Facsimile and static presentation processing – Static presentation processing – Position or velocity determined
Reexamination Certificate
2001-02-05
2002-02-12
Evans, Arthur G. (Department: 2622)
Facsimile and static presentation processing
Static presentation processing
Position or velocity determined
C358S001100
Reexamination Certificate
active
06346992
ABSTRACT:
BACKGROUND OF THE INVENTION
1. FIELD OF THE INVENTION
The invention relates to a drive system for a carriage, which is fitted with a scanning or recording device, in a reproduction appliance. In the reproduction appliance, the scanning or recording device scans an original or exposes a recording material periodically along scanning or recording lines. The carriage is moved forward with the aid of a drive apparatus along a straight line at right angles to the scanning or recording lines. The drive apparatus contains an electric motor whose rotation speed is determined by a frequency of drive pulses which are produced by dividing a master clock by an integer factor, and contains an apparatus for converting the rotary movement of the electric motor into a linear movement of the carriage.
One example of such a reproduction appliance is a so-called internal drum recorder or exposure unit for recording information on a recording material which is lying on the inside of a cylindrical trough. The recording is often made by a focused light beam that is aimed at the recording material from a rotating deflection device that is disposed on the imaginary axis of the cylindrical trough. While the deflection device is rotating quickly, it is moved in steps or continuously along the axis, so that the recording material is exposed along helical or circular lines, predominantly with raster-image motifs.
Another example of a reproduction appliance is an external drum scanner for optical scanning of an original which is disposed on the outside of a cylindrical drum, in order to digitize image information located on the original. In this example, the drum normally rotates, while an optoelectric scanning device is moved slowly parallel to the drum axis.
In reproduction appliances such as this, the carriage which is fitted with the scanning or recording device and is moved axially is driven, for example, by an axially running threaded spindle which is rotated by an electric motor, which is frequently a stepping motor. Other drives operate, for example, with a steel strip or a cable, or a linear motor is used. The frequency of the drive pulses for the stepping motor must be finely adjustable and must be kept very constant during the scanning or recording process since even very small position errors can adversely affect the recording or scanning quality.
Conventionally, the drive pulses are obtained from a high-frequency master clock which is divided in a divider by an integer factor which is chosen such that the speed of the resultant feed movement is as close as possible to a desired feed rate. In order to allow the frequency of the drive pulses to be adjusted finely, it is either necessary to use very high master clock frequencies in the Gigahertz band, which can be processed only by using logic circuits based on ECL technology, or synthesizers are required, with analog phase lock loop (PLL) chips which can divide both the integer and fractional parts.
These techniques require a relatively high level of complexity and, furthermore, are associated with problems. With Gigahertz technology, it is difficult to develop electromagnetically compatible circuits, and with synthesizers jitter and drift phenomena can easily occur, which must in turn be compensated for with a great deal of complexity in order to achieve the necessary frequency stability.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a drive system for a scanning device or a recording device for a reproduction appliance which overcomes the above-mentioned disadvantages of the prior art devices of this general type, which, using comparatively simple devices, can produce a feed movement whose speed can be adjusted finely and can be kept highly constant.
With the foregoing and other objects in view there is provided, in accordance with the invention, a drive system for a carriage fitted with an apparatus being a scanning apparatus or a recording apparatus. The carriage is disposed in a reproduction appliance, and the apparatus performs one of scanning an original and exposing a recording material periodically along one of scanning lines and recording lines. The drive system contains a drive apparatus for moving the carriage forward along a straight line at right angles to one of the scanning lines and the recording lines. The drive apparatus includes an electric motor having a rotation speed determined by a frequency of drive pulses produced by dividing a master clock by an integer factor; an apparatus for converting a rotary movement of the electric motor into a linear movement of the carriage; and a device by which a duration of an identical number of the drive pulses can be changed by at least one period of the master clock in each operating period of the apparatus.
For a drive system according to the invention, the object is achieved by a device with which the number of drive pulses can be lengthened or shortened by one or more periods of the master clock in each scanning or recording period.
The technique of lengthening individual pulses, which have been obtained by integer subdivision from a master clock, by one or more periods of the master clock in order to adjust the frequency of the pulses very much more finely than the frequency interval between integer fractions of the master clock is known per se as “clock stealing” or a “binary fraction divider” technique. The invention also covers the action on the periodic master clock being synchronized to the scanning or recording period. This measure prevents the creation of interference frequencies in the drive pulses, which can lead to beating with machine frequencies or with the raster frequency which may, in turn, lead to visible and thus disturbing strip or Moire patterns.
According to the invention, the mean speed of the feed movement of the carriage at right angles to the scanning or recording lines can be adjusted very finely, even if the frequency of the master clock is not as high as would be necessary without “clock stealing”. Specifically, in addition to the integer factor that is used for dividing the master clock, two further factors are available which can be varied in order to set the desired feed rate. These factors are the number of drive pulses in each scanning or recording period which are in each case lengthened or shortened by one or more periods of the master clock, and the number of periods of the master clock by which the respective drive pulses are lengthened or shortened in each scanning or recording period. Master clock frequencies of less than approximately 100 MHz are thus sufficient for practical applications. These are frequencies that can be produced and processed without any problems using simple digital techniques such as TTL technology.
The frequency of the master clock itself can always be kept constant for the invention since even the process of accelerating the electric motor at the start of a scanning or recording process can be controlled by suitably varying the factors which govern the feed rate. A constant-frequency master clock can be produced and kept constant considerably more easily than a variable frequency master clock, as has been required until now.
The synchronization of the lengthening or, alternatively, shortening of individual drive pulses with the scanning or recording period is achieved in that the feed distance from one scanning or recording line to the next is always the same. There are thus no density fluctuations in a scanned or recorded raster pattern, which can lead to visible strip or Moire patterns.
According to the basic solution of the invention, individual drive pulses in each scanning or recording period can either be lengthened or shortened. The first of these alternatives is preferable for practical implementation of the invention by commercially available electronic components. Specifically, in an embodiment such as this, individual drive pulses in each scanning or recording period are lengthened by one or more periods of the master clock by masking out the same number of periods of the m
Haushahn Volker
Melzer Peter
Evans Arthur G.
Greenberg Laurence A.
Heidelberger Druckmaschinen AG
Lerner Herbert L.
Stemer Werner H.
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