EP1178120B1

EP1178120B1 - Apparatus for removable fastening of flat articles, like leathers and similar to a work surface

Info

Publication number: EP1178120B1
Application number: EP01114830A
Authority: EP
Inventors: Gianni Gallucci
Original assignee: Teseo SpA
Current assignee: Teseo SpA
Priority date: 2000-07-04
Filing date: 2001-06-28
Publication date: 2006-08-09
Anticipated expiration: 2021-06-28
Also published as: EP1178120A3; ITBO20000393A1; ES2270925T3; DE60122068D1; EP1178120A2; ATE335856T1; ITBO20000393A0

Abstract

In an apparatus for removable fastening of flat articles (2) to a work surface (1) for a machine for processing flat articles, e.g. leathers, the work surface (1) includes a plurality of fastening elements (3), which are selectively connected to suction means by respective valve means (10) to set under a vacuum effect the articles (2). Each of the valve means (10) includes a throttle valve (12), operated by a direct-current motor (21). The apparatus includes also sensor means (23) for detecting the motor (21) supply voltage and detecting variations with respect to the nominal voltage due to the motor rotation. Furthermore, the apparatus includes a sensor (24) detecting the current flowing through the motor (21) for detecting a motor (21) stop situation which is a consequence of reaching one of the extreme positions full open (A) and full closed (B) by the throttle valve (12). <IMAGE>

Description

The present invention relates to working of flat articles like leathers and similar.
In particular, the present invention relates to an apparatus for fastening the above articles to a work surface so that they do not move during processing steps.
As it is known, substantially flat articles, like leathers and similar are usually subjected to cutting, drilling, die cutting and other operations. For this purpose, the articles to be worked are usually fastened removably to a suitable work surface.
Known type of work surfaces are connected to a vacuum source, so that the articles laying thereon to be processed are kept firm due to the action of the vacuum.
Obviously, the article is firmly kept on the work surface when the suction source is operated..
The work surface should be preferably as big as possible, so as to contain also those articles to be worked having large dimension.
Leathers to be cut or drilled have also irregular shape and leave anyway some free areas on the work surface.
Since to be effective, the suction means must perform their action on the whole working area, if the article does not cover the entire surface, operation of the suction means does not give the best effect.
To compensate for this fact, the suction means are considerably oversized, so that their action is not affected by non-effective operation determined in those areas of the work surface, which are connected to the vacuum source but not covered by the article and which are, consequently, in direct contact with the open environment.
A technical solution for outweighing this problem is described in the Patent for industrial invention No. 1.285.511 of the same Applicant.
According to this technical solution, the work surface is divided into a series of different elements, formed by square plates, situated one beside another.
Each plate has a cavity, set separately in communication with the suction source by respective aspiration channels.
Each aspiration channel includes a valve, operated selectively to set under vacuum only the areas covered by the article to be worked.
The shape of the article to be worked is detected by suitable sensor means, which can include a camera connected to a processor and a shape recognising program stored in the processor. Another prior art apparatus is disclosed in DE 195 21 616 C.
Although the above described technical solution has improved considerably the previously used techniques, some drawbacks still affect the fastening of the articles to be worked to the relative work surface.
Actually, the valves for setting under vacuum the single cavities of the work surface, are bistable, i.e. are capable of assuming only two stable configurations, open and closed, respectively, which does not allow to modulate the vacuum level in the single elements of the work surface.
The perimetral active elements, i.e. those elements on which the edges of the article to be worked are placed, are usually only partially covered by the article.
Therefore, the vacuum effect along the edges of the article is much smaller than the one obtained by the elements covered thereby.
This has not been found practical for fixing the article to the work surface in the best way.
Actually, the most effective solution for fixing the leather articles, also considering the dimensions of the suction means, consists in applying a vacuum of bigger value to the article edges, and a vacuum of smaller value to the inner parts thereof.
The main object of the present invention is to propose an apparatus for removable fastening of an article to be worked to a relative work surface, which can change the intensity of vacuum in each single element, or group of elements of the work surface.
Another object of the present invention is to propose an apparatus with a work surface applying a vacuum with possibility to change the intensity in a simple, reliable and particularly cheap way.
The above mentioned objects are achieved by the features of the independent claim, while preferred features are defined in the dependent claims
The characteristic features of the present invention, which will be apparent from the claims, are pointed out in the following description, with reference to the enclosed drawings, in which:

Figure 1 is a schematic view of the work surface divided in the elements;
Figure 2 is a schematic view of the work surface of Figure 1, with an article to be worked, which covers it partially;
Figure 3 is a schematic partially section view of a part of the work surface of Figure 1, obtained according to the present invention;
Figure 4 is a diagram of the approximate values of the feeding voltages of the valves operating means, in arbitrary scale;
Figure 5 is a diagram of the values of the currents circulating through the operating means of Figure 1, in arbitrary scale.

With reference to Figures 1 and 2, the reference numeral 1 indicates a work surface, integral with the proposed apparatus.
The work surface 1 supports an article 2 to be worked, e.g. a piece of leather to be cut or drilled.
The work surface 1 is divided into a series of fastening elements 3, arranged one beside another and covering the whole surface thereof.
The fastening elements 3 can be connected selectively, and especially singularly, to known suction means, not shown for sake of simplicity.
For this purpose, each fastening element 3 has a cavity 4 open to outside (Figure 3).
Moreover, each cavity 4 is singularly set in communication with the above suction means by a communication channel 5.
Valve means 10, situated within the communication channel 5, are operated by a control unit, to selectively set under a vacuum the cavities 4 of the fastening elements 3, which are covered by the article 2 at least partially.
The above mentioned valve means 10 include a flow regulator 11, situated within the communication channel 5, substantially including a throttle valve 12.
The throttle valve 12 can assume, in a substantial continuous way, a plurality of intermediate positions C, included between two extreme positions, namely an open position A and a closed position B, respectively.
The throttle valve 12 is operated by progressive operating means 20, to assume one of the above operative positions, on command of a control unit 90.
The control unit 90 is a substantially known element of the proposed apparatus, and usually includes an electronic device for data acquiring and processing, a series of connection and control interfaces, as well as programs suitably designed on purpose.
The above mentioned progressive operating means 20 include a simple, direct current electric motor 21, whose power is sufficient to operate the throttle valve 12.
The rotation direction of the motor 21 is determined by the polarity of its supplied continuous voltage Vcc and thus the motor can rotate in both rotation directions by simple polarity inversion.
Power transmission means 22 are situated between the throttle valve 12 and the motor 21.
The transmission means include a worm screw 26, fastened at the head of the shaft of the motor 21 and engaging with a toothed wheel 27, which is keyed to the rotation axis of the throttle valve 12.
The progressive actuating means 20 include also sensor means 23 for the motor 21 rotation.
The sensor means 23 include a sensor 23a for detecting a difference Vh, VI of the motor 21 supply voltage Vcc with respect to a nominal supply voltage Vn.
The sensor 23a is connected electrically to the above mentioned control unit 90 to send thereto a signal indicating that a difference has occurred.
Figure 4 shows a diagram of the trend of the supply voltage Vcc at the input of the motor 21 with respect to the time t, referring to motor different operation conditions.
In particular, the supply voltage Vcc is near to the 0 if the motor 21 is not operated (t<t0 and t>t2).
During the period comprised between t0 and t1, the motor 21 rotates and the supply voltage Vcc oscillates, around the nominal value Vn, between a maximum value Vh and a minimum value VI.
During the period comprised between the t1 and t2, the motor 21 is operated, but is stopped, since it is prevented from rotating because the throttle valve 12 has reached one of the limit positions A, B.
In this case, the supply voltage has a stable value, substantially coincident with the nominal voltage value Vn.
In Figure 4 there is shown schematically the above mentioned variations Vh, VI, however they are actually much more limited and present a different wave shape.
Likewise, the duration of the periods t0-t1 and t1-t2 has been chosen arbitrarily, as a mere example.
The real duration of these periods, like the width of the variations Vh, Vi and the value Vn of the voltage in the period t1-t2, are in fact functions of different parameters and operation situations.
They are not important for the understanding of the present invention and will not be analysed any further in the following.
The above mentioned variations Vh, VI are substantially due to the fact that, during each complete rotation, current effectively flows through the the motor 21 only in the rotation portions in which the collector brushes and lamellas are in touch.
Although the supply voltage Vcc is stabilised, the absorption differences cause minimal changes of the nominal supply voltage Vn, which can be detected by the above mentioned sensor 23a.
Actually, for the invention purpose, it is enough that the sensor 23a detects only one variation Vh, VI.
It can be easily performed by simple electronic devices, e.g. known configurations including operational amplifiers.
The frequency of the variation of the tension Vcc during one rotation of the motor 21 indicates the motor relative angular position.
Actually, starting from a known position (which can coincide with an extreme position A,B of the throttle valve 12), the number of variations Vh, VI supplies a quite precise indication of the rotation angle of the motor 21 shaft.
The progressive operating means 20 of the throttle valve 12 include also means 24 for detecting at least one extreme position A, B of the throttle valve 12.
The detecting means 24 include a detector 24a of current I, aimed at detecting variations Ib of current I flowing through the motor 21 with respect to nominal current In (Figure 5).
The detector 24a is connected electrically with the above mentioned control unit 90, to send thereto a signal indicating the above variations.
Figure 5 is a diagram of the trend of the current I flowing through the motor 21 in relation to the time t, in different operation conditions thereof.
In particular, the operation conditions in different time periods taken into consideration, are the same as the ones already described for the supply voltage Vcc.
As it can be seen from the diagram of Figure 5, when the throttle valve 12 is in an extreme position A, B and the motor 21 is fed, the current I is considerably bigger than the nominal current In.
This change can be easily recognised and signalled to the control unit 90, e.g. by a simple electronic circuit of known configuration, including operational amplifiers.
Operation of the apparatus will be described in the following beginning from a situation, in which a flat article 2 e.g. a piece of leather, is placed on the work surface 1, so as to be worked.
The leather 2 covers a part of the work surface 1, and especially the perimetral areas of the leather occupy only partially some of the fastening elements 3.
In this situation, the suction means are deactivated and the control unit 90 does not feed the motors 21 for operating throttle valves 12 present in each fastening element 3.
The leather 2 position and shape are detected using known techniques, and on this basis, the fastening elements 3 wholly or partially covered by the leather 2 are recognised.
At this point, the control unit 90 commands a sequence of leather fastening operations for each fastening element 3.
The sequences are different for completely free fastening elements 3, partially covered and wholly covered by the leather.
If the fastening elements 3 are not covered by the leather 2, the control unit 90 operates the relative motor 21 in the direction of the throttle valve 12 closing, until the throttle valve reaches its closed position B.
At this point, the current sensor 24a recognises the increase of the flowing current I and the control unit 90 stops the motor 21.
If the fastening elements 3 are wholly covered by the leather 2, the control unit 90 operates the motor 21, until the throttle valve 12 reaches an extreme position, e.g. closing position B, which is detected, as already described above, by the current sensor 24a.
At this point, the motor 21 is operated in the direction of the throttle valve 12 opening.
The voltage sensor 23a detects the variations Vh, VI of the supply voltage Vcc.
The number of variations indicates the relative angular position of the motor 21 and sends information about the present position of the throttle valve 12 to the control unit 90.
Thus, the control unit 90 stops the motor 21 when the throttle valve 12 reaches an intermediate position C, in which it partially closes the communication channel 5.
Obviously, the partial closure of the communication channel 5 reduces the action of the suction means on the cavity 4 of the relative fastening element, and consequently, the obtained vacuum is less effective than the vacuum obtained with the open throttle valve 12.
Actually, a weak vacuum action in the inner areas of the leather 2 is advantageous, because it avoids leather deformations and keeps the power necessary for the suction means to keepthe leather fastened at the minimum.
The necessary vacuum level can be calculated empirically, and its value can be stored e.g. by suitable memory tables in the control unit 90.
If the fastening elements 3 are partially covered by the leather 2, the fastening sequence is quite similar to the one described for the wholly covered elements 3.
However, the relative motor 21 is stopped, when the throttle valve 12 is in the wholly open position A or in an intermediate position C, different from the previously mentioned one, corresponding to a more open position of the throttle valve 12.
The exact position of the throttle valve 12 stop depends on the percent of the fastening element 3 surface not covered by the leather 2.
If a larger part of the element 3 surface is not covered by the leather, the throttle valve 12 stops in a more open position, which corresponds to stronger suction action on the fastening element.
It is necessary in order to compensate for bigger vacuum effect losses provoked by the above surface not covered by the leather.
The above described sequence of leather fastening operations allows to obtain the best vacuum effect on all the parts of the article 2 to be fastened on the work surface 1.
This is a first, very important advantage with respect to the prior art, as it allows to avoid not homogeneous stresses of the article 2 and small deformations, which could jeopardise precision of further processing.
Another advantage derives from the fact that the suction means do not have to be oversized to compensate for vacuum effect losses and best use is made thereof constantly. This reduces the suction means production and maintenance costs.
A further advantage derives from the fact that the operative feeding power necessary for the suction means can be reduced, which results in reduction of the whole apparatus handling costs.

Claims

Apparatus for removable fastening of flat articles (2) to a work surface (1), said work surface (1) including a plurality of fastening elements (3), which are selectively connected to suction means by respective valve means (10), said valve means (10) being operated by at least one control unit (90) to set selectively parts of said articles (2) placed over said fastening elements (3) under the effect of a vacuum, said apparatus being characterised in that said valve means (10) include flow regulator means (11) and progressive operating means (20), aimed at bringing said flow regulator means (11) to a plurality of operative positions (A,B,C) comprised between an full open position (A) and a full closed position (B), with at least one stable intermediate position (C), which defines a corresponding partial vacuum effect for articles (2) placed on the fastening elements (3).
Apparatus, according to claim 1, characterised in that said progressive operating means (20) include: at least one direct-current motor (21); power transmission means (22) situated between said motor (21) and flow regulator means (11); sensor means (23) for detecting said motor (21) rotation; detecting means (24) for at least one of said extreme positions (A,B); said sensor means (24) and detecting means (24) being aimed at supplying said control unit (90) with information concerning the motor (21) rotation and reaching of at least one of said extreme positions (A,B).
Apparatus, according to claim 2, characterized in that said rotation sensor means (23) include a sensor (23a) for detecting variations of the motor (21) supply voltage (Vcc), said sensor (23a) being aimed at detecting periodical variations (Vh,VI) of said supply voltage (Vcc) with respect to a nominal voltage (Vn), said variations indicating the motor (21) rotation.
Apparatus, according to claim 2, characterised in that said detecting means (24) include a sensor (24a) of the circulating current (I), which is aimed at detecting variations (Ib) of said circulating current (I) with respect to nominal current (In), said variations (Ib) indicating when said flow regulator means (11) reach one of the extreme positions (A,B).
Apparatus, according to claim 2, characterised in that said power transmission means (22) include a worm screw (26), coaxial with the motor (21) shaft, and a toothed wheel (27), integral with said flow regulator means (11) and engaging with said worm screw (26).
Apparatus, according to claim 1, characterised in that it includes one valve (109 for each fastening element (3).
Apparatus, according to claim 1, characterised in that said flow regulator means (11) include at least one throttle valve (12), situated within a communication channel (5) between said fastening element (3) and said suction means.
Apparatus, according to claim 1, characterised in that said valve means (10) include a plurality of said operative intermediate positions (C), corresponding to different opening angles of said flow regulator means (11) and to different vacuum levels of said fastening elements (3).