Should we integrate safety in all machine automation?
Should we be integrating safety in all our machine automation?
Schneider Electric was one of the first to provide safety offerings for protecting press operators from serious accidents. Today, there is increasing demand to integrate safe automation in standard automation. Here is an abridged version in which they discuss the question.
Q. Let’s discuss the progressing integrating safety automation in standard automation.
A. I see strong markets for both stand-alone and embedded safety approaches. Some customers are looking for complete integration (combining safety and non-safety). They want shorter response times, simpler architecture, one system and software instead of two.
Many customers prefer to keep a separation between the safety and non-safety automation due to aspects around maintenance capabilities and independence from the supplier for non-safety aspects. With embedded safety offers, faster safety response times, one environment for all diagnostic information, common interfaces between technologies and 1/0 with a mixture of embedded safety.
Q. Where are some of the boundaries of these technologies?
A. Machine setup and maintenance are challenges. If safety modules are hardwired, it becomes too complicated to have multiple safety modules (functions) interacting. Integration can be expensive. Also, companies want maintenance personnel to be able to quickly change out a product without learning new software.
A popular solution for many customers is the range between safety modules and embedded safety controllers. Our modular safety controller you can put a CPU with two 1/0 expansion modules. The system can manage multiple functions and speed monitoring is simple to setup and manage over the life cycle of the machine.
Q. What are some of Schneider Electric’s main offerings in this arena?
A. Our core advantage is that we can supply our customers with the complete portfolio of devices to build their safety chain, such as sensor devices, pushbuttons (for emergency stop), HMI devices, contactors, drives, and safety processing devices (which consist of acquiring information devices, monitoring and processing devices, and stopping the machine devices).
Q. What type of functions are available to customers interested in safety controllers and embedded safety.
A. This is relatively new technology in the world of safety. Ten years ago, the philosophy was to stop the machine before doing anything with it. Now the goal is to slow it down to a safe speed or stop it momentarily and ramp up again as quickly as possible. As outlined in the C-type standard IEC 61800-5-2, there are multiple functions defined for safe motion that are intended to be used to improve the machinery’s usability:
– Safe Torque Off (STO) stop category 0 is typically used for most machines’ stop movement, which is a freewheeling stop. In motion-centric machines where freewheeling stop could end up with mechanical collision typically safe stop 1 or 2 is used as the deceleration ramp is monitored.
– Safe Stop 1 (SS1) stop category 1 is a monitored stop within a minimum time and ensures safety by continuously monitoring the deceleration ramp on the drive/motor. At the end of the ramp, where an equivalent zero speed is reached, the function is switched to STO.
– Safe Stop 2 (SS2) stop category 2 is a monitored stop within a minimum time and ensures safety by continuously monitoring the deceleration ramp on the drive/motor. At the end of the ramp, where an equivalent zero speed is reached, the function is switched to Safe Operating Stop (SOS), where continuous torque is applied to the motor and where movement is being monitored. If movement is detected, STO engages.
– Safe Limited Speed (SLS) monitoring is used to ensure the speed remains below a specific setting, very often used during maintenance operations.
– Safe Direction Indication (SDI) monitoring is often used in conjunction with SLS monitoring. For instance, we use an enabling switch handheld device to move specific motors at limited speed and direction on the machine. This is often used when loading of materials into the machine or jogging the machine to a specific position.
– Safe Maximum Speed (SMS) is used to limit the maximum speed of the machine. This function is often used to prevent an operator from changing the machine speed above the allowed maximum tolerable limits. There have been many cases where operators have entered an incorrect speed value within an HMI panel and the machine accelerated past its allowed limits and caused mechanical damages.
Go here for the original interview with Jason Minto, vice president of safety applications at Schneider Electric
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