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# Calculation of Velocity Compensation Factors in Moving Head Printers

IP.com Disclosure Number: IPCOM000048451D
Original Publication Date: 1982-Feb-01
Included in the Prior Art Database: 2005-Feb-08
Document File: 3 page(s) / 44K

IBM

## Related People

Johnson, HW: AUTHOR

## Abstract

A simple technique is shown and described for providing on-the-fly determination of the correct lead distance over which to release ink drops so as to cause accurate placement of the drops on the paper by simultaneously measuring the head transport induced stream velocity, V(h), and quickly performing the calculation for the lead time d based on a measured value of drop flight time, T(f).

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Calculation of Velocity Compensation Factors in Moving Head Printers

A simple technique is shown and described for providing on-the-fly determination of the correct lead distance over which to release ink drops so as to cause accurate placement of the drops on the paper by simultaneously measuring the head transport induced stream velocity, V(h), and quickly performing the calculation for the lead time d based on a measured value of drop flight time, T(f).

The relation between velocity components V(h), V(s) and V(r) is shown in a previous article (*), along with a diagram which shows the relation between s, d, and r, where: v(h) equals head transport induced stream velocity v(s) equals pump pressure induced stream velocity

v(r) equals resultant drop velocity

d equals head displacement during drop flight or

horizontal component of drop displacement

during flight

s equals distance from drop break-off point to paper

r equals resultant drop displacement.

Since the corresponding angles of the triangles are equal, the triangles are similar and d divided by s equals v(h) divided by v(s) or d equals sv(h) divided by v(s) but s divided by v(s) is the drop flight time, T(f), and if a small tweak factor, k, is introduced to account for the aerodynamic and other neglected effects, d equals kv(h)T(f).

The significance of d is that it is the component of drop displacement during flight, which is parallel to the paper and thus represents the amount of "lead" required when releasing a drop in order to place it at a desired location on the paper.

The flight time, T(f), can be measured both statically and dynamically. The static measurement is taken with the head stationary and aligned with a flight time sensor.

During printing it is necessary to remeasure T(f) on a sufficiently frequent basis so as to follow its drift and to perform the above calculation for d as often as needed in order to compensate for changing v(h). This flight time measurement is taken with the head moving at nearly full speed, and thus is referred to as dynamic.

Since the flight time, T(f), is known from these measurements, this factor can be utilized to quickly perform the calculation for lead time d. This calculation can be performed by the block diagram circuitry shown in the drawing.

The locations on the paper at which drop placement is desired are called pel (picture element) addresses. The horizontal component

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of an address is obtained by signals generated by counting marks on an encoder scale as the head moves along, and is thus available as a digital word. It is then appropriate that d be similarly presented as a digital word so that algebraic manipulation of the address and the co...