Consider using an absolute encoder. If you lose power you do not lose position. Device Net would be a good choice with a Pepperl and Fuchs absolute multi turn encoder. Have used this combination before into an Omron CS1 PLC. Worked really well.
Encoder
- Thread starter Agostinho Macedo
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Agostinho Macedo
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encoders
Kalle, I appreciate very mutch your answer.
Why detector swichs have to be on elevator. I thinq I can do on reverse, with the detector´s fix on the struture and the metal on the elevator.
Another question I had thinq is about the minimum number of detectors swichs. If it is a vertical conveyor with 10 floor, then usually we need 10 + 2 detector´s , one for each floor and two for emergency. But in fact, I thinq it´s possible to do that with only 4 detector´s. Two for emergency stops just above floor 1 and 10, and only one to stop in each floor. Ok , you say to me , "How will you diferentiate eache floor ?" Well, I if the plc has memorize the destany floor and counts the number of changes made by the detector then the system will know where it has to stop ! I must remember here that the conveyor usually works in sequence (1,2,3,4,5,6,7,8,9,10). The other detector I´ll use attach to one "carreto" that is mounted on the motor, and will count the number of changes like one encoder. The precision give by this solution on this elevator is 1,3 mm, wich I thinq is enougth to control the up and down ramps.
My only doubt in this solution is to find a trigger function to interrupt plc scan. As I say before is my first time with encoders and I never use interrupt or trigger functions before. I work with momentum modicon plc wich have a minimum of 5,5 ms of input change ON/OFF/ON , and the total scan is 200 ms or even more.
PS - If fails the current, the position of the elevator will be memorize on a holding (4..... on momentum) register. In this case maybe I will need another detector to let the system know where is the elevator, or maybe I can use one of the emergency stop detector to do that.
Thanq you for all answers.
Kalle, I appreciate very mutch your answer.
Why detector swichs have to be on elevator. I thinq I can do on reverse, with the detector´s fix on the struture and the metal on the elevator.
Another question I had thinq is about the minimum number of detectors swichs. If it is a vertical conveyor with 10 floor, then usually we need 10 + 2 detector´s , one for each floor and two for emergency. But in fact, I thinq it´s possible to do that with only 4 detector´s. Two for emergency stops just above floor 1 and 10, and only one to stop in each floor. Ok , you say to me , "How will you diferentiate eache floor ?" Well, I if the plc has memorize the destany floor and counts the number of changes made by the detector then the system will know where it has to stop ! I must remember here that the conveyor usually works in sequence (1,2,3,4,5,6,7,8,9,10). The other detector I´ll use attach to one "carreto" that is mounted on the motor, and will count the number of changes like one encoder. The precision give by this solution on this elevator is 1,3 mm, wich I thinq is enougth to control the up and down ramps.
My only doubt in this solution is to find a trigger function to interrupt plc scan. As I say before is my first time with encoders and I never use interrupt or trigger functions before. I work with momentum modicon plc wich have a minimum of 5,5 ms of input change ON/OFF/ON , and the total scan is 200 ms or even more.
PS - If fails the current, the position of the elevator will be memorize on a holding (4..... on momentum) register. In this case maybe I will need another detector to let the system know where is the elevator, or maybe I can use one of the emergency stop detector to do that.
Thanq you for all answers.
Reconsider a device net absolute encoder. If you are worried about PLC scan times, input delays and interrupts, seriously have a long look at the new Omron CJ1 PLC. It is very fast, economical, has a Device Net master available and input filter times can be adjusted for the input card. Interrupts are easy to programme. Normal minimum input filter is, I think, 0.5 ms. I used one recently with approx 25kbytes of programme and the scan time was less than 3 ms.
Weather or not you use switches encoders or absolute encoders
my post was initiatly pointing out that 1000 p/r encoder may produce to many pulses for the input card to handle if the speed is too fast.
As far as the safety points are concerned i'm sure that would be integrated into the total system.
An encoder could be used easilly.
The safety system should be designed on the probable missing of counts or the failure of the encoder.
How far do you want your elevator to fall or go up if it doesn't know where it is.
My belief is that 1000 p/r is too fast - but I don't know your system.
my post was initiatly pointing out that 1000 p/r encoder may produce to many pulses for the input card to handle if the speed is too fast.
As far as the safety points are concerned i'm sure that would be integrated into the total system.
An encoder could be used easilly.
The safety system should be designed on the probable missing of counts or the failure of the encoder.
How far do you want your elevator to fall or go up if it doesn't know where it is.
My belief is that 1000 p/r is too fast - but I don't know your system.
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