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Entry type: FAQ Entry ID: 109779993, Entry date: 08/24/2020

SIMATIC MICRO-DRIVE: Positioning accuracy and position resolution of a Motion Control application with SIMATIC S7-1200/S7-1500.

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Calculation of the positioning accuracy and position resolution of a Motion Control application with the SIMATIC MICRO-DRIVE drive system and SIMATIC S7-1200/1500

With the Excel tool provided in this article you have the possibility of calculating the positioning accuracy for your individual mechanical system (motor/gearbox combination). The tool also supports you in determining the position resolution of your Motion Control application.

Positioning accuracy

The achievable positioning accuracy of a Motion Control application depends on the tolerances of the mechanical system used. These include, for example, the circumferential backlash of gearbox and clutch or the cogging torques of the motor. The resolution of the encoder used has an additional influence on the achievable positioning accuracy of the application, so this must be taken into account. In general, a gear or a transmission ratio contributes to increasing the attainable positioning accuracy, since the number of encoder steps per load revolution increases linearly with increasing transmission ratio.

You can combine the SIMATIC MICRO-DRIVE drive system with your individual motor system or with motors and plug-in connector cables from selected product partners. The product partner portfolio offers different gears for the respective motor sizes.

Example for positioning accuracy

In this example we determine the positioning accuracy for the ebmpapst geared motor "SGE63.20 DK1PP63100960" from the Siemens product partner program with IQ encoder and Performax®Plus 63.1 gearhead with a transmission ratio of i = 9. The IQ encoder, together with the evaluation electronics, provides a resolution of 400 sections (encoder line number/increments p0408 = 100). This results in a mechanical resolution of 3600 sections per load revolution at the gear output shaft. With a load movement of 1cm per revolution the encoder delivers an accuracy of 3µm. The Performax®Plus 63.1 gearhead has a typical circumferential backlash of approx. 1°. This results in a positioning accuracy of about 6µm for the gear motor.

Positioning with technology object

When positioning with the technology objects “TO_PositioningAxis” or “TO_SynchronousAxis”, a readjustment effect when reaching the target window might occur corresponding to the positioning accuracy. The readjustment of the technology object in the target window can be reduced or completely eliminated by increasing the permitted deviation. For this you can set the value <TO>.PositionControl.ControlDifferenceQuantization.Value according to the calculated positioning accuracy.

Position resolution

Use the Excel tool from this entry when configuring your application to determine the position resolution depending on the cycle time of the Motion Control processing of the CPU. This corresponds to the interpolator cycle and position controller cycle. The position resolution indicates the distance traveled by the load between two Motion Control cycles. Among other things, this is relevant for the response time, in case of strong fluctuations of the load profile during the motion cycle or when changing the Motion Control job.

Example for position resolution

Based on the example of positioning accuracy, the position resolution is now to be determined using the same motor system with different Motion Control cycle times. For this the load is positioned at a velocity of 130 mm/s. Depending on the Motion Control cycle time, there are different position resolutions and demands on the system performance of the controller. More information about the cycle time is available in Entry 59193558

Motion Control cycle Position resolution Performance requirements 
1 ms0.13 mm+ + + + 
4 ms0.52 mm+ + +
10 ms1.30 mm+ +
20 ms2.60 mm+
50 ms6.49 mm+

The SIMATIC S7-1200 Basic controllers are suitable for small to medium performance requirements. Use the SIMATIC S7-1500(T) Advanced controllers for advanced Motion Control applications.

Use the results as a basis for fast and convenient device selection and configuration with the TIA Selection Tool, see 109767888.

The load speed and the Motion Control cycle time have a significant influence on the synchronization behavior of axes. In contrast, the influence on the performance of the positioning is significantly lower.

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