Patent Description:
Sheet processing machines, also known as converting machines, are used in the packaging industry for processing raw materials, e.g. cardboard, paper or foils, into intermediate or finished products, typically in the form of sheets. Converting operations can e.g. include printing, cutting, creasing, blanking, stamping and/or folding-gluing. Typically, the individual operations are done in subsequent processing stations of the sheet processing machine with the sheets being conveyed from one processing station to the subsequent one by a transfer mechanism.

The processed sheets can be collected in a sheet pile, i.e. in a vertical stack of sheets, after processing in a designated receiving area of the sheet processing machine. It is desirable to collect a defined batch size of processed sheets in the receiving area to simplify subsequent handling and/or logistic steps.

As the sheets have a defined thickness, the batch size corresponds to the height of the sheet pile. To measure the height of sheet piles, sheet processing machines as known in the art, for example in <CIT>, can comprise a light barrier arranged at a pre-determined height of the receiving area.

However, the size and shape of the processed sheets, e.g. of blanks pushed out of the sheets, vary between different sheet processing jobs. Therefore, the position of the components of the light barrier, i.e. of a light emitting element and of a light receiving element, must be carefully adjusted by a skilled operator of the sheet processing machine. This adjustment process is time-consuming and typically necessitates many complex handling operations, e.g. opening the corresponding processing station of the sheet processing machine, handling safety mechanisms for the operator, removing tools used in the processing stations etc..

More complicated detection systems which would not need any additional adjustment for different sheet processing jobs, e.g. a light curtain comprising a multitude of light barriers and monitoring the complete receiving area, are too expensive for most applications.

The object of the invention is to provide a simple and cheap means for measuring a height of a sheet pile, especially a means suited to measuring the height of the sheet pile for sheets of differing shape and/or size.

<CIT> discloses a system to control the height of a sheet pile using a light beam. The system is used in a drawer containing binder sheet (that help containing a pile of blanks). The light beam position being fixed, and the pile is lifted up until it cuts the beam. <CIT> uses a similar system applied to the pile of sheets at the input of a printer.

The object of the invention is solved by a sheet processing machine comprising a receiving area for collecting a sheet pile and a device for determining the height of the sheet pile. The device comprises a manually displaceable first sensor element arranged at a first side of the receiving area, and an automatically displaceable second sensor element arranged at an opposite side of the receiving area such that the first and second sensor elements are arranged opposite each other along a width direction of the receiving area. The first sensor element and the second sensor element are displaceable along a length direction of the sheet receiving area, wherein the first sensor element is one of a light emitting source and a light receiving sensor and the second sensor element is the other one of a light emitting source and a light receiving sensor. The light emitting source and the light receiving sensor form a light barrier along the width direction when facing each other.

The invention is based on the idea to combine a first sensor element manually handled by the operator with a second sensor element which is adapted to automatically adapt its position relative to the first sensor element, i.e. the position of the second sensor element does not need to be manually adjusted by the operator, too. This eliminates the need of carefully adjusting the first and second sensor element manually by the operator and allows less well-trained personnel to operate the sheet processing machine.

Further, the sheet processing machine according to the invention does not require complex handling operations for setting up the device for determining the height of the sheet pile. Therefore, downtimes of the sheet processing machine between different sheet processing jobs can be reduced.

At the same time, by keeping a manually adjustable sensor element, the operator can adapt the position of the light barrier to be suitable for the size and/or shape of the sheets obtained in the receiving area for the sheet processing job at hand.

Further, the device for determining the height of the sheet pile is simple and cheap, as a single light barrier is sufficient for reliably determining if the sheet pile has reached the height at which the light barrier is present.

To keep the device for determining the height of the sheet pile as cheap and simple as possible, preferably only one light emitting element and only one light receiving sensor is used.

The width direction and the length direction are especially perpendicular to each other.

The first sensor element and the second sensor element can be mounted on a first rail and a second rail, respectively. The first rail and the second rail are especially parallel to each other.

To simplify the construction of the device for determining the height of the sheet pile, the first rail and the second rail can be linear rails.

In one variant, the first sensor element is mounted by a slotted guide slider in a slotted guide of the first rail. The slotted guide slider especially extends out of the slotted guide such to be manageable by the operator of the sheet processing machine. Accordingly, the position of the first sensor element can be adjusted by the operator by moving the slotted guide slider in the slotted guide to the desired position.

The second sensor element can be displaceable by means of a motor of the second sensor element, especially an actuator of the second sensor element. The motor can be connected to the second rail and enables the device for measuring the height of the sheet pile to adjust the position of the second sensor element in an automated manner.

Preferably, the device comprises a control unit connected to the first sensor element and to the second sensor element, the control unit being adapted to receive a sensor signal from the light receiving sensor and to control the movement of the second sensor element. Accordingly, the control unit is responsible for ensuring that the first and second sensor element face each other so that the light barrier is formed.

The control unit is especially adapted to move the second sensor element along the length direction to a working position, wherein in the working position the sensor signal is non-zero. Preferably, the sensor signal is maximum when the second sensor element is in the working position.

A "non-zero" sensor signal here and in the following means that the sensor signal is above the noise level of the corresponding light receiving sensor.

As long as the first and second sensor elements, and therefore the light emitting source and the light receiving sensor, are not facing each other, the light barrier cannot be successfully formed, i.e. the light emitted by the light emitting source cannot reach the light receiving sensor. When the alignment is optimal, the sensor signal is expected to be maximum. This allows the control unit to use the sensor signal received from the light receiving sensor as control variable when searching for the correct position of the second sensor element, i.e. for the working position of the second sensor element.

For this purpose, the control unit can be adapted to move the second sensor element along the whole length of the second rail and afterwards move the second sensor element to the position associated to the maximum sensor signal.

Alternatively, the control unit can be adapted to stop the movement of the second sensor element along the second rail as soon as the sensor signal decreases by a pre-determined first threshold value after increasing by a pre-determined second threshold and to move the second sensor element back to the position before the sensor signal started to decrease. With other words, the control unit can be adapted to stop the movement of the second sensor signal after the first time a maximum of the sensor signal has been identified. As preferably only a single light emitting source is used, there is no need to continue measuring the sensor signal for all further positions of the second sensor element along the second rail.

The first and second threshold need to be chosen such that random fluctuations in the sensor signal, e.g. due to noise, are not erroneously indicating a maximum value of the sensor signal. , the first and second threshold can be determined as a multiple of the noise level of the light receiving sensor, e.g. ten times the noise level. Of course, the first and second threshold can have the same or different values.

Further, the control unit can be adapted to move the second sensor element to the working position each time the first sensor element has been moved. In this way, it can be ensured that each time after the operator manually re-adjusts the position of the first sensor element to be in line with a new sheet processing job, the second sensor element automatically becomes aligned to form the light barrier.

In addition, the control unit can be configured to only move the second sensor element to the working position after the first sensor element has been moved a distance corresponding to a displacement threshold. This ensures that the control unit does not re-adjust the position of the second sensor element after minimal movements of the first sensor element, e.g. due to vibrations of the sheet processing machine.

Additionally, the control unit can be adapted to move the second sensor element only when the sheet processing machine is in a set-up mode.

The set-up mode can be started and ended by the operator by means of a human-machine-interface. The human-machine-interface especially can be used for controlling the sheet processing machine and to display information about the current state of the sheet processing machine.

Preferably, the first sensor element is arranged at an operator side of the sheet processing machine and the second sensor element is arranged at an opposite operator side of the sheet processing machine. Accordingly, the operator of the sheet processing machine can easily access the first sensor element which needs to be handled manually while the second sensor element, which is laborious and time-consuming for the operator to access, can be handled automatically.

The receiving area can be part of a blank separation station of the sheet processing machine and the sheet pile can be a pile of blanks. Blanks produced by processing sheets can have a wide variety of sizes and/or shapes such that it is especially advantageous to use the device for determining the height of the sheet pile which is adjustable to the blanks produced in the present sheet processing job.

Further advantages and features will become apparent from the following description of the invention and from the appended figures which show a non-limiting exemplary embodiment of the invention and in which:.

<FIG> schematically shows a sheet processing machine <NUM> making it possible to cut blanks <NUM> from a succession of sheets <NUM>. These blanks <NUM> are usually intended to be subsequently folded and bonded to form packaging boxes. However, the sheets <NUM> might generally be made of e.g. paper, cardboard, foil, a composite material thereof or any other material routinely used in the packaging industry.

The sheet processing machine <NUM> comprises a series of processing stations that are juxtaposed but interdependent one another in order to form a unitary assembly. The processing machine <NUM> includes a loading station <NUM> followed by a cutting station <NUM> (also usually named punching station) comprising for example a die or platen press <NUM> where the sheets <NUM> are transformed by cutting, a waste removal station <NUM> wherein most of the waste parts are stripped, a blank separation station <NUM> (also usually named reception station) for separation of the blanks <NUM> (or blanking operation) by means of a blanking tool <NUM> and an evacuation station <NUM> for removing the residual waste sheets of the punched sheets <NUM>.

The number and nature of the processing stations may vary depending on the nature and the complexity of the converting operations to be carried out on the sheets <NUM>.

The sheet processing machine <NUM> also has a transfer mechanism <NUM>, which in the shown embodiment is a conveyor, to make it possible to individually move each sheet <NUM> from an outlet of the loading station <NUM> to the evacuation station <NUM>.

The conveyor uses a series of gripper bars <NUM> that are mounted so as to be moveable by means of two loops of chains <NUM> one placed laterally on each side of the sheet processing machine <NUM>. Each loop of chains <NUM> travels around a loop which allows the gripper bars <NUM> to follow a trajectory passing successively by the cutting station <NUM>, the waste removal station <NUM>, the blank separation station <NUM> and the evacuation station <NUM>.

Each gripper bar <NUM> travels on an outward path in a substantially horizontal plane of passage between a driven wheel <NUM> and an idler wheel <NUM>, and then a return path in the top portion of the sheet processing machine <NUM>. Once returned to the driven wheel <NUM>, each gripper bar <NUM> is then able to grip a new sheet <NUM> at a front edge of the sheet <NUM>.

In <FIG>, each processing station is illustrated in the form of two rectangles symbolizing respectively its top portion and its bottom portion that are positioned on each side of the plane of movement of the sheets <NUM>.

In <FIG>, a transverse (or lateral), longitudinal and vertical direction are indicated by the orthogonal spatial system (T, L, V).

The terms "upstream" and "downstream" are defined with reference to the direction of movement of sheets <NUM> in a handling direction as illustrated by the arrow D in <FIG>.

The sheet processing machine <NUM> further comprises a device <NUM> for determining the height of a sheet pile in a receiving area <NUM> of the blank separation station <NUM>. Accordingly, the sheet pile is a pile of blanks <NUM> in the shown embodiment.

The device <NUM> is connected to a control unit <NUM>, e.g. by an Ethernet connection, the control unit <NUM> being adapted for controlling the device <NUM>. However, the device <NUM> could also be connected to the control unit <NUM> by any means which provides a sufficiently fast exchange of signals between the device <NUM> and the control unit <NUM>. , the connection can also be established wireless, e.g. by Wi-Fi.

The control unit <NUM> further comprises a storage module <NUM>.

The sheet processing machine <NUM> further comprises a human-machine-interface <NUM> which in the shown embodiment is a touch-sensitive display.

By the human-machine-interface <NUM>, a (not shown) operator can control the operation of the sheet processing machine <NUM>. Further, information about the current status of the sheet processing machine <NUM> can be displayed on the human-machine-interface <NUM> to inform the operator.

In <FIG>, a perspective view of the device <NUM> is shown.

The device <NUM> comprises a first sensor element <NUM> arranged at a first side <NUM> of the receiving area <NUM> and a second sensor element <NUM> arranged at an opposite side <NUM> of the receiving area <NUM> such that the first sensor element <NUM> and the second sensor element <NUM> are opposite each other along a width direction of the receiving area <NUM> which in the shown embodiment corresponds to the transverse direction T (see <FIG>).

The first sensor element <NUM> comprises a light emitting source <NUM> and the second sensor element <NUM> comprises a light receiving sensor <NUM>.

In principle, the light emitting source <NUM> and the light receiving sensor <NUM> could also be swapped, i.e. the first sensor element <NUM> could also comprise the light receiving sensor <NUM> and the second sensor element <NUM> could comprise the light emitting source <NUM>.

When the light emitting source <NUM> and the light receiving sensor <NUM> are facing each other as shown in <FIG>, a light barrier <NUM> is formed between the light emitting source <NUM> and the light receiving sensor <NUM>. Accordingly, any interruption of the light barrier <NUM> can be registered based on the sensor signal of the light receiving sensor <NUM>.

The first sensor element <NUM> is mounted to a first rail <NUM> and the second sensor element <NUM> is mounted to a second rail <NUM>, wherein the first rail <NUM> and the second rail <NUM> are parallel to each other and to a length direction of the receiving area <NUM> which is perpendicular to the width direction of the receiving area <NUM> and which in the shown embodiment corresponds to the longitudinal direction L.

The first rail <NUM> and the second rail <NUM> are mounted to a first frame <NUM> and a second frame <NUM>, respectively. The first frame <NUM> and the second frame <NUM> are connected to the blank separation station <NUM>. Accordingly, the device <NUM> is suited to be retrofittable to existing sheet processing machines <NUM>.

In principle, the first frame <NUM> and the second frame <NUM> could also be parts of the blanking separation station <NUM> instead of being parts of the device <NUM>.

<FIG> shows a side view of selected parts of the device <NUM> of <FIG>.

From <FIG> it becomes apparent that the first sensor element <NUM> is mounted by a slotted guide slider <NUM> in a slotted guide <NUM> of the first rail <NUM>. Accordingly, the first sensor element <NUM>, and therefore the light emitting source <NUM> (see <FIG>) are displaceable along the length direction of the receiving area <NUM> as indicated by the double-arrow P<NUM> shown in <FIG>.

More specifically, the first sensor element <NUM> is manually displaceable along the length direction of the receiving area <NUM> by the operator, i.e. the first side <NUM> of the receiving area <NUM> is arranged at an operator side of the sheet processing machine <NUM> which can be easily accessed by the operator.

The second sensor element <NUM> comprises an actuator <NUM>, rendering the second sensor element <NUM> automatically displaceable along the length direction of the receiving area <NUM> as indicated by the double-arrow P<NUM> in <FIG>.

The opposite side <NUM> of the receiving area <NUM> is arranged at an opposite operator side of the sheet processing machine <NUM> which cannot be easily accessed by the operator.

In the following, the mode of action of the sheet processing machine <NUM> in regard to the device <NUM> will be discussed in more detail.

For preparing the sheet processing machine <NUM> for a sheet processing job, the operator sets the sheet processing machine in a set-up mode via the human-machine-interface <NUM>. This change in operation mode is registered by the control unit <NUM>. In principle, the device <NUM> could also be used analogously without entering a specific set-up mode.

Next, the operator manually displaces the first sensor element <NUM> along the length direction of the receiving area <NUM> by shifting the slotted guide slider <NUM> along the slotted guide <NUM> to a target position.

The target position is chosen such that, during operation of the sheet processing machine <NUM>, when blanks <NUM> are collected in a pile of blanks <NUM> in the receiving area <NUM> up to a target height, at least a part of the uppermost blank <NUM> of the pile of blanks <NUM> is at the same position along the length direction of the receiving area <NUM> as the light emitting source <NUM> of the first sensor element <NUM>.

With other words, if the blanks <NUM> in the pile of blanks <NUM> do not extend over essentially the complete length direction of the receiving area <NUM>, the first sensor element <NUM> is placed by the operator at a position in which the blanks <NUM> will be present.

The control unit <NUM>, which is connected to the first sensor element <NUM> and to the second sensor element <NUM>, registers that the first sensor element <NUM> has been moved and starts to automatically displace the second sensor element <NUM> along the second rail <NUM> by controlling the actuator <NUM> for finding a working position of the second sensor element <NUM>.

To determine the working position, the light receiving sensor <NUM> transmits its sensor signal at every position along the second rail <NUM> to which the second sensor element <NUM> has been moved by the control unit <NUM>.

The control unit <NUM> stores the received sensor signals together with the associated position along the second rail <NUM> in the storage module <NUM>.

When the light emitting source <NUM> and the light receiving sensor <NUM> are facing each other, the light barrier <NUM> is formed (see <FIG>), resulting in a non-zero sensor signal from the light receiving sensor <NUM>. The better the alignment of the light emitting source <NUM> and the light receiving sensor <NUM>, the higher the resulting sensor signal will be, i.e. the maximum sensor signal is indicative for the best alignment between the light emitting source <NUM> and the light receiving sensor <NUM>.

Therefore, the working position is determined by the control unit <NUM> by identifying the position of the second sensor element <NUM> along the second rail <NUM> at which the received associated sensor signal has been maximum. Therefore, the second sensor element <NUM> is moved to this position along the second rail <NUM>.

Afterwards, the control unit <NUM> transmits a message to the human-machine-interface <NUM> to inform the operator that the device <NUM> has been properly set up and the light barrier <NUM> has been successfully formed.

Therefore, the operator can change the sheet processing machine <NUM> from the set-up mode to an operation mode in which the sheets <NUM> are processed to form blanks <NUM> which stack to a pile of blanks <NUM> in the receiving area <NUM>.

During the operation of the sheet processing machine <NUM>, the first and second sensor elements (<NUM>, <NUM>) work in an intermittent fashion: when the sheet processing machine ejects a blank, the sensor elements are temporarily disabled for the time the blank needs to cross the light barrier. The remaining time, the light receiving sensor <NUM> is receiving constantly or at least once per pre-determined time unit, for example once per <NUM>, transmits the current sensor signal to the control unit <NUM>. Advantageously, the light receiving sensor comprises several sensor cells disposed one above the other to precisely determine the height of the uppermost blank <NUM>.

As soon as the pile of blanks <NUM> reaches a height at which the uppermost blank <NUM> is at the same height as the light barrier <NUM>, the light barrier <NUM> will become interrupted and the sensor signal of the light receiving sensor <NUM> will drop, especially drop to a value of zero or at least to a value corresponding to the noise level of the light receiving sensor <NUM>.

This change of the sensor signal is registered by the control unit <NUM>. The control unit <NUM> is adapted to transmit a message to the human-machine-interface <NUM> that the height of the pile of blanks <NUM> has reached the height of the light barrier of the device <NUM>.

Preferably, this height corresponds to a target number of blanks <NUM> such that the operator can stop the operation of the sheet processing machine <NUM> and remove the produced blanks <NUM> from the blank separation station <NUM>.

In principle, the control unit <NUM> can also be adapted to automatically stop the operation of the sheet processing machine, once the light barrier <NUM> becomes interrupted.

For the next sheet processing job, the operator can again enter the set-up mode and manually adjust the position of the first sensor element <NUM>, if necessary, and repeat the above described process.

In the embodiment described above, the device <NUM> for determining the height of the sheet piles is used to detect when a pile of sheets <NUM>, more specifically a pile of blanks <NUM>, is piled up which essentially corresponds to determine at which point in time during operation of the sheet processing machine <NUM> a certain number of blanks <NUM> have been produced.

However, the device <NUM> could also be used analogously to detect when a pile of sheet <NUM> becomes torn down, i.e. to detect when so many sheets <NUM> have been removed from the pile of sheets <NUM> that the height of the sheet pile is lower than the height of the light barrier <NUM>.

Claim 1:
Sheet processing machine comprising a receiving area (<NUM>) for collecting a sheet pile, characterized by further comprising a device (<NUM>) for determining the height of the sheet pile, wherein
the device (<NUM>) comprises a manually displaceable first sensor element (<NUM>) arranged at a first side (<NUM>) of the receiving area (<NUM>), and an automatically displaceable second sensor element (<NUM>) arranged at an opposite side (<NUM>) of the receiving area (<NUM>) such that the first and second sensor elements (<NUM>, <NUM>) are arranged opposite each other along a width direction of the receiving area (<NUM>),
the first sensor element (<NUM>) and the second sensor element (<NUM>) being displaceable along a length direction of the sheet receiving area (<NUM>),
wherein the first sensor element (<NUM>) is one of a light emitting source (<NUM>) and a light receiving sensor (<NUM>) and the second sensor element (<NUM>) is the other one of a light emitting source (<NUM>) and a light receiving sensor (<NUM>),
the light emitting source (<NUM>) and the light receiving sensor (<NUM>) forming a light barrier (<NUM>) along the width direction when facing each other.