The invention relates to a clamping system for a press brake or folding press, the clamping system comprising a beam for holding one or more tools.

Press brakes are machines used for bending or folding sheet material, such as metal sheets. For that purpose, press brakes include a bottom beam and a top beam, which are movable with respect to each other. The top and bottom beams both hold tools, between which a workpiece is provided for bending. In general, bending tools of a press brake are exchangeable to allow making different types of bends or folds, and to allow servicing the tools. Therefore, press brakes are provided with a clamping system which can releasably clamp the tools. Clamping systems may be provided on the top beam of the press brake, on the bottom beam, or on both. Clamping systems extend over substantially the entire width of the press brake, while individual tools normally extend over only a part of the press brake width. A tool of a specific size may be selected for a specific workpiece to be bent or folded. Multiple tools can be placed at various positions in the clamping system to perform different bending or folding operations.

Two types of press brakes can be distinguished. The first type has a clamping system that is an integral part of either the top or bottom beam. A further clamping system may or may not be provided for the other of the top or bottom beam. Such a clamping system, that is an integrated one, can not be detached from its top or bottom beam, and is itself thus not exchangeable with another clamping system, whereas the tools the clamping system can hold are exchangeable. The second type has an exchangeable clamping system that can be fixedly connected to either the top beam or the bottom beam. A further clamping system may or may not be provided for the other of the top or bottom beam. The exchangeable clamping system allows exchanging tools, but can also be detached from its top or bottom beam, for instance for maintenance or for exchanging it for another clamping system. This is used in the art to make one press brake suitable for different tooling types, which may require different clamping systems, and/or to service the clamping system.

Further clamping systems exist that can be clamped by other clamping systems as if they were a tool. Such clamping systems can for instance be clamped by a system for tools of a first type, whereas they themselves can clamp tools of a second type, so that such clamping systems act as an adaptor between a clamping system and a tool that would otherwise be incompatible. The invention relates to clamping systems integrated with press brakes, be it the bottom beam or top beam, exchangeable clamping systems, and clamping systems acting as an adaptor. Similarly, the invention can be applied to folding presses.

In order to make a desired bend or fold, it is important the press brake is fitted with the right tool, and that the tool is at the right position along the longitudinal direction of the beam.

For that reason, a system capable of identifying and localizing tools known as TIPS marketed by the applicant has become popular. Some details of the TIPS system have been disclosed in EP 1 864752 Al. EP 1 864752 A1 discloses in figure 3 a method of positioning, defined in the current application as “to determine the position of’, a tool by emitting light towards the tool using light-emitting devices 12 and receiving reflected light using light-receptive sensors 11.

Although the method of using emitters and receivers is effective for positioning and identifying tools, there is a desire for improvement of said method. In particular, the accuracy of positioning is limited by the size of emitters and sensors. In theory accuracy can be improved by using a larger number of emitters and sensors in different positions. However, the maximum usable amount is limited by space available on the tool and on the beam. As such, the accuracy of the positioning system presented in EP 1 864752 Al has an upper bound.

Moreover, the system of EP 1 864752 Al allows identification of a limited amount of types of tools. However, the system is limited in the amount of recognizable patterns. Thus, there is also a need to improve the system of EP 1 864752 Al by allowing identification of more patterns. The ability to identify more patterns may for instance allow the identification of individual tools, instead of simply the type of tool.

It is therefore an object of the invention to improve the existing clamping system by allowing a greater positioning accuracy and/or a larger amount of information to be read from a tool.

Said object is achieved by a clamping system according to the preamble, which has a first and a second transducer, each being capable of transducing electrical energy to light and vice versa, the first and second transducers each being configured to transmit light towards, and to receive light from, the one or more tools held by the beam

By using transducers which can both emit and receive light, it becomes possible to first produce light with the first transducer and receive preferably the same light, albeit reflected, with the second, and to repeat the process vice versa. As such, two measurements can be taken with the same transducers. The two measurements may be used in conjunction to increase the amount of information on the tool and the position thereof. Since the two measurements can be made with the same components, relatively little space is needed for the components. Accordingly, more information may be encoded on the same amount of space, which may facilitate identification of a particular tool instead of merely its type. Further or alternatively, positioning may become more accurate, as the resolution is increased by placing a relatively large amount of transducers on a relatively small space.

In particular, the use of visible light is envisioned. However, the invention could be applied with other forms of light, such as UV-light and infrared right. UV-light is herein defined as having a wavelength of between 100 nm and 400 nm. Visible light is herein defined as having a wavelength of between 400 nm and 780 nm. Infrared light is herein defined as having a wavelength of between 780 nm and 1000 pm. As such, light is herein defined as having a wavelength of between 100 and 1000 nm.

It is noted that there need not be an unobstructed path between the transducers and the tool. In fact, any object that is transparent or otherwise permeable to the used light may be placed in between without compromising operation of the clamping system. This characteristic may be advantageously employed by applying a cover over the transducers, the cover being transparent to at least the light produced by the transducers, so as to protect the transducers from inadvertent impacts. A particularly suitable cover may be made of Gorilla Glass as marketed by Corning Inc. of New York, United States (www.corning.com), or a similar type of chemically strengthened glass.

Transducer as used herein refers to a single active component taken in isolation, i.e. not to a system composed of multiple components. Thus, according to the invention the same component that converts light to electricity also converts the electricity to light. This is exactly why fewer components may be needed than the traditional case, in which one component detects light and the other emits it.

The transducers may be part of a sensing system including additional emitting and receiving components, preferably exclusively including other similar or identical transducers.

The transducers may cooperate with each other for detecting the same tool. As such, the transducers may be arranged together in a single clamping system, such as that of/for either an upper beam or a lower beam of a press brake or folding press. The transducers may be arranged close to each other, such as adjacent to each other. In practice, the transducers are arranged on the same beam (i.e. on the upper beam or on the lower beam, or on the clamping system thereof). The transducers may be arranged on a shared circuit board. The transducers may be arranged along a receiving space for receiving a tool. As will be explained below, the transducers can be arranged in particular inside the receiving space.

The clamping system as described in the preamble may be a clamping system for either the upper beam or the lower beam of the press brake or folding press. It is noted that although both beams often include clamping systems, they are not collectively referred to as a clamping system. In fact, the two clamping systems of a press brake operate independently. The invention may be applied to a press brake or folding press including two clamping systems as described in the claims. In particular, the two clamping systems may be an upper and a lower clamping system respectively.

The transducers may be arranged so as to cooperate for detecting a tool. Light emitted by one transducer may be reflected by the tool and received by the other, and vice versa.

In particular, the at least two transducers may be LED’s. LED’s can suitably be used to produce light at a relatively high efficiency. The photoelectric effect exhibited by LED’s may be used to configure the LED as a transducer for generating a current when light shines on the LED. As such, a LED can be used both as a sensor and as an emitter. The use of LED’s is especially advantageous in the current application, as LED’s can be relatively small, thereby allowing a larger amount of LED’s in the same space.

In particular, red LED’ s may be used, for instance having a wave length of approximately 630 nm.

In one embodiment, the clamping system further comprises a controller for controlling the first and second transducers. Using such a controller, use can be made of the characteristics of the transducers.

In particular, the controller may be configured to send an electrical signal to the first transducer while receiving an electrical signal from the second transducer during at least a first interval.

During said interval, the first transducer is used as an emitter, while the second transducer is used as a sensor. Light produced by the first transducer may be reflected by the tool onto the second transducer. As such, the second transducer may sense certain characteristics of the tool. In the first place, the presence of a reflection may indicate the presence of a tool. Moreover, as certain surface characteristics of the tool may influence characteristics of the reflected light, information may be gained on the surface of the tool from the reflected light.

The controller may be further configured to receive an electrical signal from the first transducer while sending an electrical signal to the second transducer during a second, different interval.

In such a situation, the function of the emitter/sensor is opposite to that described above. As a result, the path taken by light and reflected light is opposite to that presented earlier. In some cases, the information obtained in this way may be the same information as during the first interval, therewith confirming a prior measurement. In other cases, the surface of the tool may differently affect the characteristics of the reflected light. Thus, by using the two transducers alternatingly as sensor/transmitter, a larger amount of information can be obtained without requiring additional components. As no additional transducers are required for obtaining the additional information, no further space is required for said further transducers.

In order to further increase accuracy and/or the amount of information the system can receive, the system may comprise a plurality of first transducers. Accordingly, the controller may then be configured to:

- send an electrical signal to the plurality of first transducers while receiving an electrical signal from the second transducer during at least another, third interval, and/or

- send an electrical signal to the second transducer while receiving an electrical signal from the plurality of first transducers during at least another fourth interval.

Emitting light with and or receiving light from multiple first transducers allows receiving light reflected by different portions of the surface of the tool. Accordingly, a larger amount of light may be received leading also to an increased amount of information that can be determined from the reflected light. Effectively, such an embodiment allows many-to-one communication and or one- to-many communication, respectively.

Said effect may be further employed when the system also comprises a plurality of second transducers, wherein the controller is configured to:

- send an electrical signal to the plurality of first transducers while receiving an electrical signal from the plurality of second transducers during at least another, fifth interval. In such a configuration, many-to-many communication can take place, thereby greatly enhancing the amount of information that can be obtained from the totality of reflected light.

In another embodiment of the clamping system, the controller is configured to send an electrical signal to at least one of the first and the second transducer, and at the same time receive an electrical signal from the same at least one of the first and the second transducer.

In such a configuration, a single transducer is used both as emitter and as sensor. Accordingly, the amount of emitting and receiving components is doubled without requiring more components.

Principally, it is possible to receive the light of the at least one transducer at another component and/or to receive light that was emitted by another component at the at least one transducer. It is however also possible to receive light reflected by the tool, but emitted by the same at least one transducer.

In order to distinguish between the origin of light from different emitters, they may be controlled to or be configured to emit light with mutually different characteristics. In particular, the frequency or intensity may mutually vary. Additionally, a variation in time of for instance the intensity may be used to give a particular emitter unique characteristics. As an example, emitters may be distinguished from each other if they blink at different frequencies.

The skilled person will appreciate that the terms ‘first’ and ‘second’ relating to the transducers herein are used only to distinguish between the transducers. In fact, the transducers need not be different in kind or type. As such, a plurality of the same or similar transducers may be used in the clamping system as described herein.

In order to provide the functionality described above, the controller may be configured to alternatingly select different ones of the plurality of transducers as the first or second transducers. As such, one of the transducers may act as the first transducer at one point in time, and act as the second transducer at another point in time. Moreover, multiple transducers may be selected as first and/or second transducers. Accordingly, providing a plurality of transducers and selecting first and second transducers as desired allows operation of the system in many different operating modes, each giving rise to information that would otherwise be unobtainable. As such, a system with multiple transducers that are controlled to switch their functionality is very versatile and may further increase accuracy of the amount of encodable information. Selecting one or more transducers as the first or second transducers need not be a separate act. In fact, controlling the transducers as described above is regarded as having selected those transducers in accordance.

In yet another embodiment of the clamping system, the controller is configured to control the first and/or the second transducer to transmit light at different intensity levels.

The larger the intensity of the light, the larger the surface of the tool that will reflect back sufficient light to be detected. As such, by varying the intensity of the emitted light, a selection can be made between which parts of the tool are seen. As an example, first a relatively small part of the tool can be sensed by using a relatively low intensity. Then, a larger part of the tool can be sensed by using a relatively high intensity. As the larger part of the tool would normally include the smaller part, the influence of the newly sensed areas can be determined by appropriate signal processing.

The controller may be configured to determine a characteristic of an electric signal received from the first and or the second transducer, the characteristic being for instance a power, a frequency, a voltage or a current level.

The controller may accordingly be used to digitize the received signal. The digitized signal may comprise information on the characteristics, so that signals with different characteristics can be distinguished. This may allow processing the signals so as to determine information on the basis of the characteristics.

In particular, the characteristic may be a voltage level. The voltage may be measured over a resistance, preferably an Ohmic resistance, which is fed by a current provided by the transducer receiving the light.

In a particular embodiment of the clamping system, the first and second transducers are configured for transmitting light at mutually differing wavelengths.

By transmitting light at mutually differing wavelengths, light emitted from different transducers may be distinguished, even after being reflected by the tool. Additionally or alternatively, the different wavelengths may interact differently with the surface of the tool. As such, probing the tool with different wavelengths may allow retrieving a larger amount of information. Practically, the beam of the clamping system comprises a longitudinal receiving space for receiving at least a part of the one or more tools when held by the beam, and wherein the first and second transducers are arranged in the receiving space.

In such a practical embodiment, the transducers can be placed close to the tool and may therefore easily be able to sense it. Moreover, light from the outside might be at least partly prevented from entering the receiving space by the wall thereof and by the tool. Accordingly, influence of outside light on the transducers is reduced, which accordingly reduces noise in the signal generated by the transducers. Additionally or alternatively, placing the transducers in the receiving space puts them in a relatively protected area, so that the transducers are less likely to be damaged by a workpiece being bent or by other impacts from the outside.

Particularly suitable locations for the transducers are at a side or a blind end of the receiving space as seen in cross section thereof. At such locations, the transducers are clear of forces from the beam tot the tool which are needed for operating the press brake.

In the case the clamping system comprises a plurality of transducers, such as a plurality of first and/or second transducers, the transducers may be arranged in a matrix. The matrix may be two- dimensional.

A relatively large surface area can be covered by such an arrangement. The transducers may be arranged in staggered and or slanted rows and or columns. A staggered or slanted matrix may allow compensating for any misalignment between the transducers and particular features on the tool. Additionally, a staggered or slanted matrix guarantees an alignment of some, but misalignment for some other transducer with respective features on the tool. The misalignment, in particular the amount thereof, has an effect on the received light. Said effect may be used to enhance accuracy of the localization using reflected light.

Of course it is also possible to create a slanted and/or staggered shape of features on the tool, when the transducers are aligned in a right-angled matrix. Further, both may be slanted/staggered at different angles. The effects described-above will remain unchanged.

The invention also relates to a clamping system as described above, with a tool, wherein the tool comprises a marking having encoded therein at least an identification number. The identification number may be usable to uniquely identify the particular tool. As such, no two tools may have the same identification number. The identification number may take the form of a serial number. Being able to uniquely identify particular tools is of use in tracking the performance of a tool for e.g. maintenance or billing purposes.

The marking on the tool may have features of a characteristic dimension similar to or larger than a dimension of the first and/or second transducer.

If the features is similar in size to, or larger than, the transducer, it becomes relatively easy to detect the feature. In particular, the features may have a characteristic size that is approximately half that of the transducers. In such a configuration, it can be guaranteed at least one transducer is completely aligned with a feature.

The marking may comprise features distinguishable by a surface characteristic, such as colour, roughness, reflectance or angle.

Differences in such features will affect the reflection of light differently. Accordingly, the features can be detected using reflected light. Moreover, these surface characteristics may be made relatively easily on a tool, for instance using a laser.

As an example, the greyness or grayscale of the surface could be used as a feature, i.e. the colour could be varied from light grey to black continuously or in the desired amount of discrete steps.

As a first option, the surface characteristic is continuously variable. Optionally, the encoding is analogue. Accordingly, a relatively large amount of information may be stored using a single characteristic. As an example, a colour varying from light-grey to pitch black may be used to represent a continuous variable, or a variable with a relatively large amount of discrete points, as opposed to a binary encoding.

As a second, alternative option, the identification number of the marking is encoded in a discrete code. Such a code may be relatively easy to sense or process.

It is preferable the code is of a higher ordinal than two, e.g. a ternary, quaternary or quintary code, or a code of a higher ordinal. As such, a relatively large amount of information may be stored in a single characteristic. As an example, a code of order n may be achieved by providing a code having features coloured at n different grey levels. The invention also relates to a tool for use in a press brake, the tool comprising a marking having encoded therein at least an identification number, the marking being configured to reflect light received from the first and second transducers.

The tool may have all the above described features, alone or in any suitable combination. The tool may provide the corresponding advantages.

The invention will be further elucidated with reference to the drawings, in which corresponding elements have reference numerals increased by 100, and in which: Figures 1 A and IB schematically show a side and a front view respectively of a press brake;

Figures 2A schematically shows a perspective view of a clamping system with a tool partially received therein, tilted to show its top surface;

Figure 2B schematically shows a cross section of the clamping system of figure 2A with its tool, now inserted into the clamping system;

Figures 3 - 8 and 15A - 15B schematically show cross sections of variations of the clamping system;

Figures 9A and 9B schematically show two transducers and a tool in cross section;

Figures 10A and 10B schematically show a marking that can be arranged on a tool; Figures 11 A and 1 IB schematically show arrays of transducers; and

Figures 12A - 14B schematically show different ways of operating the transducers.

Throughout the figures, like elements are referred to using like reference numerals. Like reference numerals of different embodiments are increased by one hundred (100).

Figures 1A and IB show a press brake 1 placed on a ground surface G. The press brake 1 includes a top beam 2 and a bottom beam 3. The top beam 2 is provided with a top clamping system 4. The top clamping system 4 releasably holds a top tool 5. The bottom beam 3 is provided with a bottom clamping system 6, which releasably holds a bottom tool 7. The top and bottom clamping systems 4, 6 each extend over substantially the entire width W of the press brake 1. The top and bottom tools 5, 7 are shown to extend over only part of the width W. Consequently, they may be moved to different positions in longitudinal direction L of the top and bottom clamping systems 4, 6.

Multiple tools may be arranged end-to-end in order to provide a greater working width. Alternatively, different tools may be placed at various positions to allow multiple bending or folding operations to be performed without exchanging tools in between operations. The top beam 2 and the bottom beam 3 are moveable towards and away from each other in the direction of arrow M by means of hydraulic systems 8, although another type of drive system could be used. To this end one of the beams 2, 3 may be movable while the other beam may be stationary, or both beams 2, 3 may be movable. Accordingly, the top and bottom tools 5, 7 are also moveable towards and away from each other. To bend sheet metal, the sheet is inserted between the tools 5, 7 which are then moved towards each other. The top tool 5 then forces the sheet metal into the bottom tool 7 in order to deform the sheet metal by bending. After bending, the tools 5, 7 are moved away from each other by moving the top beam 2 via the hydraulic systems 8. The clamping systems 4, 6 are releasably attached to the top and bottom beam 2, 3 respectively via a suitable locking system. Accordingly, the clamping systems 4, 6 can be exchanged for clamping systems suitable for other tools, or the clamping systems 4, 6 can be taken out for servicing them.

Although not shown, the features described below in relation to the exchangeable clamping systems 4, 6 can also be applied to other types of clamping systems 4, 6, e.g. of the integral or adaptor type.

Figures 2A and 2B show a clamping system 104 for a press brake 1. The clamping system comprises a beam 111 for holding tools 105. The beam 111 comprises a longitudinal receiving space 109 embodied as a slot parallel to the length of the beam 111. The tool 105 is held by the clamping system 104 by placing an adaption 112 thereof in the receiving space 109, and consecutively clamping the adaption 112 of the tool 105 at recesses 110 provided for that purpose. The illustrated adaption 112 with its recesses 110 forms part of a so-called “New Standard style” clamping system. Other clamping systems and techniques for holding tools exist, like e.g.

American style and European style. The current disclosure is not limited to the exemplary clamping system described with reference to the figures, but may be more universally used in other clamping systems.

The clamping system 104 further comprises a circuit board 113 with an array of transducers 114 arranged thereon, which will be described in more detail with reference to figures 9 - 14B. The transducers 114 are used to localize and identify the tool 105. For this purpose, the circuit board 113 of figures 2A and 2B is arranged in the receiving space 109. In particular, the circuit board 113 is arranged at the blind end of the receiving space 113, in a recess 123 allowing a surface of the circuit board 113 to lie flush with the blind end of the receiving space. The tool 105 is provided with a marking 115 comprising surface features 116. When the tool 105 is placed in the receiving space 109, the marking 115 faces the circuit board 113, so that the transducers 114 are near the marking 115. The circuit board 113 extends along the longitudinal direction of the beam 111. Accordingly, the tool 105 can be sensed using the transducers 114 regardless of its position in the beam 111. It is noted that for the sake of clarity, not all transducers 114 and surface features 116 have been provided with their own reference numeral. Although not shown here, the circuit board 113 with its transducers 114 may be protected by a transparent cover at least partially closing off the recess 123.

Variations as to the position of the transducers 114 are possible. As a non exhaustive list of examples, reference is made to figures 3 - 8 and figures 15A - 15B. Figures 3 and 4 each show a clamping system 204, 304 for a top beam 202, 302 (not shown), each having a corresponding receiving space 209, 309 (substantially taken up by the tool 205, 305). The transducers 214, 314 (not visible) are provided on circuit boards 213, 313, which in the illustrated embodiments are arranged in recesses 223, 323 in sidewalls of the corresponding receiving spaces 209, 309. As such, the transducers 214, 314 face a side of the tool 205, 305 when it is placed in the receiving space 209, 309.

Further, figures 5 - 8 show clamping systems 406, 506, 606, 706 for bottom beams 419, 519, 619, 719. The clamping systems 406, 506, 606, 706 comprise corresponding receiving spaces 409, 509, 609, 709, for receiving an adaption 412, 512, 612, 712 of a tool 407, 507, 607, 707. Although it is possible to clamp the tool 407, 507, 607, 707 in the receiving space 409, 509, 609, 709, it is envisioned the tool 407, 507, 607, 707 is configured to rest with shoulders 417, 517, 617, 717 on a top surface 418, 518, 618, 718 of the bottom beam 419, 519, 619, 719. Figures 5, 6 and 7 show that the circuit board 413, 513, 613 carrying the transducers may be arranged in the receiving space 409, 509, 609, for instance in a sidewall thereof (figures 5 and 7) or in a blind end thereof (figure 6). As an alternative, which is shown in figure 8, the transducers may also be arranged on a circuit board 713 on the top surface 718 of the bottom beam 719, so that a shoulder 717 of a tool 707 comes to lie over the circuit board 713 when the tool 707 is held by the clamping system 706. In each of these embodiments the circuit board 413, 513, 613, 713 is shown to be arranged in a recess 423, 523, 623, 723, although that is not strictly necessary for the circuit board 513 in the embodiment of figure 6, which might simply be mounted at the bottom of the receiving space 509.

Figures 15A and 15B show clamping systems 804 in top beams 811 for holding shoulder bearing tools 805. Tools 805 of this kind comprise shoulders 817 which support against surfaces 818 of the beam 811. As shown in figures 15A and 15B respectively, the circuit board 813 may be arranged in such a surface 818 of the beam 811 on the front and back side of the beam 811. Accordingly, the marking 815 on the tool is provided on the shoulder 817 of the tool 805 corresponding to said surface 818.

As can be deduced from the figures discussed above, the transducers 14, 114, etc. can be placed anywhere on or in the clamping system 4, 6, 104, 106, etc. that allows the transducers 14, 114 etc. to see the tool 5, 7, 105, 107, etc. when it is held by the clamping systems 4, 6, 104, 106, etc. The marking 15, 115, etc. can be arranged on a corresponding part of the tool 5, 7, 105, 107, etc.

It is noted that transducers 14, 114, etc. need not necessarily be placed on a circuit board 13, 113, etc.

The functioning of the transducers 14 is explained with reference to figures 9 A, 9B and further.

The features described herein can be applied to any clamping system 4, 6. For the sake of brevity, only the reference numerals of the first embodiment are used for these and the following figures.

The transducers 14 comprise a first transducer 20 and a second transducer 21, arranged together on a circuit board 13. Although only two transducers 14 are shown as an example here, more transducers 14 may be employed. The transducers 14 are arranged on the clamping system 4 so that they will align with a marking 15 provided on a tool 5 when the tool 5 is held by the clamping system 4. In Figures 9A and 9B, two variations of the adaptation 12 of the tool 5 are shown as I and II on either side of a dotted line S. The left-hand variation I comprises a recess 90 machined in the surface of the adaptation 12 to provide a flat surface. The marking 15 (shown herein as a dotted line) is provided in this recess 90 on the flat surface thereof. In the right-hand variation II, the marking 15 is provided directly on the surface of the adaptation 12. As such, it is clear the marking 15 may be provided directly on the tool 5 without additional machining steps, or such steps may be used if desired. In this example, the transducers are LED’ s that produce light of a visible red color. The clamping system 4 also comprises a controller 22, which is connected to the circuit board 13 in order to control the transducers 20, 21. At a first point in time, shown in figure 9A, the first transducer 20 can be turned on the by the controller 22, in order to shine light (dashed arrow) onto the tool 5 at the location of the marking 15. The marking 15 reflects the light (dashed arrow) back, onto the second transducer 21. The controller 22 is configured to measure a signal generated by the second transducer 21 in response to the received light (dashed arrow). In particular, the controller operates by measuring a voltage across a resistance fed by a current produced by the second transducer 21. As the measured voltage corresponds to the reflected light, which is affected by the marking 15, information on the marking 15 is determined by analysis of the measured voltage. At another point in time, shown in figure 9B, the same system can be used another way. In particular, the second transducer 21 may be turned on the shine light (dashed arrow) onto the marking 15. As shown in figures 9A and 9B together, the function of the transducers can be changed from emitter to receiver. Other functionalities of the transducers will be described below.

First however, reference is made to figures 10A and 10B which respectively show markings 15-1 and 15-2. Each marking of figures 10A and 10B corresponds to only a part of a complete marking 15. Accordingly, break lines are used to indicate the marking may continue in the left and right direction of figures 10A and 10B. Thus, a complete marking 15 may have a generally longitudinal shape, which may extend over the tool in the length direction of the beam in which it is to be clamped. The marking 15-1 of figure 10A comprises, as an example, twenty features 16. In practice, a marking 15 may have many more features 16. The features 16 are shown to differ mutually by providing them with a different line pattern. In practice, the features 16 can be made distinguishable by locally changing a surface characteristic of the tool. For example, the features may comprise a distinct surface roughness levels. In figure 10A, six different line patterns are shown. It is possible to for instance choose six different surface roughness levels. Information can be stored in the marking 15 by setting the particular roughness level of each feature 16. In this example, a discrete encoding of the 6 ^th order, i.e. having six different possibilities for each feature 16, can be used to encode an identification number uniquely identifying a tool.

As an alternative, a continuously variable surface characteristic, such as a grey value can be chosen for each feature 16. This is shown in figure 10B using features with mutually different amounts of lines. In principle, it is possible to vary the grey value continuously. As such, it is not necessary to use discrete levels for encoding.

It is noted that other surface characteristics may be used to represent the features 16, and that discrete encoding can be done using any desired order.

Figures 11 A and 1 IB show transducers 14 arranged in matrices on circuit boards 13. Although a relatively small part of a circuit board 13 is shown in the figures, a larger circuit board 13 may be employed as indicated by the break lines. In practice, a circuit board 13 may have many more transducers 14. It is envisioned the circuit board 13 will be longitudinal in shape, so as to be arranged parallel to the longitudinal direction on a beam of a clamping system, as shown in figure 2 A. The circuit board 13 may be the circuit board of the embodiments described in relation to figures 2A - 9B. The matrix of figure 11 A is right angled, meaning the transducers 14 are substantially aligned in both the direction of the rows R and the columns C. The transducers 14 may however also be aligned in a staggered matrix as shown in figure 1 IB, where each row R is displaced with respect to the previous row R, so that the columns C are slanted. Although twenty transducers 14 are shown here, other amounts of transducers can be used.

Figures 12A - 14B show different ways of operating the same transducers 14. First, figure 12A shows a single first transducer 21 emitting light, and eight neighboring transducers operating as second transducers 22 receiving light. The controller can thus receive information from second transducers 22 receiving reflected light. As the light was emitted by a single first transducer 21, figure 12A represents a one-to-many configuration. Figure 12B on the other hand shows a many- to-one configuration, with multiple (in this example eight) first transducers 21 emitting light, and a single receiving second transducer 22. Each transducer, even the first transducers 21 emitting light, can be used at the same time as a receiver 22 for receiving reflected light. The reflected light may origin from itself or from another transducer.

Figure 13 A shows a first situation, wherein a first transducer 21 emits light at a first intensity level. Reflected light is received at multiple, but not all second transducers 22. At another moment in time, shown in figure 13B, the first transducer 21 emits light at a higher intensity, so that more light is reflected. Accordingly, more second transducers 22 can be used to receive reflected light.

Figures 14A and 14B respectively show that at different moments in time a different transducer 14 can be used as first transducer 21 or second transducer 22. Thus, depending on the operation mode, a transducer may be controlled to emit light, receive light or both.

Although the invention has been described hereabove with reference to a number of specific examples and embodiments, the invention is not limited thereto. Instead, the invention also covers the subject matter defined by the annexed claims.

As an example, clamping systems for press brakes have been shown, but the invention could equally well be applied to folding presses. Moreover, specific types of clamping systems have been shown, whereas the invention could be applied to other types of clamping systems within the scope of the attached claims. As a particular example, a clamping system for a top beam with a shoulder- supported tool, as is known in the art, could also be provided with the features of the main claim.