Editing Configuring cogging torque compensation
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| − | + | [https://en.wikipedia.org/wiki/Cogging_torque Cogging torque] compensation feature in drive that aims to make motor torque production more uniform and ideal. | |
''"Cogging torque of electrical motors is the torque due to the interaction between the permanent magnets of the rotor and the stator slots of a Permanent Magnet (PM) machine. It is also known as detent or ‘no-current’ torque. This torque is position dependent and its periodicity per revolution depends on the number of magnetic poles and the number of teeth on the stator.”'' | ''"Cogging torque of electrical motors is the torque due to the interaction between the permanent magnets of the rotor and the stator slots of a Permanent Magnet (PM) machine. It is also known as detent or ‘no-current’ torque. This torque is position dependent and its periodicity per revolution depends on the number of magnetic poles and the number of teeth on the stator.”'' | ||
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This can be compensated by modulating motor current to counter the motor cogging. In some Granite Devices drives ([[IONI]] Pro family on the time of writing) there are options to adjust compensation current by few parameters. | This can be compensated by modulating motor current to counter the motor cogging. In some Granite Devices drives ([[IONI]] Pro family on the time of writing) there are options to adjust compensation current by few parameters. | ||
| + | {{picturebox|torqueCompensation.png|596px|caption=Cogging torque compensation parameters in Granity}} | ||
==Configuration== | ==Configuration== | ||
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===Parameters=== | ===Parameters=== | ||
Static no-current cogging compensation is done by summing a fixed amplitude waveform on the torque [[setpoint]]. The default waveforms are sinusoidal where phase angle of sine is driven by motor angle. | Static no-current cogging compensation is done by summing a fixed amplitude waveform on the torque [[setpoint]]. The default waveforms are sinusoidal where phase angle of sine is driven by motor angle. | ||
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Determining cogging torque frequency is straight forward. | Determining cogging torque frequency is straight forward. | ||
#Rotate unpowered motor by hand count the number of major "steps" or "cogs" per revolution | #Rotate unpowered motor by hand count the number of major "steps" or "cogs" per revolution | ||
| − | #Divide this number by motor poles and multiply by two. So equation is N=2*number_of_cogs/pole_count (same as {{param|MPC}}. | + | #Divide this number by motor poles and multiply by two. So equation is N=2*number_of_cogs/pole_count (same as {{param|MPC}}. |
| − | #The optimal TRF1 function is either Sin(Nx) or Cos(Nx). | + | #The optimal TRF1 function is either Sin(Nx) or Cos(Nx). |
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{{warning|These methods are done on user's own risk. Remember that any malfunction in software or hardware may cause unexpectedly high torque.}} | {{warning|These methods are done on user's own risk. Remember that any malfunction in software or hardware may cause unexpectedly high torque.}} | ||
As the frequency is known, we proceed choosing the correct function and amplitude setting: | As the frequency is known, we proceed choosing the correct function and amplitude setting: | ||
#Set drive in torque mode and enable it without any setpoint | #Set drive in torque mode and enable it without any setpoint | ||
| − | #Start with Sin(Nx) function and try different | + | #Start with Sin(Nx) function and try different TRA2 values (positive and negative, varying magnitudes). On each TRA2 value, try rotating motor by hand and identify the lowest cogging setting. |
#Repeat the last step but this time with Cos(Nx) function. | #Repeat the last step but this time with Cos(Nx) function. | ||
#Choose the settings that yielded the lowest cogging | #Choose the settings that yielded the lowest cogging | ||
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Perform the above procedure first for cogging torque, and then for ripple if necessary. However, in the ripple settings (TRF2 and TRA2), the test & comparison should be conducted when torque setpoint is set to a constant non-zero value (i.e. using {{param|TSP1}} and Set Abs button. In this case, motor should be held still and rotated by hand to determine the lowest ripple settings. | Perform the above procedure first for cogging torque, and then for ripple if necessary. However, in the ripple settings (TRF2 and TRA2), the test & comparison should be conducted when torque setpoint is set to a constant non-zero value (i.e. using {{param|TSP1}} and Set Abs button. In this case, motor should be held still and rotated by hand to determine the lowest ripple settings. | ||
{{machine|Beware of handling motor when torque setpoint is given. Always start with very low setpoint values to avoid injury or damage. Always keep emergency stopping method rapidly accessible.}} | {{machine|Beware of handling motor when torque setpoint is given. Always start with very low setpoint values to avoid injury or damage. Always keep emergency stopping method rapidly accessible.}} | ||
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