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Variable Compensation for Acceleration in Hand Scanned Codes

IP.com Disclosure Number: IPCOM000087165D
Original Publication Date: 1976-Dec-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 5 page(s) / 49K

Publishing Venue

IBM

Related People

Larsen, LD: AUTHOR

Abstract

A rectangular waveform recorded upon some medium (optical or magnetic bars, for example) may be represented as shown in Fig. 1. The information in such a waveform resides in the relative distances between transitions (or edges). If such a spatial waveform is scanned with a device responsive to the transitions, then a time-varying waveform will result. This waveform will contain distortions reflecting the spatial inaccuracies contained in the recorded waveform plus the additional distortions introduced by the scanning process itself.

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Variable Compensation for Acceleration in Hand Scanned Codes

A rectangular waveform recorded upon some medium (optical or magnetic bars, for example) may be represented as shown in Fig. 1. The information in such a waveform resides in the relative distances between transitions (or edges). If such a spatial waveform is scanned with a device responsive to the transitions, then a time-varying waveform will result. This waveform will contain distortions reflecting the spatial inaccuracies contained in the recorded waveform plus the additional distortions introduced by the scanning process itself.

A major source of distortion introduced by the scanning process may be the variation of velocity (acceleration) which occurs during the scan. This article is concerned with a technique for compensating for the accelerations characteristically produced by human operators using a hand-held scanning device.

When a rectangular recorded waveform is scanned, the velocity variation of the sensor will cause a distortion of the resulting time waveform. Thus the success of an attempt to predict the next possible like transition time will depend upon the change in velocity in the region of interest. This change in velocity may be predicted if something is known about the behavior of velocity over past interval(s) of time or distance. For example, if the average velocity over the last interval is known, a prediction may be made that that velocity will remain constant over the next interval. This most basic first order compensation may be expressed as (V(n))(p) = V(n-1), where (V(n))(p) is the predicted average velocity (unit widths per unit time) over the 'next' interval and V(n-1) is the measured average velocity over the last interval.

Actually, it is somewhat easier to work with the inverse of the velocity or time per unit width. Thus if (T(n))(p) = 1/(V(n))(p) and T(n-1) = 1/V(n-1), then (T(n))(p)= T(n-1) describes the first order compensation. If the time to traverse a unit width in the nth interval is predicted to be (T(n))(p), and the distance to the next like transition is known to be 2, 3 or 4 unit widths because of the form of distance coding used, then the predicted elapsed time to the next like transition, (t(n))(p), will be 2(T(n))(p)3(T(n))(p) or 4(T(n))(p).

A more elaborate compensation may be devised if a prediction is made based upon the performance over two past intervals. In general, this may be described as follows: (T(n))(p) = T(n-1). f(T(n-1),Tn-2). For example, if f(T(n-1), T(n-2) = T(n-1/T(n-2), then (T(n))(p) = T(n-1)2/T(n-2). This function presumes that for the nth interval, the predicted time per unit, (T(n))(p), will be T(n-1) times the ratio of T(n-1)/T(n-2). If T(n-1)/T(n-2) < 1, velocity is perceived to be increasing and so (T(n)(p) will be made smaller than T(n-1); the converse is true for T(n-1)/T(n-2) > 1.

Of course, it is possible to use more than two previous intervals to predict the velocity over the next interval; ho...