Abstract:
An optoelectric safety system which protects a free entrance or access opening in a machine&#39;s protective housing or protective cage at all times during operation. The system includes a reflection light scanner on the machine frame above and adjacent the floor at the front of the machine in the vicinity of the entrance or access opening, which emits a scanning beam covering a horizontal or inclined area and which generates an inner permanent protective field and an outer dynamic protective field.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to an optoelectrical safety system for a machine that operates with at least some mechanically dangerous operating processes, in particular for a folding press, a system which protects a free entrance and/or access opening in the machine&#39;s protective housing or protective cage at all times during operation. The invention also relates to a method for the operation of the device. 
     Optoelectric safety systems, in particular safety light barriers, are widely used in industrial practice to indicate the penetration of people, human limbs, animals or objects into a protected or dangerous area. Typical applications of safety light barriers are, for example, the protection of people from injuries in the danger zone of machines, for example stamping presses, folding presses, lever linkages, casting machines, coil winding machines, robotic machinery etc. For the sake of simplicity, here and in what follows the main functional equivalents of ultrasound, camera image, heat image and similar protective systems will be summarised under the term “optoelectric safety systems”. 
     A safety system for a folding press or a similarly functioning machine is described in EP, A1 0264349. In this a bundle of laser beams is sent from a transmitter on one side of the press to a receiver on the other side of the press. The bundle is routed parallel to the edge of the stamp and at distance δ from the sheet surface of the workpiece. In the folding operation the edge of the stamp is lowered in a vertical plane, which also contains the laser bundle. The speed of the stamp is measured by the bundle of laser beams and braked if a preset speed is exceeded. Because the distance δ of the laser bundle from the plate roughly corresponds with the thickness of a human finger, this safety measure should allow a finger to be withdrawn in good time. 
     EP, A1 0562726 describes a safety light barrier made up of at least two parts, which should detect the penetration of objects into a protected zone more effectively. The light barrier can, for example, be angled, with each segment consisting of a transmitter and receiver for an area protection system made up of a multi-beam light barrier. All transmitters and receivers of the segments are connected together in series, which should permit an angled layout to suit each individual case. 
     According to EP, A1 0264349 these and similar familiar systems are associated with a relatively large residual risk or in the case of EP, A1 0562726 require a complicated layout of safety light barriers, which hinders the free manipulation of machines. 
     The inventor has set himself the task of creating an optoelectric safety system of the type described at the start, which provides maximum safety, is flexible in use, is inexpensive and conforms to all legal standards. 
     With regard to the device, the task is solved according to the invention by the presence of 
     an approximately vertical column at either side of the entrance and/or access opening, each with a transmitter or receiver for a safety light barrier in the form of a multi-beam protective field covering an area, 
     a reflection light scanner above the floor at the front of the machine in the vicinity of the entrance and/or access opening, covering a horizontal or inclined area, with specifiable inclination and/or geometry, which generates an inner permanent and an outer dynamic protective field. 
     specific and further variants of the protective system are the subject of the dependent patent claims. 
     The combination of an approximately vertical safety light barrier forming the first protective field and at least one preferably semi-circular area generated by a reflection light scanner forming the second protective field with an inner permanent and outer dynamic area provides ideal conditions that have never been achieved before with regard to safety and optimal operating processes, which can be further improved by preferred measures. 
     An optoelectric, but also a functional equivalent safety system as described above can be used in a large number of industrial machines with at least one dangerous operation. Examples are listed above. Particularly important are folding presses, for example program controlled bending presses, and machines with similar operation. 
     Safety light barriers themselves are known, for example from EP, A2 0281747. A safety light barrier is made up in the form of a multi-beam protective field covering an area, whereby the distance between individual beams is as laid down in the specifications. If one or more of the light beams is interrupted an electrical signal is generated which, via an actuator, triggers a machine stop, for example, or a change in the working speed, possibly to creep speed, or a visual and/or acoustic signal. 
     The reflection light scanner using light time measurement is also in itself familiar, for example from the EP, A2 0281748. With a radius of around 15 m a semicircular area totalling 350 m2 can be covered. Within this area Pcs can be used to define two protective fields as required: 
     In a secure protective field, the danger zone, a person can be detected and a dangerous machine movement stopped immediately. 
     In an adjacent warning protective field a warning signal can be triggered if a person is detected outside the actual danger zone. 
     Unlike the safety light barrier, a reflection light scanner does not use a transmitter/receiver, and it does not need a reflector. An extremely short pulse of light is emitted and directed via a rotating mirror, thus covering a semicircular area as described. At the same time an electronic time measurement process is initiated. If the scanning beam encounters an obstacle, the diffuse reflected light is detected by a sensor and at the same time the time or distance measurement stopped. The distance to the diffuse reflecting object is calculated from the time difference between the transmitted and received impulse and a predetermined zone allocated (safe protected field, warning protective field, outside monitoring zone). By this means the protective field can be precisely adapted to the danger zone, the installation cost is lower and there are no mechanical devices to obstruct work. 
     The resolution of the safety light barrier and the reflection light scanner in the danger zone is such that a finger-sized penetrating object can trigger a signal, therefore the resolution will preferably be at least around 15 mm, in particular at least around 10 mm. This provides the greatest possible safety, the danger zone generally ends 30-40 cm from the machine part with a dangerous movement, meaning that for there to be any danger an entire hand, not just one finger, must be placed in the danger zone, before there is danger of injury. A hand, knee or foot exceeds the minimum resolution capacity by several times. 
     Folding presses and similarly functioning sheet processing machines have vertically and laterally adjustable consoles to hold the workpiece, which protrude into the protected danger zone. Individual light beams from the safety light barrier must therefore be masked so that the folding press can be operated with a workpiece inserted. Therefore penetration openings, preferably lined up, are blanked out for at least some of the beams from the safety light barrier, guaranteeing unimpeded passage. The consoles may optionally be made of transparent material at least in the area of light penetration. Suitable consoles in this context consist for example of Plexiglas or another transparent, mechanically strong plastic. 
     The two columns that generate the safety light barrier are mounted on a base plate or directly upon the floor, as appropriate, by screws for example. This sets firstly the distance from the machine and secondly the width of the light barrier. These upright columns obstruct the function of the protective field generated by the reflection light scanner, depending upon the cross-section of the column an inactive “shadow” shaped like the sector of a circle is generated. Clearly, the closer a column is placed to the reflection light scanner, i.e. to the machine, the larger is this shadow. However, there are other factors in favour of placing the columns as close to the machine as possible. 
     Therefore, in a particularly advantageous design variant of the invention the columns have a greatly reduced cross-section in the area of the protective field of the reflection light scanner in the direction of the scanning light beam. In practice, this is achieved in one of the first variants by making perforations in the direction of the light beam, particularly from slits running along the columns in the longitudinal direction. According to a further variant the columns can be completely split in the area in question and the two parts held apart by at least three or four rods. For reasons of stability one or two connecting rods are less favourable, their effective cross-section would be greater than is the case for three or four thinner rods statically well distributed over the cross-section. It should also be noted that as many rods as possible should be aligned with each other in relation to the light beam. If there are three rods only two are hit by the light beam, the third lies in the “shadow” of another rod. 
     The length of the perforations or the rods is optimised with regard to the stability of the upright columns and the adjustability of the protective field of the reflection light scanner, taking into account the size of the safety light barrier. 
     If appropriate, the columns are connected to their footplate via a lockable spherical adjuster. This allows optimal adjustment within a suitably limited angular range. Such spherical adjustment mechanisms are known. The preferred all-round adjustment angle β in relation to the vertical is a maximum of around 10°. 
     According to a further special design variant of the invention the protective field of the reflection light scanner is not horizontal, but is specified as a diagonal plane at a suitable angle a of 10-45°, in particular 10-30°, in relation to the horizontal. The reflection light scanner is fastened onto the machine housing or machine frame at the appropriate angle. Installation generally takes place directly above the floor on the front of the machine. The inclined path of the protective scanning field increases the possibilities for adding further peripheral devices and guarantees a large amount of working freedom for the operator. The angle of this area forming the protective field can be adjusted either manually by familiar mechanical means or using programmed actuators. Although the protective field is generally semicircular, it can have any desired geometric shape. 
     As mentioned above, the reflection light scanner defines a safe protective field in the danger zone, which is referred to here as the inner permanent protective fields. This can be freely defined within a semicircle of diameter 8 m, for example. An object protruding into this area immediately triggers the stopping of the dangerous work operation at the machine or at least its dramatic slowing to a creep speed of around 10 mm/sec. An outer dynamic protective field from the reflection light scanner adjoins the inner permanent protective field. This is also freely definable within a semicircle with a diameter of, for example, 30 m with the aid of light time measurement. When an object penetrates the outer dynamic protective field an alarm may be triggered and/or the working speed of the machine markedly reduced, for example in a folding press the stamp is only lowered at the above-mentioned speed of just 10 mm/sec. 
     Further safety measures can be employed by the use of integrated mechanical guards in addition to the area of the inner permanent protective field of the reflection light scanner. In special cases the inner permanent protective field of the reflection light scanner can also be replaced by this mechanical system. 
     In principle, the optoelectric safety system is independent of the machine type. It can easily be exchanged or retro-fitted. Particularly advantageous are machine independent standard components, which can even be designed as add-on modules. 
     With regard to the method, the problem is solved by the invention in that when the protective system is switched on the interruption of at least one unmasked light beam of the safety light barrier and/or diffused light in an unmasked reflection position of the scanner beam of the reflection light scanner generates an electric signal, which in turn triggers the actuator of a machine operating unit and/or an alarm. Special and additional design variants of this method are the subject of the dependent patent claims. 
     Machines equipped with a normal optoelectric safety system, in particular folding presses, have a manual operating mode selection switch, which is used to specify the machine speed during setting up, production etc. According to an advantageous further development of the invention the operating mode can be automatically determined when there is a certain transition from one protective field to the other. If the appropriate equipment is present a suitable protective field selection can also be detected automatically. 
     Furthermore, a CNC control with a variance comparison can be used for workpiece recognition. 
     The preferred light beams for use in the optoelectric safety system are laser beams, particularly those in the visible and IR range. 
     SUMMARY OF THE INVENTION 
     The main advantages of the invention can be summarised as follows: 
     A protective field directly above floor height at the front of the machine, in combination with a safety light barrier offers the greatest possible safety combined with significantly more free space for movement. 
     The options for adding further peripheral devices are significantly improved. 
     Reduced cross-section or interrupted columns permit an expansion of the protective field of the reflection light scanner. The protective system can be designed as an add-on unit for various machine types. 
     The protective system can be adapted to all national statutory regulations. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be explained in more detail based upon the design examples represented in the drawing. The following are shown schematically: 
     FIG. 1 A side view of a folding press shown as a bending press with two light barriers (state of the art) 
     FIG. 2 A further development of FIG. 1 in accordance with the invention with a safety light barrier and a reflection light scanner, 
     FIG. 3 A view of a folding press with optoelectric safety system, 
     FIG. 4 A horizontal projection in accordance with FIG. 3, 
     FIG. 5 A side view in accordance with FIGS. 3 and 4, 
     FIG. 6 A slightly angled column, and 
     FIG. 7 The effects of split columns of a safety system. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 depicts a state of the art folding press  10  with an outlined machine frame  12  and a protective housing or protective cage  14 , also in outline only. 
     A tool holder  18  is fastened to the lower yoke  16 , and the dies  20 , for example with v-shaped longitudinal grooves, are clamped into this. A tool holder  24  is attached to an upper yoke  22  for a stamp  26  that can be lowered with great pressure and precise path definition, which is angled in the working area and ends in a wedge-shaped stamp edge  28 . 
     There is a workpiece  30  on the die  20 , a metal sheet that has already been bent once. 
     At least two consoles  32  to hold the workpiece  30  are coupled to the machine frame  12  so that they move longitudinally, these consoles also move vertically, as indicated by arrows  33 . 
     An optoelectric safety system for the folding press  10  incorporates a vertical light barrier  34  with parallel beams which are around 15 mm apart, running perpendicular to the drawing sheet and are shown rotated. These beams  36  are transmitted from the first column  38  on one side of the machine and received by a second column  38  on the other side of the machine. The safety light barrier  34  completely covers the access opening  40  in the protective housing  14  of the machine. 
     A second light barrier  42  of the safety system, slightly inclined in relation to the horizontal, is depicted in the same way as the vertical light barrier  34 , it runs at an angle to this. The operator&#39;s freedom of movement is clearly greatly restricted by this. 
     According to the instantaneous view in FIG. 1, both light barriers  34  are inactive. The operator&#39;s forearm  44  is reaching through the vertical light barrier  34  and interrupting the beam  36 , which is shown as a dotted line in this area. The folding press  10  is already switched off or set to creep speed. 
     In the vicinity of the console  32  the beams  36  are masked so that these do not switch off the machine or even not allow it to start up in the first place. 
     The lower light barrier  42  is also inactive, because the beams in the area of console  32  are not masked and/or the operator&#39;s leg has penetrated this protective field. 
     In the design format according to the invention shown in FIG. 2, the lower, angled light barrier  42  is missing in comparison with FIG.  1 . On the machine frame  12  next to the floor a reflection light scanner  46  is positioned such that it covers an inclined, preferably semicircular, area. The protective field  48  this creates is at an angle α to the horizontal of around 20°. Width b 1  forms an inner permanent protective field  50 , the adjoining width b 2  forms an outer dynamic protective field  52 . 
     When the scanning beam of protective field  48  encounters the operator&#39;s trousers  54  a diffuse reflection is created, a very small part of the beam emitted by the reflection light scanner  46  returns to a receiver, where it is detected and evaluated. 
     The consoles  32  have a longitudinal slit as a penetration opening  34  for the beams  36  of the safety light barrier  34  in this area. 
     FIGS. 3 and 4 show the layout of the columns  38  generating the safety light barrier  34  and the reflection light scanner  46 . The columns  38  incorporate a footplate  58  separated by three small cross-section rods  56 . Thanks to the split columns  38  the protective field size is increased by the shaded area shown in FIG.  4 . 
     The electronics are contained in a monitor  70  with screen and operating unit which is coupled to the machine frame  12  by a swivel arm  68 . 
     The division of the columns  38  is more easily recognisable from FIG.  5 . Despite their small cross-section the three rods  56  form a stable connection to the footplate  58 . The rods  56  are arranged so that the scanning beam  59  (FIG. 7) of the protective field  48  can also hit a column  38  next to it with little loss. The diffusion radiation generated by the rods  56  is masked. 
     A column as shown in FIG. 6 can be used more flexibly because it is connected to its footplate  58  via a lockable spherical adjuster  60 . The angle of adjustment β in relation to the vertical is just under 5°. 
     FIG. 7 shows the protective field  48  running diagonally upwards from a reflection light scanner  46  with a scanning beam  49  running through it in the area behind the column  38 . Both columns are in accordance with FIG. 6. A column  38  in the vicinity of the reflection light scanner  46  without a division or narrowing in the area of the protective field  48  would throw a broad shadow, indicated as a shaded area, an inactive sector-shaped zone of angle δ. The rods  56  (FIG. 6) throw two significantly smaller shaded shadow fields  62 ,  64 , whereby the third rod lies in shadow field  62  and does not generate its own shadow. 
     In the column  38  away from reflection light scanner  46  the rods are not aligned, therefore three very narrow shadow fields  66  are generated. The angle δ of a column  38  without a reduction in cross-section in the field of protective field  48  would be much smaller here, roughly comparable with the shadow fields  62 ,  64 .