Light curtain simplifies press safety

Machine builders understand that to design truly safe machines, safety systems have to anticipate both accidental and deliberate circumstances that may injure operators and bystanders. However, reconciling that design imperative, which adds cost and complexity, with competitive price pressures and customer demands for machines that allow quick setup and changeover, is not an easy task.

Scientific Technologies Inc. (STI) understands these competing design issues and offers industrial OEMs and safety system retrofitters some additional help. STI’s multisegment Type 4 safety light curtain, the newest member of the MiniSafe 4700 family of light curtains,the MiniSafe Flexible MSF4700, offers a design that allows machine builders to implement unique configuration combinations and protect up to four different openings by connecting as many as four housings in sequence.

Protected heights from 150–1,800 mm and resolutions of 14, 20 and 30 mm are available, with any combination among those dimensions possible. This ability to customize height and resolution for each light curtain segment permits precise fitment. “For example,” says STI’s Kent Beall, product manager, Optical Safety Products “an application where a 14-mm finger detection segment is required for the vertical plane, and a second 30-mm detection segment is required to sense the presence of someone standing in a hazardous area, is possible without having to resort to multiple machine safeguards.”

The MSF4700 is engineered to withstand high shock and vibration environments typical of punch presses and other heavy industrial machinery. “When we set out to design the MSF4700, we knew we had the challenge of taking the electro-optic assembly of our smaller profile product (the MCF4700) and create a package that could survive the tough environments found in  metal-forming and other industries,” says Beall. “Initially we characterized these abusive environments by taking measurements of the acceleration--shock and vibration--that the light curtain would experience. Then we acquired test equipment to reproduce these environments in the lab. This allowed us to try several solutions before selecting the one to thoroughly ‘ruggedize’ the MSF4700.”

One of the big advantages of light curtains is that they allow quick, convenient access to a machine without having to resort to physical barriers to guard its hazardous elements. How close the protective plane of the light curtain is to the point of hazard is calculated from various standards (ANSI B11.19-1990, EN 999).

A key element in this safe mounting distance equation is the response time of the light curtain. The faster the light curtain, the closer it can be mounted to the point of hazard. “The MSF4700 is very fast with a response time range from 6.7 msec for a seven-channel system to only 32 msec for a 256-channel system,” says Beall. “The combination of fast speed and large number of sensor segment sizes allow for a real custom fit.”

The control box is available in either DIN-mount or 14-gauge steel and allows fixed blanking which permits programming from either the front cover of the steel enclosure or by a remote keyswitch. “We knew this new feature was important to the metalforming industry where performing a quick changeover from job to job needs to be done expeditiously,” says Lazzara. With the program keyswitch, an object such as a fixture required for a new job can be placed in the protected field, with the rotation of the supervisor-controlled keyswitch, the light curtain can continue to guard the various machine setups.

STI engineers found that individual beam indicators (IBIs) that glow bright red once the beam is broken is a valuable feature. The IBIs are helpful when setting up or aligning the light curtain and when fixed blanking is selected. “During fixed blanking the IBIs will light if the expected blockage is not present,” explains Beall. “An additional aid in setup and maintenance is the two-digit display found on the controller. This display communicates the various operational status of the light curtain system, and describes faults that have occurred.”