Complementary Protective Measures

Can Emergency Stop be used as an “on/off” control?

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Emergency Stop Button
This entry is part 16 of 16 in the series Emer­gency Stop

Every couple of months I get an email ask­ing me if there is any reas­on why e-stop func­tions can’t be used as the primary power con­trol (on/off but­ton) for machinery. Fol­low­ing a recent exchange, I thought I would share the reas­ons for why this is such a bad idea. The short answer The short answer is an unequi­voc­al NO. Don’t […]

Complementary Protective Measures

Introduction to Functional Safety Seminars

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Man training a group of people, pointing to Functional Safety topics on the whiteboard

If you are inter­ested in func­tion­al safety, and I know many read­ers are based on the stat­ist­ics I see for my oth­er func­tion­al safety-related posts, I think you will be inter­ested in this. I am col­lab­or­at­ing with the IEEE Product Safety Engin­eer­ing Society’s Vir­tu­al Chapter to provide a series of three 35 minute sem­inars dis­cuss­ing the fun­da­ment­als of func­tion­al safety. The […]

Complementary Protective Measures

Emergency Stop Pull-Cords

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This entry is part 15 of 16 in the series Emer­gency Stop

This art­icle was updated 2019-04-26, adding spe­cif­ic details related to IEC 60947 – 5 – 5. When it comes to emer­gency stop devices there is no doubt that the red mush­­room-head push but­ton is the most com­mon – they seem to be every­where. The second most com­mon emer­gency stop device is the pull-cord, and like the light-cur­­tain in safe­guard­ing […]

Control Functions

Trapped Key Interlocking

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This is a trapped key interlock on the door of an electrical switchgear cabinet. To open the door the key must be inserted and turned to withdraw a bolt that holds the door closed. With the bolt withdrawn, the key is held in the lock. The upstream switching device is held open by another interlock using the same key; since the key can only be in one of the two locks, it prevents accidentally closing the upstream switch while the cabinet is open for maintenance. The interlock is attached to the door with one-way screws to discourage casual removal of the lock, which would defeat the system.
This entry is part 3 of 7 in the series Guards and Guard­ing

Many machine design­ers think of inter­locks as exclus­ively elec­tric­al devices; a switch is attached to a mov­able mech­an­ic­al guard, and the switch is con­nec­ted to the con­trol sys­tem. Trapped Key Inter­lock­ing is a way to inter­lock guards that is equally effect­ive, and often more appro­pri­ate in severe envir­on­ment­al con­di­tions. Copy­right secured by Digi­prove © 2018Acknow­ledge­ments: As cited.Some Rights ReservedOri­gin­al con­tent here is pub­lished under […]

Guards and Guarding

How to Apply a Safety Edge to a Machine Guard – Part 3: Stopping Performance

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CNC machine with sliding doors and safety edges
This entry is part 7 of 7 in the series Guards and Guard­ing

In Part 2 of this art­icle, I looked at the pres­sure-sens­it­ive devices (safety edges) them­selves. This part explores the stop­ping per­form­ance require­ments that engin­eers and tech­no­lo­gists need to con­sider when apply­ing these devices. Copy­right secured by Digi­prove © 2018Acknow­ledge­ments: As cited in the text.Some Rights ReservedOri­gin­al con­tent here is pub­lished under these license terms: X License Type:Non-com­mer­cial, Attri­bu­tion, Share AlikeLi­cense Sum­mary:You may copy this con­tent, […]

Guards and Guarding

How to Apply a Safety Edge to a Machine Guard – Part 2: Design Considerations

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CNC machine with sliding doors and safety edges
This entry is part 6 of 7 in the series Guards and Guard­ing

In Part 1 of this art­icle, I looked at the pres­sure-sens­it­ive devices (safety edges) them­selves. This part explores the design require­ments that engin­eers and tech­no­lo­gists need to con­sider when apply­ing these devices. Copy­right secured by Digi­prove © 2018Acknow­ledge­ments: As cited in the text.Some Rights ReservedOri­gin­al con­tent here is pub­lished under these license terms: X License Type:Non-com­mer­cial, Attri­bu­tion, Share AlikeLi­cense Sum­mary:You may copy this con­tent, cre­ate […]

Guards and Guarding

How to Apply a Safety Edge to a Machine Guard – Part 1: Pressure-sensitive devices

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CNC machine with sliding doors and safety edges
This entry is part 5 of 7 in the series Guards and Guard­ing

Safety Edges are often for­got­ten as safe­guard­ing devices. Most machinery engin­eers and design­ers are famil­i­ar with inter­lock­ing devices and light cur­tains, but once we step away from the famil­i­ar, our under­stand­ing of how to apply safe­guard­ing devices like a safety edge becomes a bit foggy.  Copy­right secured by Digi­prove © 2018Acknow­ledge­ments: SafeInd, IEC, ISO, Rock­well Auto­ma­tio more…Some Rights ReservedOri­gin­al con­tent here is pub­lished […]

Control Functions

Q & A: Category 2 and Testing Intervals

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Logical block diagram for ISO 13849-1 Category 2 architecture.
This entry is part 1 of 2 in the series Q&A

Dur­ing the Free Safety Talks that we did with Schmersal Canada and Frank­lin Empire, we had a “hot ques­tion” come up regard­ing Cat­egory 2 archi­tec­ture and the test­ing inter­val require­ment. In the short video below, Doug answers that ques­tion. If you have more ques­tions or felt some­thing wasn’t clear in the video, leave us a com­ment and […]

Events

Five reasons you should attend our Free Safety Talks

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Banner for the Free Safety Talks

Reas­on #1 – Free Safety Talks You can’t argue with Free Stuff! Last week we partnered with Schmersal Canada and Frank­lin Empire to put on three days of Free Safety Talks. We had full houses in all three loc­a­tions, Wind­sor, Lon­don and Cam­bridge, with nearly 60 people par­ti­cip­at­ing. We had two great presenters who helped […]

Canada

Safe Drive Control including Safe Torque Off (STO)

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Graph illustrating STO Function
This entry is part 12 of 16 in the series Emer­gency Stop

Ed. Note: This art­icle was revised 25-Jul-17 to include inform­a­tion on safe stand­still. Safe Drive Con­trol includ­ing STO Motor drives are every­where. From DC vari­able speed drives and index­ing drives, through AC Vari­able Fre­quency drives, servo drives and step­per motor drives, the cap­ab­il­it­ies and the flex­ib­il­ity of these elec­tron­ic sys­tems has giv­en machine design­ers unpre­ced­en­ted […]