Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
1999-10-07
2001-06-05
Hofsass, Jeffery (Department: 2632)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S557000, C250S559120, C250S559130, C250S559150
Reexamination Certificate
active
06243011
ABSTRACT:
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'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 &dgr; 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 &dgr; 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the plate roughly corresponds with the thickness of a human finger, this safety measure should allow a finger to be withdrawn in good time.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 reflecti
Bachman & LaPointe P.C.
Hofsass Jeffery
Pham Toan
Sick AG
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