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Entry type: FAQ Entry ID: 48203982, Entry date: 02/24/2011
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How must you parameterize the IM 174 in combination with the Technology CPU or SIMOTION when steppers are to be addressed without encoder feedback?

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Description
Below are instructions on how to parameterize the IM 174 with Technology CPU or SIMOTION to be able to use a stepper drive without encoder feedback.
In this FAQ we take the example of a stepper motor with the data below.
 

Max. torque Mm [Ncm] 1500
Holding torque MH [Ncm] 1695
Rotor moment of inertia JR [kgcm²] 16
Step number z [1/U] 1000
Step angle a[°] 0,36
Nominal current/cable Iw [A ] 4,75
Resistance/winding Rw [Ώ] 1,9
Current rise time constant t [ms] 22
Weight (approx.) G [kg] 11
Motor voltage U [V] 325
Table 1: Technical data of the sample stepper motor


Fig. 01: Characteristics of the sample stepper motor

Key:

  1. Characteristic of maximum torque at maximum slew stepping rate
  2. Start-stop characteristic (starting frequency depending on the load torque)
  3. Characteristic of load moment of inertia

Step 1: Interpret the data sheet of the stepper motor
A minimum torque is technologically required based on the application/mechanics. Taking this required minimum torque and the stepper motor characteristic you can determine the maximum frequency at which this stepper motor is allowed to be addressed to still achieve the required torque.
In this example we assume that the application requires a minimum torque of 10Nm. The stepper motor used in this example has a maximum permitted torque of 15 Nm, so it is suitable for our purposes. The stepper motor has 1000 steps per revolution (z). To determine the maximum permissible frequency (fmax) you draw a horizontal line at 10 Nm and determine the frequency or speed matching the torque at the intersection with Curve 1. In this case 10Nm corresponds to fmax=9000Hz.
The normalizing frequency (fNorm) is determined in the same way (maximum torque 15Nm corresponds to 4500Hz rounded up to 5000Hz): fNorm= 5000Hz


Fig. 02: Determining the maximum frequency

Step 2: Make settings in the hardware configuration
You must make the settings below for the stepper motor described above when parameterizing the IM174 in the hardware configuration.
 

Parameter Value Description
Drive type "Stepper" Selection of drive type: stepper motor
Max.freq.[Hz] 9000 Maximum permitted frequency fmax of the step motor
determined from the data sheet of the stepper motor
Norm.freq.[Hz] 5000 Normalization frequency fNorm of the step motor
determined from the data sheet of the stepper motor
Encoder type "Stepper" Selection of the encoder type: stepper motor
Reserved bits for fine resolution 0 Fine resolution
Table 2: Hardware configuration (HW Config) of the IM174


Fig. 03: Hardware configuration (HW Config) of the IM174

Step 3: Calculate the maximum motor speed
The maximum step frequency has been determined from the characteristic; using the formula n=1/z*fs (z=step number, fs=step frequency) you get the maximum speed of
nmax =  1/1000 * 9000 Hz  =  9 U/s  = 540 U/min

Step 4: Calculate the normalization motor speed (normalization speed)
The normalization step frequency of 5000Hz has been determined from the characteristic; using the formula n=1/z*fs (z=step number, fs=step frequency) you get the normalization speed of:
nNorm = 1/1000 * 5000 Hz = 5 U/s = 300 U/min

Step 5: Make settings in S7 Technology
You must make the settings below in S7T Config / SIMOTION Scout.
 

Settings in the axis configuration
Parameter Value Description
Maximum motor speed [rpm]
540 Here you enter the speed nmax calculated in Step 3.
Encoder pulse per revolution 1000 Steps per revolution (= step number)
Fine resolution 1 "1" must always be entered for stepper motors.
Settings in the expert list of the TO "Axis"
(Right-click > Expert > Expert List > Configuration Data)


Fig. 04

Parameter Value Description
SetPointDriverInfo.
DriveData.
maxSpeed
540 Check that the maximum speed nmax calculated in Step 3 is entered here.
SetPointDriverInfo.
DriveData.
nominalSpeed
300 Here you enter the normalization speed nNorm calculated in Step 4.
SetPointDriverInfo.
DriveData.
speedReference
[1] nominal_value  
Table 3: Parameters of the Technology Object (TO) "Axis" in S7 Technology or SIMOTION Scout

Step 6: Switch off control to check normalization
As long as the position controller is active it also corrects deviations arising from incorrect programming. To check the parameterization you must therefore deactivate the position controller and do a controlled positioning of the axis.
In order to do a controlled positioning of the technology object (TO) Axis you set the position control loop amplification to 0.0 1/s in the axis parameterization (static controller data) in S7T Config/SIMOTION Scout and activate speed pre-control with a weighting factor of 100%.


Fig. 05: Switching of the controller to prepare for normalization check

Step 7: Check normalization
To check that the normalization is correct the axis is controlled to travel a defined path. If the axis does not reach the target coordinates and there is no step loss, the normalization is incorrect and must be corrected.

Step 8: Optimize the position controller
Now you must reactivate and optimize the position controller of the axis. For this please follow the instructions (also for the control loop amplification and pre-control) in the S7 Technology manual in Entry ID 30119663, section 8.4.

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