Geometrical instruments – Gauge – With support for gauged article
Reexamination Certificate
2001-11-04
2003-10-07
Gutierrez, Diego (Department: 2859)
Geometrical instruments
Gauge
With support for gauged article
C033S702000, C358S406000, C358S474000
Reexamination Certificate
active
06629374
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method and an apparatus for linearity measurement in a reproduction appliance that contains an operating carriage bearing a scanning or recording device and that can be moved in discrete steps along a straight line.
Reproduction appliances that contain an operating carriage having a scanning or recording device are, for example, scanners, engraving machines, or exposers for printing plates, films, foils, paper, and so on. The drive to the operating carriage is generally provided through force transmission elements that are connected by a form fit, for example, spindles, racks, toothed belts, and/or gear wheels. Such force transmission elements have production-induced errors, which can impair the linearity of the advance travel, so that they have to be taken into account in the high resolution demanded of reproduction appliances.
For instance, in the case of exposers, a linearity of less than 0.01% (1×10
−4
) is required for both directions of the exposure. Thus, for a distance of one (1) meter, the linearity deviation must not be more than +/−50 &mgr;m. To achieve such accuracy in the advance direction of the operating carriage, one needs highly precise force transmission elements such as transport spindles, which operate on the circulating ball principle and have a pitch error of less than 1 &mgr;m per revolution. Such drive elements, such as those for the transmission of forces in precision machine tools, are very costly. In addition, they are over dimensioned for the use in reproduction appliances because the forces to be transmitted in reproduction appliances are relatively small. For the low-torque drive motors in exposers, they even have, with their configuration-induced torque fluctuations, considerable disadvantages.
In the case of reproduction appliances, it would intrinsically be possible to use simpler and, therefore, less accurate drive elements if the linearity error were measured and the drive to the reproduction appliances were corrected appropriately during operation. Methods of length measurement that supply the necessary accuracy are, for example, registering measured values by interferometers or glass scales. However, their resolution would have to be chosen to be significantly higher than the demanded measurement accuracy because these methods have superimposed systematic errors that exceed the theoretically achievable resolution many times over. In addition, such high-resolution length measurement systems are extremely complicated in terms of manufacture and application.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method and apparatus for linearity measurement that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type such that a simple and cost-effective linearity measurement is made possible in a reproduction appliance.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a method for linearity measurement in a reproduction appliance, including the steps of providing an operating carriage bearing at least one of a scanning device and a recording device, successively moving the operating carriage along partial segments of a straight line in discrete steps in a given direction along the straight line, each of the partial segments being longer than a travel corresponding to one of the steps and being shorter than the entire length of the line, the partial segments each having an exactly defined length defined by an additional carriage moveable along the given direction, counting a number of steps needed for each partial segment, and calculating deviations between values for a travel of the operating carriage resulting from the partial segment and values for the travel of the operating carriage resulting from counting the steps.
In that the necessary devices are integrated into the reproduction appliance, or are already present therein, the method can be carried out completely within the machine. Alternatively, a suitable measuring tool can be inserted into the machine and, after the recording and storage of the data, is removed again. The evaluation of the data can be carried out either in the reproduction appliance or outside it, for example, on a personal computer.
The counting of the discrete steps is available in any case in a reproduction appliance that has an incremental drive for the operating carriage, for example, a stepping motor, so that the internal machine measuring increments can additionally be used to carry out the method according to the invention. Otherwise, the counter values can be easily obtained electronically, for example, by an incremental encoder that is connected to the drive. It is, therefore, possible for internal machine measuring increments that are already present, such as the steps from a stepping motor or rotary encoder cycles, to be used additionally to carry out the method.
The only mechanical parts that have to be fabricated and adjusted precisely are the additional carriage and its drive. However, these precision requirements can be fulfilled without great expenditure because the length defined with the aid of the additional carriage is substantially shorter than the entire travel of the operating carriage.
In accordance with another mode of the invention, at the start the operating carriage is moved to the start of the line, and the additional carriage is moved into a first relative position between the operating carriage and the additional carriage. The additional carriage is then moved into a second relative position between the operating carriage and the additional carriage, the distance between the first and the second relative position corresponding to the length of a partial segment, also referred to as a part line. Next, the operating carriage is shifted forward while the discrete steps are counted and while the additional carriage remains in place. The operating carriage is stopped as soon as the first relative position between the operating carriage and the additional carriage has been reproduced. The additional carriage is then moved again into the second relative position while the operating carriage remains in place, and the alternating forward shifting of operating carriage and additional carriage is repeated until the entire line has been measured.
In accordance with a further mode of the invention, the part lines that are traveled over successively preferably all have the same length. As a result, both the definition of the precisely defined lengths and the evaluation of the measured results are made easier. Specifically, in accordance with added modes of the invention, the two relative positions between the operating carriage and the additional carriage can be defined or produced in a very simple way such as with mechanical stops, electromechanical drives, and/or optical sensors. The first relative position can be defined, for example, with the aid of a stop, while an optical device such as a differential light sensor are rather more suitable for defining the second relative position.
In accordance with an additional mode of the invention, the additional carriage is moved into the first relative position with an electromechanical device before traveling over each partial segment. The electromechanical device moves the additional carriage into the first relative position before traveling over each partial segment, the electromechanical device being connected to the additional carriage.
In accordance with yet another feature of the invention, the additional carriage is held in the first relative position with one of a self-locking device and self-retaining device while the operating carriage is shifted forward.
The additional carriage preferably has a self-locking device in order to remain in the first relative position when the operating carriage is shifted forward. Alternatively, an active brake or other blocking device can be provided for the additional car
Haushahn Volker
Melzer Peter
Wirtz André
Greenberg Laurence A.
Gutierrez Diego
Heidelberger Druckmaschinen AG
Mayback Gregory L.
Smith R. Alexander
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