of this time interval is the pulse rate, and this pulse rate varies sinusoidally with a period T as shown in FIG. 9(b).

Normally, the optical system 3 always has unique speed fluctuations in each speed range. In this motor drive circuit 36, the period T is made to match the speed fluctuation period specific to the optical system 3, and the time interval of the excitation switching timing, that is, the pulse rate, is varied so that the period is almost in opposite phase. Therefore, assuming that the amplitude is set appropriately, the inherent speed fluctuation of the optical system 3 can be canceled out by the speed fluctuation accompanying the fluctuation of the pulse rate, and the rotor 51 can be rotated smoothly. can.

FIG. 10 shows an example in which the motor drive circuit 36 is used to reduce speed fluctuations of the hybrid type 5 ill stepping motor 12. This is because the pulse rate of the output pulse of the speed setting device 75 is 1500p as a driving condition.
ps, and the fluctuation frequency of the time interval of the excitation switching timing is set to 150 Hz, and the fluctuation phase is controlled so as to be in opposite phase to the inherent speed fluctuation of the optical system 3. The power spectrum at this time is the result shown in FIG. From this figure, it can be seen that the peak level at 1.50 Hz, which is the target for speed fluctuation reduction, has decreased dramatically and the speed waveform has become smooth.

In the embodiment described above, the speed fluctuation to be reduced corresponds to 10 steps, and the stepping motor 12 is capable of relatively smoothly changing the time interval of excitation switching timing.
This is an example targeting .

For example, in a two-phase stepping motor, the excitation phase is two
As a result, variations in the output torque due to variations in the excitation phase may correspond to four steps.

In such a case, even if an attempt is made to vary the time interval of the excitation switching timing in a sinusoidal manner, a smooth variation of force may not be obtained, and a sufficient speed variation reduction effect may not be obtained.

In this way, if a sufficiently smooth fluctuating force cannot be obtained, microstep driving may be used in combination. This driving method shifts the rotor stopping point by increasing/decreasing the voltage applied to different excitation windings that are simultaneously excited in stages, and the basic step amount can be varied from several steps to several dozen.
Can be divided into steps.

The concept of microstep drive will be briefly explained using FIG. 12. This example is a two-phase bibolar stepping motor, and the structure of the rotor 80 and stator 90 is almost the same as that of a five-phase stepping motor, but the number of excitation windings is two. The voltage applied to each excitation winding XSY is not in the form of a pulse, but in the form of a sine wave as shown in FIG. 13 by D/A converting the digital amount output from the digital arithmetic circuit. Further, the voltages applied to the excitation winding X1 and the excitation winding Y are made to have a phase shift of 90''.

When excited with such a driving method, the movement amount of the rotor becomes as shown in Fig. 13, and in this example, the basic step amount θ
Step operation is performed in steps of 1/4 of S.

In this way, when the speed fluctuation period is 4 basic steps, it is only necessary to periodically change the time interval of the excitation timing switching time in 16 steps, which makes it smoother and increases the speed fluctuation reduction effect. can be increased.

Although we have explained the case where microstep drive is used in conjunction with a 2-phase stepping motor, the same applies to 5-phase or 4-phase stepping motors, and the time interval of the excitation switching timing is periodically switched using microstep drive together. By doing so, the effect of reducing speed fluctuations can be increased.

Furthermore, if the present invention is a stepping motor, the shape,
It is not limited to the number of phases. In addition, although the above-mentioned embodiment describes application to the case where the speed fluctuation specific to the stepping motor has a single frequency component, even if it has multiple frequency components, the frequency is higher than the stepping motor drive frequency. The present invention can be applied within a small range.

As mentioned above, the effect of the mechanical damper can reduce the speed fluctuation of the moving scanning system, and at the same time, stepping at a pulse rate with an appropriate period that is the same period as the speed fluctuation of the moving scanning system and in the opposite phase. By driving the motor, speed fluctuations in the moving scanning system can be further reduced.

Furthermore, by separating the mechanical damper, it is possible to drive with less speed fluctuation even in areas where torque decreases.

If the frequency of speed fluctuations specific to the stepping motor is in a relatively high frequency range, microstep drive can be used in conjunction with the stepping motor to divide the basic step amount and make the time interval of excitation switching timing smoother. By varying the speed, speed fluctuations can be effectively reduced.

With this configuration, when a certain speed is set using the speed setting device 70, the mechanical damper and the stepping motor are connected and disconnected according to the set speed, and the load inertia moment is moved only in the area where the mechanical damper is effective. It can be added to the scanning system.

[Effects of the Invention] As described above, according to the present invention, even in the region where the torque of the stepping motor decreases, it is not affected by the load inertia of the mechanical damper, and the start-up characteristics deteriorate or step out occurs in the high-speed region. An image reading device that can prevent this can be provided.

[Brief explanation of drawings]

1 to 13 show an embodiment of the present invention, and FIG. 1 is a block diagram showing a schematic configuration of an image reading device;
FIG. 2 is a sectional view showing the configuration of the image reading device, FIG. 3 is a perspective view showing the internal structure of the image reading device, FIG. 4 is a vertical sectional view of the rotor in the stepping motor, and FIG. 5 is the rotor in the stepping motor. Figure 6 is a diagram showing the configuration of the stepping motor and motor drive circuit, Figure 7 is a diagram showing the configuration of the excitation circuit in the motor drive circuit, and Figure 8 is a diagram of the distribution circuit in the motor drive circuit. A diagram showing an operation sequence, FIG. 9(a) is a diagram showing an example of the pulse output of the arithmetic circuit in the motor drive circuit, and FIG. 9(b) is a diagram showing an example of converting the same pulse output into a pulse rate. Fig. 10 is a diagram showing the speed fluctuation results in an example in which the speed range during equal-magnification reading is controlled by a motor drive circuit, Fig. 11 is a diagram showing the power spectrum under the conditions shown in Fig. 10, and Figs. FIG. 13 is a diagram for explaining an example of the case where the microstep drive method is used together,
FIG. 14 is a diagram showing the relationship between the driving speed of the stepping motor and speed fluctuation, and FIG. 15 is a diagram showing the relationship between the driving speed and output torque of the stepping motor. 1...Main body, 3...Optical system, 4...Exposure lamp,
5, 6, 7...Mirror 9...Line sensor, ll
a...First carriage, 1lb...Second carriage, 12...Stepping motor, 23...Clutch (connection means), 24...Mechanical damper (external load element) 30...CPU, 36...Motor drive circuit, 51...Rotor, 52...Stator, 71...
Excitation circuit, 72... Distribution circuit, 73... Memory circuit,
74... Arithmetic circuit, 75... Speed setting device, 76...
・Drive circuit.

Claims (1)

[Scope of Claims] A reading means for reading an image; an instruction means for instructing a reading magnification of the image read by the reading means; and a scanning means for scanning the reading means at a speed corresponding to the reading magnification instructed by the instruction means. a scanning means, a stepping motor that drives the scanning means, an external load element that imparts a load moment of inertia to the stepping motor, and an external load element that applies a moment of inertia to the stepping motor; An image reading device comprising: connecting means for connecting an element to the stepping motor;