matching motor speed using d/a converter

Currently doing a project for a ship canopy. I am using a mitsubishi fx 1s plc. The canopy is wrapped around a drum, when the drum motor is activated(forwards) the canopy comes out,and comes back in when put in reverse.There is also a 'screw jack' motor which operates guides either side of the canopy. These guides obviously need to run at the same speed as what the canopy is going out or coming in.the drum motor runs at a constant speed of 12rpm and a pulse senseor is used as an input to the plc for the speed 'measurement'. There will be 18 pulses per revolution.(The screw jack motor is run via an inverter which is run via a D/A converter on the plc.)The problem is matching the speed of the canopy guides to the speed of which the canopy is coming out or going back in at.Bearing in mind that as it comes out it will do so slower the further it gets out as it is unravelling off the drum therefore decreasing the canopy drum diameter.Similarly as the canopy is brought back in it will speed up slighlty due to an increase in this diameter.I am struggling very much with this part of the program.

From your discription the drum turns at a constant RPM but the linear speed varies. Your analog out will be porportional to how much is spooled out or in. It seems like you could adjust your analog up or down as you spool out. In other words as you count pulses out for each logical set lower your output speed one unit etc.

Does this make any sense?

John Thornton

BTW, I don't run into many Thornton's...

motor speed matching using d/a converter

Thanks for your reply,
What you suggested makes sense. I understand that i need to increment and decrement the analogue output but I do not know when to do this.i.e after each rotation of the drum or after each pulse of the sensor.

Thanks again,
Nathan Thornton

That just depends on your exact ratios so you would have to do the math on that to see when it is best to adjust the speed reference. I would guess that for each pulse you would change the speed for smoothest operation.

John

How about running the guide motors in speed control and the canopy in torque control. The torque will be set to overcome friction and generate an aceptable tension in the canopy. What change in diameter do you get from the canopy being fully open to fully closed ?

RE matching motor speed using d/a converter

Currently doing a project for a ship canopy. I am using a mitsubishi fx 1s plc. The canopy is wrapped around a drum, when the drum motor is activated(forwards) the canopy comes out,and comes back in when put in reverse.There is also a 'screw jack' motor which operates guides either side of the canopy. These guides obviously need to run at the same speed as what the canopy is going out or coming in.the drum motor runs at a constant speed of 12rpm and a pulse senseor is used as an input to the plc for the speed 'measurement'. There will be 18 pulses per revolution.(The screw jack motor is run via an inverter which is run via a D/A converter on the plc.)The problem is matching the speed of the canopy guides to the speed of which the canopy is coming out or going back in at.Bearing in mind that as it comes out it will do so slower the further it gets out as it is unravelling off the drum therefore decreasing the canopy drum diameter.Similarly as the canopy is brought back in it will speed up slighlty due to an increase in this diameter.I am struggling very much with this part of the program.



Nathan



Build a Hash Table



Build a table with two pockets. You send the Hash table an index value and you get a value back.

In your case the Hash Index will be the pulse count of the drum sensor. Seup a high-speed counter on the drum sensor and reset the counter each time the Canopy is retracted




The Hash value will be the speed value.

You can put as many lines in the hash table you want. The more lines the more different speed settings. I think you may only need three lines a startup speed a run speed and a slow/stop speed. But that will depend on your hardware.




As the drum count changes it keeps pulling up different speeds from the hash table. You can hard code the Hash table values.

Best Regards


Doug Hylton