TECHNICAL FIELD

The invention concerns in general the technical field of clipping device. Especially the invention concerns control of the clipping. BACKGROUND

Clipping of a sheet-like object, such as a veneer, may be performed with multiple types of clipping devices. One traditional type of clipping device is so called guillotine type clipper wherein the clipping of the object is performed with a knife operating in a guillotine fashioned. Another type of clipping device is so called rotary clipper wherein the knife is arranged to rotate along its axis and wherein the rotation of the knife is adjusted to the speed of the object in the production line. The rotation of the knife causes the clipping of the object.

The rotary type of clipper is known from a feature that the clipping cycle is at least partly dependent on the rotational speed of the knife. When the clipping cycle is constant the operation of the clipper is easy to implement. However, in sophisticated production lines it shall be possible to produce products comprising different sizes, such as pieces of veneer with different widths when cut from a veneer mat whose length is defined by a length of a log from which the veneer mat is produced. In such a case it may happen that a new clipping signal is given before the previous clipping cycle is completed. As the clipping cycle is constant i.e. the rotational speed of the knife is constant, it is impossible to operate the clipper in such a manner that shorter products may be produced.

Thus, there is need to establish a solution which enables adjusting the clipping cycle so that it widens the applicability of rotary clippers for different needs.

SUMMARY

An objective of the invention is to present methods and control units for generating a velocity profile for a rotational knife in a clipper. Another objective of the invention is that the methods and the control units for generating a velocity profile for a rotational knife takes into account at least some parameter relating to a clipping cycle in the generation of the velocity profile. The objectives of the invention are reached by methods and control units as defined by the respective independent claims.

According to a first aspect, a method for generating a velocity profile for a rotational knife in a clipper is provided, the method comprising: receiving a clip signal for a second clipping cycle; detecting a phase of a first clipping cycle in response to the receipt of the clip signal for the second clipping cycle; generating the velocity profile of the second clipping cycle for the rotational knife, the generated velocity profile being at least partly dependent of the detected phase of the first clipping cycle. Further, the generation of the velocity profile of the second clipping cycle may be performed as follows: when the clip signal is received during a period of time 0< tc2 < T(B), generating a higher speed portion to the velocity profile of the knife; when the clip signal is received at the instant of time tc2 = T(B), generating a similar velocity profile as the previous velocity profile; and when the clip signal is received during a period of time tc2 > T(B) and Vk > 0, generating a lower speed portion to the velocity profile of the knife; wherein tc2 = instant of time of the clip signal, T(B) = point of time when the knife starts decelerating in the first clipping cycle and Vk is a rotational speed of the knife.

In addition, the method may further comprise a step of controlling a velocity of the rotational knife in the clipper according to the generated velocity profile.

According to a second aspect, a control unit for controlling a velocity of a rotational knife in a clipper through a velocity profile for a clipping cycle is provided, the control unit comprising a processor and a memory storing portions of computer program code, wherein the control unit is caused to: receive a clip signal for a second clipping cycle; detect a phase of a first clipping cycle in response to the receipt of the clip signal for the second clipping cycle; generate the velocity profile of the second clipping cycle for the rotational knife, the generated velocity profile being at least partly dependent of the detected phase of the first clipping cycle. The control unit may be configured to generate the velocity profile of the second clipping cycle by: when the clip signal is received during a period of time 0< tc2 < T(B), generating a higher speed portion to the velocity profile of the knife; when the clip signal is received at the instant of time tc2 = T(B), generating a similar velocity profile as the previous velocity profile; and when the clip signal is received during a period of time tc2 > T(B) and Vk > 0, generating a lower speed portion to the velocity profile of the knife; wherein tc2 = instant of time of the clip signal, T(B) = point of time when the knife starts decelerating in the first clipping cycle and Vk is a rotational speed of the knife.

According to a third aspect, a method for generating a velocity profile for a rotational knife in a clipper is provided, the method comprising: determining a clip time of a first clip cycle comprising a first velocity profile of the rotational knife; comparing the determined clip time to a predefined clip time; generating a velocity profile of the rotation knife for a second clipping cycle on the basis of the comparison.

The generation of the velocity profile of the second clipping cycle may be performed as follows: when tc(real) > tc, generating a higher speed portion to the velocity profile of the knife; when tc(real) = tc, generating a similar velocity profile as the first velocity profile; and when tc(real) < tc, generating a lower speed portion to the velocity profile of the knife.

In addition, the method may further comprise a step of controlling a velocity of the rotational knife in the clip-per according to the generated velocity profile.

According to a fourth aspect, a control unit for controlling a velocity of a rotational knife in a clipper through a velocity profile for a clipping cycle is provided, the control unit comprising a processor and a memory storing portions of computer program code, wherein the control unit is caused to: determine a clip time of a first clip cycle comprising a first velocity profile of the rotational knife; compare the determined clip time to a predefined clip time; generate a velocity profile of the rotation knife for a second clipping cycle on the basis of the comparison.

The control unit may be configured to generate the velocity profile of the second clipping cycle by: when tc(real) > tc, generating a higher speed portion to the velocity profile of the knife; when tc(real) = tc, generating a similar velocity profile as the first velocity profile; and when tc(real) < tc, generating a lower speed portion to the velocity profile of the knife.

According to a fifth aspect, a method for generating a velocity profile for a rotational knife in a clipper is provided, the method comprising: generating a first velocity profile according to the method as defined in the context of the first aspect above; generating a second velocity profile according to the method as defined in the context of third aspect above; and combining the first and the second velocity profiles by summing them. According to a sixth aspect, a control unit for controlling a velocity of a rotational knife in a clipper through a velocity profile for a clipping cycle is provided, the control unit comprising a processor and a memory storing portions of computer program code, wherein the control unit is caused to generate the velocity profile with the method as defined in the context of the fifth aspect above.

The exemplary embodiments of the invention presented in this patent application are not to be interpreted to pose limitations to the applicability of the appended claims. The verb "to comprise" is used in this patent application as an open limitation that does not exclude the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF FIGURES

The embodiments of the invention are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings.

Figure 1 illustrates schematically a clipper according to an embodiment of the invention.

Figures 2A and 2B illustrate schematically an operation of clipper according to an embodiment of the invention. Figure 3 illustrates an example of a velocity profile. Figures 4A-4C illustrates examples of velocity profiles generated according to a method of the invention.

Figure 5 illustrates schematically a control unit according to an embodiment of the invention. DESCRIPTION OF SOME EMBODIMENTS

The present invention especially relates to controlling an actuating motor of a clipper as depicted in Fig. 1 . The clipper 100 comprises a first roll 1 10 and a second roll 120 which may be covered in a wear material. A rotational knife 130 belonging to the clipper 100 is positioned between the rolls 1 10, 120 so that the first roll 1 10 is an anvil roll below the knife 130 and the second roll 120 is a supporting roll above the knife 130. The knife 130, or blade, is configured to be rotated along an axis essentially parallel to an axis of the anvil roll. The axis refers to a shaft through which the knife is rotatable. At least one edge of the knife is prepared for clipping, e.g. sharpened in an applicable way. In a clipping position the edges of the knife 130 are configured to extend to rolls so that the upper roll 120 supports the upper edge of the knife and the lower edge in the clipping position hits the anvil roll 1 10. The knife is preferably tensioned between the mounting points in order to reduce sag. Further, the rotation of the rolls and the rotation of the knife are achieved by arranging motors 140, 150, 160 to provide necessary force to the mentioned elements. For example, both rolls may have their own motors 140, 150. Additionally, the knife 130 may be equipped with at least one motor 160, but preferably with two motors at both ends of the shaft of the knife. The control of the rotation of the elements, and thus the control of the mentioned motors and at least the knife motor(s), is arranged by means of a control unit 170, which is configured to monitor the operation of the system as a whole and to receive operational instructions from one or more external entities. The control unit 170 is further configured to generate control signals, i.e. clipping instructions, at least to the motor(s) 160 providing the rotational power to the knife. The motor providing the rotational power to the knife may, for example, be an AC servo motor or a dual AC servo motor. The object, such as a continuous veneer mat, to be clipped is referred with 180 in Fig. 1 .

Next the operation of the clipper is described in brief by referring to Figs. 2A and 2B. The object 180, such as veneer, to be clipped is input to the clipper by an external device, such as by a conveyor belt. The speed of the conveyor belt is known and adjusted with the application area. The anvil roll 1 10 is configured to be rotated with a predetermined velocity, which is adjusted according to the input velocity of the object 180 into the clipping device. The object 180 to be clip is transported from the external device between the anvil roll 1 10 and the knife 140. The knife 130 is configured to rotate in a direction of the object flow from an initial position (see Fig. 2a) to a clipping position, as illustrated in an exemplified manner in Fig. 2b. In the initial position the knife 130 is positioned, in the present example, essentially horizontally with respect to the object 180, i.e. knife plane is essentially parallel to the object plane input to the clipper. When the clip is to be performed the knife 130 is rotated into a vertical position and the rotation speed of the knife 130 is adjusted to be the same as the rotational speed of the anvil roll 120 during the clipping phase. As described, in the clipping position the knife hits, or "bites" the rolls, i.e. the anvil roll 1 10 and the upper roll 120, so that object 180 gets clipped (Fig. 2B). The rotating directions of the knife 130 and the rolls 1 10, 120 are described with the arrows in Figs. 2a and 2b. It is worthwhile to mention that the initial position of the knife 130 with respect to the object 180 may vary under the inventive idea of the present invention. In some implementation the initial position of the knife may be in a predetermined angle, such as 20 degrees, with respect to object 180 (i.e. the angle between the planes of the mentioned entities. This may help inputting the object to the clipper at least in some situations. The Figs. 2A and 2B illustrates the clipper and the clipping operation schematically and it does not necessarily comprise all elements being involved in the operation.

In order to tackle the challenges in producing objects of different widths the idea of the present invention is to enable an adjustment of the rotational velocity of the knife through a velocity profile of the knife. The velocity profile refers to drive instruction of the knife i.e. how the motor of the knife rotates the knife. Fig. 3 illustrates a typical velocity profile of the knife. The knife accelerates (a) from the initial position to a constant rotational velocity Vc (the point of time is referred with T(A) in Fig. 3) and the constant velocity is adjusted to the velocity of the anvil roll. During the constant velocity Vc in an instant of time tc the knife has reached the clipping position, i.e. is essentially perpendicular to the plane of the object to be clipped. After clipping the velocity of the knife starts decelerating (-a) from the point of time referred with T(B) in Fig. 3 until it reaches the initial position with zero velocity.

According to the present invention the velocity profile of the knife is configured to be adjusted between consequential clipping cycles. The adjustment of the velocity profile for a second clipping cycle, i.e. a cycle which is consecutive to a first clipping cycle, is performed in response to instant of time tc2 when a clip signal for the second cycle is received in the control unit from an external entity delivering the clipping instructions. The clip signal refers at least to an instruction to perform a clip. The external entity may comprise, for example, a detector, such as a camera or any other applicable sensor, such as one or more light sensors, which is arranged to monitor the object and to determine, together with an external computing unit, an appropriate clipping point. I.e. by means of the camera information a clipping signal may be generated and in response to a receipt of the clipping signal, the clipper is configured to perform the clip. The control unit may be configured to detect in which phase on the velocity profile the knife is when a new clip signal is received and in response to the detection the control unit may be configured to adjust the velocity profile accordingly. The velocity profile used in the control of the rotation of the knife is advantageously adjusted by modifying the velocity profile in the following way (tc2 refers to a received clip signal for the second cycle and Vk refers to a rotational speed of the knife):

• When the second clip signal is received before deceleration (0< tc2 < T(B)), the control unit is configured to generate a higher speed portion for the next velocity profile of the knife (see Fig. 4A).

· When the second clip signal is received at the deceleration (tc2 = T(B)) of the previous velocity profile, the control unit is configured to generate a similar velocity profile for the next velocity profile of the knife as to the previous velocity profile (see Fig. 4B).

• When the second clip signal is received during deceleration (tc2 > T(B) and Vk > 0 , the control unit is configured to generate a lower speed portion for the next velocity profile of the knife (see Fig. 4C).

The Figures 4A-4C are only examples and the values disclosed therein are only examples and are not limiting the invention anyhow. It becomes clear from the description herein and from Figures that the knife rotates 180 degrees between the two clips when the knife comprises two clipping edges. The angle of rotation is thus dependent on the number of clipping edges in the knife (e.g. 1 edge - 360 degrees, 2 edges - 180 degrees, 3 edges - 60 degrees, 4 edges - 90 degrees). Moreover, the control unit, or any other entity, may be configured to monitor a delay of the clip and in response to a detection of a delay, the control unit may be configured to adjust the generation of a clipping signal (e.g. generate in in advance) in order to take into account the delay. In some other implementations of the invention the same may be achieved by monitoring the conveyance of veneer mat in the clipper, which enables timing of a clip to a desired position in the veneer mat. These are non-limiting examples in adjusting the clipping optimally. Some aspects of the present invention are disclosed in the following items:

• A control unit is configured to control a motor, such as dual AC Servo motor, for rotating a knife, such as double edged knife, between upper and lower rolls to clip an object, such as a veneer. The control unit may be arranged to target the knife tip speed to match the anvil roll speed during a clip cycle. On a timed interval averaged velocity of the knife just prior to roll contact may be measured and averaged velocity of the knife during roll contact may be measured. In other words, the control unit may control the drive of the motor accordingly and as a result the drive may take care of the speed control of the knife in order to reach the desired clipping time and/or position.

• Clip time may be monitored by time sampling the knife position during the clip to detect a rotational position equal to vertical (roll contact). Positional information may be derived from the drive system of the motor providing the rotational force to the knife. In such an implementation one or more sensors are arranged in optimal positions of the motor in order to monitor the positional state. Alternatively or in addition, an applicable sensor may be arranged to the knife and/or to the knife axis and/or to the motor by means of which it is possible to obtain positional information of the knife itself. Proper control requires that the roll speed is to be matched with the input speed of the veneer and the desired clip time is known in order to ensure that veneer size clips are accurate and roll wear is minimal. There are occasions when another clip is requested prior to completing the first clip. In such a case, it is important that the speed matching and clip time remain the same. For this event special control may be put in place to ensure the time can be met and roll speed is still matched. Dependent on time and position of the second clip request, motion commands to the motor(s) may be used to vary the travel speed of the clipper knife in order to make up distant if required and revert back to roll matching profile before roll contact. Dependent on time and position of the second clip request, motion commands to the motor(s) may be used to vary the travel speed of the clipper knife in order to increase the time if required and revert back to roll matching profile before roll contact.

According to an aspect of the invention a rotational speed difference between knife tip and anvil roll may be eliminated during blade contact keeping total time of clipping cycle constant

According to a further aspect of the invention the monitoring of resultant knife tip speed and clip time may be used to automatically adjust a velocity profile of the knife with respect to clipping cycle.

Further, a velocity profile of the knife may be varied so that higher speed portion is generated for the rotation of the knife if the second clipping command, i.e. clip signal, is issued before velocity profile of previous clip has reached deceleration point.

According to some further aspect of the invention the monitoring results of the applied velocity profile may be used for automatically adjusting the next application of this second clip profile.

According to an aspect of the invention a velocity profile may be varied so that clipping cycle is continued at constant knife speed if the second clipping command is issued at the moment when velocity profile of previous clip has reached deceleration point.

According to still further aspect of the invention a velocity profile is configured to be varied so that lower speed portion is generated if the second clipping command is issued after velocity profile of previous clip has reached deceleration point but not end point yet.

The knife in the clipper may comprise 1 to 4 clipping blades.

According to some implementation of the invention the clipper may comprise anvil roll above and below the knife body. • According to some further implementation of the invention the clipper may comprise anvil roll only below the knife body.

• According to some implementation of the invention an outer surface of at least one of the rolls, i.e. anvil roll and/or supporting roll, used in the clipper may be metallic. Preferably at least one of the anvil rolls is coated with a material which is wear-resistant, i.e. durable, in the application area. Such coating material may e.g. be plastic or rubber.

Summarizing at least some aspects of the description above the generated velocity profile may be used in a generation of control signals to the at least one knife motor.

The present inventive idea relates also to a generation of the velocity profile of the knife in response to a detection of a deviation in a predetermined parameter relating to the clipping cycle. According to an embodiment of the invention the mentioned parameter is the clip time i.e. the period from the initial position of the knife until the clip (i.e. clip time tc). This is known and predefined system parameter, but there exists deviation in real life. The deviation is, among others, a result of wearing of different parts in the cutter, such as bearings, motor couplings, clutches and/or other parts. By determining the real clip time of a clipping cycle and by comparing it to the predefined system parameter one is able to detect if there is deviation between these two values. If the deviation exists in a certain clipping cycle, the control unit may be configured to adjust the next velocity profile in a following manner:

When the real clip time (tc(real)) is longer than the predefined clip time tc, the control unit is configured to generate a higher speed portion for the next velocity profile of the knife.

When the real clip time (tc(real)) is the same as the predefined clip time tc, the control unit is configured to generate a similar velocity profile for the next velocity profile of the knife as to the previous velocity profile.

When the real clip time (tc(real)) is shorter than the predefined clip time tc, the control unit is configured to generate a lower speed portion for the next velocity profile of the knife (see Fig. 4C). According to an embodiment of the invention a tolerance may be set for the measured clip time against the predefined clip time tc. This prevents unnecessary adjustment of the velocity profile.

Furthermore, in some embodiment it may be possible to generate a velocity profile which takes into account both the instant of time when the second clip signal is received and the real duration of the previous clipping cycle. This may e.g. be achieved by first determining the individual components for each of these and sum them up in order to establish a combined velocity profile.

According to still further embodiment of the invention it may be possible to utilize a velocity profile derived from some previous clipping cycle in any later clipping cycle, which situation corresponds to the one on which the velocity profile is derived. In other words, the invention is not only limited to adjusting the velocity profile between two consequential clipping cycles. For example, it may be possible to gather and store data and the velocity profiles on certain types of clipping cycles and adjust any velocity profile of any following clipping cycle in response to a detection of the type of the clipping cycle in question.

As mentioned the control unit generating the velocity profile for each the clipping cycle may be configured to receive clipping instructions from an external unit or even determine them by itself if and when necessary information is input directly in the control unit. The control unit may be configured to detect the operational states of the anvil roll and the knife and to control at least the velocity of the knife by adjusting the motor rotating the knife through control signals. The control unit may at least be configured to detect the phase of the previous clipping cycle when a new clip signal is received in the control unit and to generate an adjusted velocity profile for the knife for the second clipping cycle as described above. Furthermore, if the monitored parameter by the control unit is the real clip time tc(real), the control unit may be configured to determine the real clip time tc(real) value and to compare the value to the predefined clip time tc stored in the system, such as in the memory of the control unit. If there is deviation found, the control unit may be configured to generate an applicable velocity profile to the knife.

Fig. 5 illustrates an example of the control unit 1 70 according to the invention. The control unit comprises one or more processors 510 and one or more memories 520. The memory or memories 520 is configured to store portions of computer program code 525A-525N. By execution at least a portion of the computer program code by the processor 510 the control unit is configured to operate as described above. The control unit 170 comprises necessary interfaces in order to communicate with the entities as described. It is worthwhile to mention that the velocity profile and its adjustments has only effect to the velocity of the knife during the clipping cycle This has not any effect for velocities of the mentioned rolls. In the clipping position the rotational speed of the knife shall essentially be the same as the rotational speed of the anvil roll and thus the transport speed of the object in the production line. The invention relates also a clipper comprising a first roll and a second roll and the knife, and wherein the knife, i.e. the motor(s) of the knife, is configured to be controlled in the manner as described. The control unit as described may reside in the clipper, but also an implementation in which the control unit does not physically reside in the clipper, but is operatively coupled to the clipper, belongs under the inventive idea of the present invention.

Features described in the preceding description may be used in combinations other than the combinations explicitly described. Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not. Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not.