EP2756956B1 - Method for the generation of a printed image on a rotating, three-dimensional body - Google Patents

Description

The present invention relates to a method for producing a printed image on a rotating, three-dimensional body having the features of the preamble of claim 1.

From the US 7,955,456 B2 is already the inkjet printing of blister packs known. These have a substantially two-dimensional to be printed sealing film and are conveyed linearly. Despite high production speeds printing is therefore easily possible. Far more difficult is the printing of three-dimensionally shaped bodies with curved outer surfaces in space, especially since these bodies must be rotated for printing in most cases.

However, it is also already known to use rotating, three-dimensional bodies, e.g. Bottles in bottling plants to print by means of an inkjet printing unit and it is also already been recognized the problem that the rotating body may have deviations from their desired position and thereby disturbances in the printed image to be generated can be called out.

The DE 10 2009 003 810 A1 For example, describes a system for printing on containers. It addresses the problem that the centering of the holder or the container is critical for printing at conventional 600 dpi and high conveying speeds. The solution to the problem is that the print head is automatically adjustable, using sensors that determine the location and angular position of the container and send these values to a controller. An adjustment of the timing for the inkjet printing unit is not described.

The DE 10 2009 014 663 A1 describes the non-contact (electro-optical or electromagnetic) determination of the rotational position of bottles by means of sensor unit and measuring marks. In paragraph 20 is explicitly described that the container longitudinal axis BA corresponds approximately to the axis of rotation DA: eccentrically rotating bottles are thus not recognized as a problem and accordingly offered no solution. An adaptation of the timing is not described.

However, bodies positioned eccentrically on a turntable constantly change their distance from a stationary printing unit, even at a constant angular speed of the turntable, whereby the surface portion of the body facing and facing the printing unit undergoes a constant change in web speed. This can lead to noticeable and therefore undesirable errors in the printed image to be generated as a result of changing printing resolution. Similar problems can occur when the body is centered on the turntable, but its outer surface in the section to be printed is not cylindrical or cylindrical section-shaped, or the angular velocity of the turntable changes. However, a direct measurement of the belt speed or its change is not possible with simple means.

Against this background, it is an object of the present invention to provide a comparison with the prior art improved method, which makes it possible to print rotating, three-dimensional body with a desired print resolution, even if the web speed of the printable and therefore a printing unit facing surface portion changes.

These objects are achieved by a method having the features of claim 1. Advantageous developments of the invention will become apparent from the accompanying dependent claims and from the description and the accompanying drawings.

An inventive method for producing a printed image on a rotating, three-dimensional body, wherein an ink jet printing unit with a plurality of ink jet nozzles arranged substantially on a straight line for printing with a pressure tact, the body rotates about a rotational axis substantially parallel to the straight line, and a motor for driving the rotation of the body is provided, and comprising the steps of: setting a fundamental frequency f ₀ (t) for driving the motor, driving the motor with the fundamental frequency f ₀ (t), and specifying a mean radius R _{0 of} the body, characterized by the further steps of: determining the radius change ΔR (t) of the body during rotating the body, calculating a correction value k (t) for a printing stroke of the printing unit, where k (t) = 1 + ΔR (t) / R ₀ , and driving the printing unit at a frequency f (t) for the printing clock, where f (t) = f ₀ (t) * k (t).

The method according to the invention advantageously makes it possible to use rotating, three-dimensional bodies, e.g. Bottles, or their (outer) surfaces or portions thereof having a desired printing resolution, e.g. with a constant dpi value, to print by the ink jet method even if the web speed of the surface portion to be printed and therefore facing an ink jet printing unit changes. According to the invention, its radius change at a preferably fixed measuring point is determined during the rotation of the body. This change in radius at the measuring point may occur e.g. from an eccentric positioning of the body, from its non-cylindrical shape or from a change in the angular velocity of the rotation of the body.

From the change in radius, a correction value is calculated according to the invention and the printing unit is driven with a frequency corrected relative to the fundamental frequency. Thus, the pressure cycle for the ink jet nozzles according to the invention is adapted to the radius change and the concomitant change in the web speed of the (outer) surface portion to be printed at the pressure point.

The measuring point and the pressure point are therefore preferably chosen so that they have at least one correlation. It may, for example, the measuring point in the direction of rotation of the body lie in front of the pressure point and the spatial distance converted into a time distance and taken into account in the control of the printing unit. The measuring point can also be substantially identical to the pressure point or be offset parallel to the axis of rotation (the latter preferably in the case of a non-changing in the direction of the axis of rotation of the body).

In this application, certain variables are given as a function of time t, for example f ₀ (t), .DELTA.R (t), k (t) and f (t). Alternatively, these variables may also be indicated as dependent on the angle α of the rotation, where α = ω (t) · t, where ω (t) is the angular velocity of the rotation. At constant angular velocity ω ₀ , it is sufficient to specify the variables for the values α = 0 to 360 ° or even in a narrower angular range, if only in this is to be printed.

The determination of the radius change preferably takes place substantially immediately prior to the printing. However, according to an alternative, it may also be provided that the determination of the radius change has already been made for a period of time, e.g. a few seconds or minutes, before printing and store the result in a cam and use this when printing for the frequency correction. If the problem of radius change is essentially caused solely by the (outer) shape of the body, its shape or radius change during a complete rotation can also be permanently stored and retrieved whenever such bodies are printed.

A preferred development of the method according to the invention can be distinguished by the fact that the determination of the radius change ΔR (t) takes place as non-contact measuring with a rangefinder, in particular with a triangulation measuring device. Compared with non-contact rangefinders or sensors there is the advantage that no disturbing influences on the surface to be printed or already printed, for example, by deformation or abrasion, and thus errors in the printed image can be advantageously avoided. Triangulation measuring devices or sensors also have the advantage that essentially all materials can be detected and that these allow very fast measurements. Alternatively, it can also be provided to use capacitive or inductive working distance sensors.

A further preferred development of the method according to the invention can be distinguished in that the distance meter measures the distance D (t) between the inkjet nozzles and the surface of the body at the point at which the ink drops are to hit the surface, where ΔR (t ) = D (t) _M - D (t), with D (t) _M as the time average of D (t). In particular, when using a triangulation meter, this approach is advantageous because the device allows the distance to the surface, so the distance D (t) to measure directly. From this distance lets calculate the radius change.

A further preferred development of the method according to the invention can be distinguished by the fact that for the time average D (t) _M = D ₀ -R ₀ , with D ₀ as the distance between the inkjet nozzles and the axis of rotation. So if D ₀ and R _{0 are} known, the determination of D (t) and thus of ΔR (t) is very simple, for example, when printing bottles with a constant radius R ₀ in the surface to be printed and positioning these bottles on a Turntable with rotation axis at a constant distance D ₀ to the inkjet nozzles.

A further preferred development of the method according to the invention can be characterized in that the specification of a mean radius R _{0 of} the body is based on the determination of R ₀ = D ₀ -D (t) _M , with D ₀ as the distance between the inkjet nozzles and the axis of rotation and with D (t) _M as the time average of D (t). Thus, for example, if the body has an irregular (outer) shape, in contrast, for example, to a bottle of known and constant R ₀ , can advantageously by averaging over a period corresponding to a rotation of 360 ° (or less, if only one peripheral section is to be printed), R ₀ are calculated according to the given formula.

A further preferred development of the method according to the invention can be characterized by the further step of: setting an angular velocity ω (t) of the rotation of the body, wherein for the fundamental frequency f ₀ (t) = ω (t) · R ₀ / a valid with a as a resolution of the printed image. Due to the proportionality between the Angular velocity and the fundamental frequency, the latter can be easily calculated with knowledge of the resolution to be achieved during printing (eg as the smallest desired distance of the pressure points in the circumferential direction).

A further preferred embodiment of the method according to the invention can be characterized in that the angular velocity is a constant ω ₀ and thus also the fundamental frequency is a constant fo, where fo = ω ₀ · R ₀ / a.

A further preferred development of the method according to the invention can be distinguished by the fact that the calculation of the correction value k (t) takes place substantially continuously. It can e.g. be provided to determine the radius change continuously, at least continuously during a complete revolution of the body (or less, if only a peripheral portion to be printed) and from the value for ΔR (t) the value of k (t) and from there the value of f (t) to calculate for the control. If the measuring point substantially coincides with the pressure point or the time offset .DELTA.t between measuring and printing is known, a real-time correction of the control frequency f (t) can advantageously take place with the use of fast computers and data connections, possibly with a time offset of .DELTA.t ,

In the context of the invention, a device for carrying out the above-mentioned inventive method and its developments is to be seen. Such a device has the components necessary for carrying out the method steps according to the invention: an inkjet printing unit with control, a motor with control, a rangefinder and a computer for the calculations of the correction value.

The described invention and the described, advantageous developments of the invention are also in combination with each other advantageous developments of the invention.

The invention as such and structurally and / or functionally advantageous developments of the invention will be described below with reference to the accompanying drawings with reference to a preferred embodiment.

Fig. 1

Eine schematische Darstellung eines bevorzugten Ausführungsbeispiels des erfindungsgemäßen Verfahrens anhand der Abläufe beim Betrieb einer Vorrichtung zum Bedrucken von rotierenden Körpern.

The drawing shows:

Fig. 1

A schematic representation of a preferred embodiment of the method according to the invention with reference to the procedures during operation of a device for printing of rotating bodies.

FIG. 1 shows a device 1 for printing, ie for generating a printed image of rotating, three-dimensional bodies 2. By way of example, a bottle to be printed is shown, wherein not the complete surface 3 of the bottle, but only a section 4, for example a label or a band, to be printed. The bottle is essentially rotationally symmetrical, but it is not centered on a turntable 5, that is, its axis of symmetry does not coincide with the axis of rotation A of the turntable. Due to the (usually unwanted) eccentric recording on the turntable occurs during the rotation of the turntable and thus the body at a time t changing distance D (t) between the surface of the body and an ink jet printing unit 6 and their ink jet nozzles 7 arranged substantially on a straight line G and at a time-varying radius R (t). R (t) is determined as the distance of the surface of the body facing the ink-jet printing unit (the location of the surface at which the ink drops 8 are to hit the surface) to the axis of rotation. The axis of rotation is aligned substantially parallel to the straight line G. D ₀ is the substantially constant distance between the ink jet nozzles and the axis of rotation and R ₀ the mean radius of the body, in the example, the substantially constant radius of the bottle, designated. ΔR (t) denotes the change in radius between the surface of the body facing the ink-jet printing unit and the surface of an imaginary center 2 'received on the turntable, directed toward the ink-jet printing unit. The distance between the surface of the imaginary body facing the ink-jet printing unit and the Ink jet printing unit is denoted by D (t) _M. D (t) _M can also be understood as a time average of the distance D (t) changing with time t.

The device 1 further comprises a rangefinder 8, in particular a triangulation measuring device, with which the determination of the radius change ΔR (t) takes place as non-contact measuring. The rangefinder first measures the value of D (t). From this value and its mean value D (t) _M , ΔR (t) can be calculated according to the formula ΔR (t) = D (t) _M -D (t). This calculation can be carried out in a control unit 10, to which the measurement result D (t) is made available. In the simple case of the example of the bottle of constant and known radius R ₀ , D (t) _M can simply be determined according to the formula D (t) _M = D ₀ -R ₀ , from which ΔR (t) = D ₀ -R ₀ - D (t) yields. On the other hand, presetting the mean radius R _{0 of} the body (eg, if this body is non-rotationally symmetric, flattened, or irregularly shaped) may be based on determining R ₀ = D ₀ -D (t) _M.

Further shows FIG. 1 a motor 11 for driving the rotation of the body 2, that is, in the example shown, for rotationally driving the turntable 5. The motor is driven at a predetermined fundamental frequency f ₀ (t). For example, an angular velocity co (t) of the rotation of the body may be predetermined by the control unit 10 and provided to and from the motor 12, and for the fundamental frequency f ₀ (t) = ω (t) * R ₀ / a , with a as the resolution of the printed image. If the predetermined angular velocity is a constant ω ₀ , the fundamental frequency is also a constant fo, where fo = ω ₀ · R ₀ / a. In the simple case, a rotationally symmetrical body is for example 2 with kontantem radius R ₀ ω rotated at a constant angular speed _0, wherein the body rotates eccentrically.

The ink jet nozzles 7 require a printing stroke f (t) for printing, with which the ink droplets are ejected. This pressure cycle is generated by the control unit 10 as a frequency and transmitted to a pressure control unit 13 and from this to the pressure unit 6. The control of the pressure unit with a frequency f (t) for the pressure cycle takes place according to the invention according to the formula f (t) = f ₀ (t) · k (t), where k (t) is a correction value with respect to the frequency with which the motor 11 is controlled is. Calculating this Correction value k (t) for the pressure cycle of the pressure unit takes place according to the invention according to the formula k (t) = 1 + ΔR (t) / R ₀ . The following example clarifies the underlying principle: If the body 2 of the printing unit 6 comes closer with its surface 3, eg because of its eccentric positioning, during the rotation, the web speed of the surface increases at the point where the ink drops 8 are to strike because these points now have a greater distance (radius R (t)) to the axis of rotation A. Therefore, to maintain a given resolution a, the ink drops must be ejected at a higher frequency. If the surface is removed, the web speed decreases and the frequency must be lowered accordingly.

The calculation of the correction value k (t) preferably takes place essentially continuously. For this purpose, the distance D (t) is measured continuously (or quasi-continuously or clocked with a clock frequency on the order of the printing frequency or higher) with the rangefinder 9 and this value in the control unit 10 for calculating the correction value k (t) and for the Control of the printing unit 9 with the pressure clock f (t) = f ₀ (t) · k (t) used.

LIST OF REFERENCE NUMBERS

1

contraption

2

body

2 '

imaginary body

3

surface

4

section

5

turntable

6

Inkjet printing unit

7

inkjet nozzles

8th

ink drops

9

rangefinder

10

control unit

11

engine

12

Engine control unit

13

Pressure control unit

A

axis of rotation

G

Just

D (t)

distance

D (t) _M

average distance

D ₀

distance

R (t)

radius

.DELTA.R (t)

radius change

R ₀

average radius

Claims (8)

1. Method for creating a printed image on a rotating, three-dimensional body, the method wherein an inkjet printing unit (6) having a plurality of inkjet nozzles disposed substantially along a straight line (6) for printing at a printing clock rate is provided, the body is rotated about an axis of rotation (A) substantially parallel to the straight line (G), and a motor (11) is provided to drive the rotation of the body, comprising the steps of
   prescribing a fundamental frequency f₀(t) for activation of the motor (11), activating the motor (11) with the fundamental frequency f₀(t) and
   prescribing an average radius R0 of the body (2),
   characterized by the further steps of
   determining the change in radius ΔR(t) of the body (2) during rotation of the body (2)
   calculating a correction value k(t) for a printing clock rate of the printing unit (6) where k(t) = 1 + ΔR(t) / R₀, and
   activating the printing unit (t) with a frequency f(t) for the printing clock rate, where $$\mathrm{f}\left(\mathrm{t}\right)={\mathrm{f}}_{\mathrm{0}}\left(\mathrm{t}\right)\times \mathrm{k}\left(\mathrm{t}\right)\mathrm{.}$$

   
2. Method according to claim 1
   characterized in
   that the step of determining the change in radius ΔR(t) is a contactless measurement by means of a distance meter (9), in particular a triangulation measuring device.
3. Method according to claim 2,
   characterized in
   that with the distance meter (9), a distance D(t) between the inkjet nozzles (7) and the surface (3) of the body (2) is measured at a point at which the drops of ink are intended to impinge on the surface, where ΔR(t) = D(t)_M - D(t) and D(t)_M is an average value over time of D(t).
4. Method according to claim 3,
   characterized in
   that D(t)_M = D₀ - R₀ applies for the average value over time, where D₀ is a distance between the inkjet nozzles (7) and the axis of rotation (A).
5. Method according to any one of the preceding claims,
   characterized in
   that the step of prescribing the average radius R₀ of the body (2) is based on a determination of R₀ = D₀ - D(t)_M, where D₀ is a distance between the inkjet nozzles (7) and the axis of rotation (A) and D(t)_M is an average value over time of D(t).
6. Method according to any one of the preceding claims,
   characterized by
   the further step of prescribing an angular velocity ω(t) of the rotation of the body (2), where f₀(t) = ω(t) × R0 / a applies for the fundamental frequency and a is a resolution of the printed image.
7. Method according to claim 6,
   characterized in
   that the angular velocity is a constant ω₀, and consequently the fundamental frequency f₀ is also a constant, where f₀ = ω₀ × R₀/a.
8. Method according to any one of the preceding claims,
   characterized in
   that the step of calculating the correction value k(t) is carried out substantially continuously.

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