## Topic:

- What is the meaning and scaling of EPOS4's resp. IDX's object "Torque actual value"?
- How is the value of the object "Torque actual value" evaluated?

## Solution:

### 1.) Scaling of "Torque actual value"

The value of the object **"Torque actual value" (0x6077)** and **"Torque actual averaged" (0x30D2-01)** is given in **[per mill]** (= 1/1000) resp. displayed in [%] by EPOS Studio's "Data recorder" and **refer to the "Motor rated torque" (0x6076)** in [μNm], i.e. the motor's "Nominal torque" (specified in [mNm]).

Please find more details in the "**EPOS4 Firmware Specification**" too:

### 2.) "Motor rated torque" evaluation

The **"Motor rated torque" (0x6076)** is calculated by the EPOS4 resp. IDX by a **multiplication of the motor's "Nominal current" (0x3001-01) and its "Torque constant" (0x3001-05). **These both base motor data values have to be configured by EPOS Studio's "Startup" wizard during initial commissioning based on the motor's data sheet.

Example: "EC-i 40", PN: 496651

The value of the object **"Torque constant" (0x3001-05)** can be **configured manually by the "Startup" wizard** (based on the motor's data sheet)** or it can be identified automatically during "Regulation Tuning"**.

**Important:**

The value of the **"Nominal current"** and the **"Torque constant" have to be configured properly**. Otherwise the internally calculated "Motor rated torque" (0x6076) will be wrong and the reported "Torque values" might be misleading.

### 3.) Torque value calculation

Please note that there is **no torque measuring device present to measure the motor torque!** **Any object with a torque value just provides a calculated value. **The calculation is based on the measured **"Current actual value" (0x30D1-02) multiplied with the "Torque constant" (0x3001-05) **which was configured or evaluated during tuning.

**The [per mill] value of the "Torque actual value" (0x6077)** is based on the following formula:

- "Torque actual value" [per mill] = ("Current actual value" [mA] / "Nominal current" [mA]) * 1000

The **torque [mNm]** can be calculated based on the reported [per mill] value of the "Torque actual value" (0x6077) by one of the following formulas:

- Torque [mNm] = ("Torque actual value" [per mill] / 1000) * ("Motor rated torque" [μNm] / 1000)
- Torque [mNm] = ("Torque actual value" [per mill] / 1000) * "Motor rated torque" [mNm]
- Torque [mNm] = ("Torque actual value" [per mill] / 1000) * ("Nominal current" [mA] / 1000) * ("Torque constant" [μNm/A] / 1000)
- Torque [mNm] = ("Torque actual value" [per mill] / 1000) * "Nominal current" [mA] / 1000) * "Torque constant" [mNm/A]
- Torque [mNm] = ("Torque actual value" [per mill] / 1000) * "Nominal current" [A] * "Torque constant" [mNm/A]

### 4.) Torque accuracy?

Due to the fact that the reported torque values by the controller are just calculated based on motor current, these will **not(!) correspond precisely to a torque measured by an output shaft torque sensor**. There are different possible root causes for such a discrepancy:

- There are a lot of
**"constants"**part of the internal torque calculation which**have to be configured properly**but still have a**tolerance of +/-10%**typically. **Motor winding temperature**will also have some slight influence on the "constants".- If a
**gear**is present, its**efficiency**(at the actual working point) can have a remarkable impact on the reported torque compared to the output shaft torque measured dynamically by a torque sensor.

## Final conclusion:

- The reported
**"Torque values" reported by the EPOS4 or IDX are [per mill] (= 1/1000) of the "Motor rated torque" (0x6076)**resp. motor's nominal torque. - The
**"Torque values" are just internally calculated values**based on the motor current measurement and motor constants. These derived torque values are**not(!) highly accurate**. - If a
**precise output shaft torque data**(esp. of a gear's output shaft torque) is required,**a torque meter or torque sensor will be required**which can measure the torque dynamically during motion.

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