machinery Safety
Here is an explanation I have sent to management recently about machinery safety. This is for a compression moulding machine large enough for the operator to get their upper body inside. Of course the regulations only apply in Europe.
The safety circuit is divided into 2 parts;
1. Emergency stop.
2. Safety gate.
1. The emergency stop consists of 2 E-stop pushbuttons, these are latching on, twist to release. These e-stops are monitored by a PIlz PNOZ16S safety relay. If either stop is operated the the relay de-energisies and disconnects the control circuits to the gate safety circuit. The relay has a seperate "reset" button that energises the Pilz relay after releasing the emergency stop pushbutton. This ensures that the requirements of BSEN 954 and BSEN 60204 are met in that the re-setting of an emergency stop push does not initiate a movement. Using a PNOZ16S and 2 channel e-stops means that the e-stop system is category 4, this is the category required for safety sytems for presses as a fault could result in serious injury or death.
2. The gate safety circuit is also a PNOZ16S safety relay, in this case the pilz relay monitors 2 ferrocode coded magnetic switches that are fitted to the operators gate. when the gate is opened the Pilz relay is de-energised and opens the 2 MPCE contactors that isolate the variable speed drive output from the motor, these contactors are also monitored by the pilz relay so that if either of them fails to open when de-energised then the pilz relay will not reset. Also in the gate circuit are trojan 5 tongue operated interlock switches that are fitted to the rear guards. If one of the guards is opened then the gate safety pilz relay de-energises. The Pilz relay is wired with a reset pushbutton so that when the gate is closed the operator has to push the reset button to energise the pilz relay. This ensures that closing the gate does not initiate any movement and prevents an operator from entering the danger area and closing the gate behind him. This is also category 4.
The safety contacts of the E-stop relay and the gate relay are in series.
More information can be found here : http://www.pilzsupport.co.uk/downloads_gms.htm
the new European standard for machinery safety is BSEN 12100 Safety of Machinery - Basic concepts, general principle for design.
http://www.pilzsupport.co.uk/standards/safety.htm has a list of all the myriad relevant standards.
The underlying principles of the system we have are;
1. A category 4 safety system - from BSEN 954-1 " ......A further requirment of category 4 is that a single fault in any safety-related parts of the system shall not cause the loss of the safety function. The single fault must be detected at or before the next demand upon the safety system. If this is not possible, an accumulation of faults shall not lead to the loss of the safety function...."
2. Preventing unexpected start up - from BSEN 60204-1 para 9.3.1 " The reclosing or resetting of an interlocking safeguard shall not initiate machine motion or operation where that can result in a hazardous condition"
Here is an explanation I have sent to management recently about machinery safety. This is for a compression moulding machine large enough for the operator to get their upper body inside. Of course the regulations only apply in Europe.
The safety circuit is divided into 2 parts;
1. Emergency stop.
2. Safety gate.
1. The emergency stop consists of 2 E-stop pushbuttons, these are latching on, twist to release. These e-stops are monitored by a PIlz PNOZ16S safety relay. If either stop is operated the the relay de-energisies and disconnects the control circuits to the gate safety circuit. The relay has a seperate "reset" button that energises the Pilz relay after releasing the emergency stop pushbutton. This ensures that the requirements of BSEN 954 and BSEN 60204 are met in that the re-setting of an emergency stop push does not initiate a movement. Using a PNOZ16S and 2 channel e-stops means that the e-stop system is category 4, this is the category required for safety sytems for presses as a fault could result in serious injury or death.
2. The gate safety circuit is also a PNOZ16S safety relay, in this case the pilz relay monitors 2 ferrocode coded magnetic switches that are fitted to the operators gate. when the gate is opened the Pilz relay is de-energised and opens the 2 MPCE contactors that isolate the variable speed drive output from the motor, these contactors are also monitored by the pilz relay so that if either of them fails to open when de-energised then the pilz relay will not reset. Also in the gate circuit are trojan 5 tongue operated interlock switches that are fitted to the rear guards. If one of the guards is opened then the gate safety pilz relay de-energises. The Pilz relay is wired with a reset pushbutton so that when the gate is closed the operator has to push the reset button to energise the pilz relay. This ensures that closing the gate does not initiate any movement and prevents an operator from entering the danger area and closing the gate behind him. This is also category 4.
The safety contacts of the E-stop relay and the gate relay are in series.
More information can be found here : http://www.pilzsupport.co.uk/downloads_gms.htm
the new European standard for machinery safety is BSEN 12100 Safety of Machinery - Basic concepts, general principle for design.
http://www.pilzsupport.co.uk/standards/safety.htm has a list of all the myriad relevant standards.
The underlying principles of the system we have are;
1. A category 4 safety system - from BSEN 954-1 " ......A further requirment of category 4 is that a single fault in any safety-related parts of the system shall not cause the loss of the safety function. The single fault must be detected at or before the next demand upon the safety system. If this is not possible, an accumulation of faults shall not lead to the loss of the safety function...."
2. Preventing unexpected start up - from BSEN 60204-1 para 9.3.1 " The reclosing or resetting of an interlocking safeguard shall not initiate machine motion or operation where that can result in a hazardous condition"
