I have a G120C drive that control position via analog encoder. I use S71500 with TIA Portal v16, communicate with drive via profinet and sina_speed (telegram1) in program. In this application need to stop the motor in position with stable stop positions.

  For example i want to move 500mm i start with 20Hz and at 400mm decrease the speed 5Hz and at 500mm send OFF1 to drive and some stop from 510mm to 580mm (80mm differential). In drive use dc brake for off1/off3 and try all parameters around this operation. I think is very unstable stopping position, i want more stable results with lower differential betwin stop positions for example 20 or 40mm differential and i don't care how far from set point. 

 Also i hear (the noise in motor when send dc the drive) a delay in dc brake when i disable the command of Sina_speed (so send off1 to drive). 

 The same application i used compact PID without brake and stop with +-1mm accuracy but this time i want lowest speed 5Hz for moving the motor and i can't use PID, i thought to use a PWM (like digital output) when a decrease the speed at least mm and i don't know how to do, for example i want a pid or something else that give only 0 or 100% output (that i will transform to 0-100% of setting speed this time). 

Hi,

maybe overthink your concept with speed control and braking ramps.

Here is an application for encoderless positioning with SIMATIC and SINAMICS G drives. This could be interesting for you:

https://support.industry.siemens.com/cs/de/en/view/109767951

 I tried encoderless position axis but i have the same problem because these objects are designed for servo motors, decrease also the speed to catch setpoint and my application can't working.

Why not use a Technology Object for positioning and let it handle the motor positioning command - instead of speed commands.  The drive would need to be set up for servo instead of vector control.

Bill_Raptakis

  I have a G120C drive that control position via analog encoder. I use S71500 with TIA Portal v16, communicate with drive via profinet and sina_speed (telegram1) in program. In this application need to stop the motor in position with stable stop positions.

  For example i want to move 500mm i start with 20Hz and at 400mm decrease the speed 5Hz and at 500mm send OFF1 to drive and some stop from 510mm to 580mm (80mm differential). In drive use dc brake for off1/off3 and try all parameters around this operation. I think is very unstable stopping position, i want more stable results with lower differential betwin stop positions for example 20 or 40mm differential and i don't care how far from set point. 

 Also i hear (the noise in motor when send dc the drive) a delay in dc brake when i disable the command of Sina_speed (so send off1 to drive). 

 The same application i used compact PID without brake and stop with +-1mm accuracy but this time i want lowest speed 5Hz for moving the motor and i can't use PID, i thought to use a PWM (like digital output) when a decrease the speed at least mm and i don't know how to do, for example i want a pid or something else that give only 0 or 100% output (that i will transform to 0-100% of setting speed this time). 

Sorry Einstein,

G120C does neither support a direct connection to a positioning Technology Object nor the internal basic positioner. 

As it has no encoder interface you cannot really do a good position control in my eyes. Just a very rough one with encoderless position control - there is the application that I linked before in the post. 

If you have requirements to position accuracy it is very counter productive to have no encoder and an asynchronous motor which works to the principle of having slip. 

I think you will maybe need an external encoder connected to the SIMATIC (e.g. PROFINET encoder) to do a real position control. I know this is not what you want to hear but I guess you already tried a lot to optimize your actual solution. 

@RB91, thanks for the info about the G120C.  When I was replying, I was simply looking at the topic title and the C was omitted.  That said, I did not know the C was not TO / servo DO capable either, so if the C had been in the topic title, I probably still would have said the wrong thing...... 

If I were responsible for a successful positioning on this system, I would strongly recommend upgrading the drive to a G120 with CU250E-2 PN or whichever G120 CU with an encoder interface, paired with a PM240-2, DC brake resistor, and then handle the positioning all in the PLC using that Technology Object (TO) and motion control there.  If the positioning was still too sloppy, update the PLC to low-end s7-1500 or S7-1510T strictly for motion control.

FYI, I do not work for Siemens directly or indirectly.  I am an end-user who does not know all the answers, but I think I have a decent feel for the range of capabilities.  If I do a one-off project, I might start with a more powerful PLC than I really think is required.  At the end of the project, I'll have learned how my assumptions and estimates worked out in the real project and real world.

My most recent high-end project started out as an s7-1517.  It is currently s7-1518.  I think I can probably go back to s7-1517 - except one requirement for high speed data capture and transfer to PC at 5000 Hz.  The s7-1517 could not hit 5000 Hz.  The s7-1518 does it with room to spare!

RB91

Sorry Einstein,

G120C does neither support a direct connection to a positioning Technology Object nor the internal basic positioner. 

As it has no encoder interface you cannot really do a good position control in my eyes. Just a very rough one with encoderless position control - there is the application that I linked before in the post. 

If you have requirements to position accuracy it is very counter productive to have no encoder and an asynchronous motor which works to the principle of having slip. 

I think you will maybe need an external encoder connected to the SIMATIC (e.g. PROFINET encoder) to do a real position control. I know this is not what you want to hear but I guess you already tried a lot to optimize your actual solution. 

How do you determine the position of the movement, do you have an encoder or something else?

How heavy is the product you are moving? What kind of ramps do you have? Do you have a braking resistor? (That's kind of mandatory if you want to have precise stopping with AC motor)

 Dear Einstein,

   Thanks for your answer, this time I use CPU s7-1511-1 PN. In the same machine I have one more complicated application with vertical movement,  gravity effect, 3000rpm Speed and I have perfect positioning (+-1mm) only with compact PID (only P control) without eneble dc brake, with the same drive. In application that I ask help I can't use PID because I need minimum speed. For this reason I use dc brake, I decrease the speed round to 60rpm and the motor stop position has accuracy +-8mm, when I increase the speed at 100-150rpm  i has accuracy +-75mm etc. 

0_Einstein

@RB91, thanks for the info about the G120C.  When I was replying, I was simply looking at the topic title and the C was omitted.  That said, I did not know the C was not TO / servo DO capable either, so if the C had been in the topic title, I probably still would have said the wrong thing...... 

If I were responsible for a successful positioning on this system, I would strongly recommend upgrading the drive to a G120 with CU250E-2 PN or whichever G120 CU with an encoder interface, paired with a PM240-2, DC brake resistor, and then handle the positioning all in the PLC using that Technology Object (TO) and motion control there.  If the positioning was still too sloppy, update the PLC to low-end s7-1500 or S7-1510T strictly for motion control.

FYI, I do not work for Siemens directly or indirectly.  I am an end-user who does not know all the answers, but I think I have a decent feel for the range of capabilities.  If I do a one-off project, I might start with a more powerful PLC than I really think is required.  At the end of the project, I'll have learned how my assumptions and estimates worked out in the real project and real world.

My most recent high-end project started out as an s7-1517.  It is currently s7-1518.  I think I can probably go back to s7-1517 - except one requirement for high speed data capture and transfer to PC at 5000 Hz.  The s7-1517 could not hit 5000 Hz.  The s7-1518 does it with room to spare!

RB91

Sorry Einstein,

G120C does neither support a direct connection to a positioning Technology Object nor the internal basic positioner. 

As it has no encoder interface you cannot really do a good position control in my eyes. Just a very rough one with encoderless position control - there is the application that I linked before in the post. 

If you have requirements to position accuracy it is very counter productive to have no encoder and an asynchronous motor which works to the principle of having slip. 

I think you will maybe need an external encoder connected to the SIMATIC (e.g. PROFINET encoder) to do a real position control. I know this is not what you want to hear but I guess you already tried a lot to optimize your actual solution. 

 

 Dear Hati, 

   I have an analog encoder. I move a 8 pistons with water inside, it's not heavy but I haven't good flow in my system when I decrease the speed under 60rpm. I didn't use resistor because Siemens tell me that is not necessary if drive didn't stop with dc link fault.  My motor has rated current 6.45A and I tried dc brake current from 3 to 12A without change something.

Hati

How do you determine the position of the movement, do you have an encoder or something else?

How heavy is the product you are moving? What kind of ramps do you have? Do you have a braking resistor? (That's kind of mandatory if you want to have precise stopping with AC motor)