EV Motor Shaft Angle Sensing and Measurements

Introduction

Rotation sensors measure the rotational speed and angle of spinning objects, making them useful across various industries. In the automotive sector, these sensors monitor the rotational speed and angle of the rotating axle. For electric vehicle (EV) motors, this data is used to maximize the control and performance of a vehicle. They also integrate with steering operations to enhance vehicle stability, contributing to safety and performance.

Beyond automotive applications, rotation sensors are used in controlling and monitoring rotational equipment across different transportation modes, including aircraft, ships, and railway vehicles. In industrial settings, they ensure the stable operation of turbines, conveyor belts, and other rotating machinery by providing real-time feedback to control systems.
In the medical field, rotation sensors enable precise motion control in surgical robots, while in home appliances, they optimize the performance of devices like washing machines and refrigerators. The versatility of rotation sensors underscores their importance in advancing technology and ensuring the efficient operation of various systems.

Challenges

Rotation angle sensors come in various forms, including encoders, resolvers, and Hall sensors. The choice of sensor depends on factors such as cost, performance, size, and the operating environment. However, because rotation sensors do not directly output angle measurements, additional components such as counters, converters, or similar devices are required to convert the raw data into angular position. When evaluating the performance of products that use rotating components, such as motors, it’s often necessary to measure and verify the rotation angle alongside control signals and other physical parameters, such as torque and vibration. This can be challenging, as it may require separate instruments for each sensor type, leading to increased complexity and analysis time. Moreover, when using a signal conditioner to convert the sensor signal into rotational angle, time skew can lead to discrepancies between the rotation angle and other signals, compromising the accuracy of the evaluation.

Solutions with the DL950

• Encoder Rotation Angle Measurement
• Hall Sensor Rotation Angle Measurement
• Resolver Rotation Angle Measurement
• Synchronized Measurement of Various Signals

Explanations of Solutions with the DL950

Encoder Rotation Angle Measurement

Encoders are classified into two main types: incremental encoders, which detect relative angles, and absolute encoders, which detect absolute angles.
Incremental Encoders :
Incremental encoders vary in the number of output signals they generate. Common configurations include single-phase (A-phase), two-phase (A-phase and B-phase), and threephase (A-phase, B-phase, and Z-phase). The DL950 can compute the rotation angle for all these configurations. All outputs from incremental encoders are pulse waves, with the number of pulses per rotation specified by the encoder manufacturer. The A and B outputs are phase shifted, allowing for determination of rotation direction. The Z-phase generates a single pulse per rotation, serving as a reference position. The DL950 can capture the voltage signals and display concurrently with the decoded rotation angle in real-time.
Absolute Encoders :
Absolute encoders use a disk with multiple rows of slits that output all rows as a binary number or Gray code. The DL950 supports absolute encoders up to 16 bits, with the parallel signals from the encoder fed into the DL950’s logic module, allowing real-time display of the rotation angle as a waveform.

Figure 2. Example of computed encoder angle measurement

Figure 3. Example of encoder rotation angle computation measurement

Hall Sensor Rotation Angle Measurement

A Hall sensor converts changes of the rotating magnetic field into an electrical signal using the galvanomagnetic effect (Hall effect). When the magnetic field changes with each pole during the rotation of a motor, the Hall sensor outputs a pulse wave. By inputting this signal into the DL950, these pulses can be converted and displayed as the rotational angle (electrical angle) in real-time.

Figure 4. Hall sensor output signal

Figure 5. Example of Hall sensor rotation angle computation measurement

Resolver Rotation Angle Measurement

A resolver is a rotational position sensor that outputs two signals based on sinθ and cosθ from detection coils, which correspond to the rotor’s angle when an excitation signal is applied. The rotor angle is detected by measuring the phase shift in the voltage output from the two-phase rotor coil as it rotates. These signals (sinθ, cosθ) are modulated by the excitation signal, forming a carrier wave that represents the rotor’s position, as illustrated in Figure 5.

Typically, a resolver-to-digital (RD) converter is needed to compute the rotation angle. However, using the DL950’s built-in resolver calculation function, the rotation angle can be displayed as a real-time waveform by analyzing the excitation, sin, and cos signals directly. The DL950 also allows for adjustments based on resolvers with axis double angle, enabling precise rotation angle computation that accounts for this parameter.

Figure 6. Resolver Output Signal

Figure 7. Example of Resolver Rotation Angle Calculation

Synchronized Measurement of Various Signals

In motor and inverter testing, it’s important to measure not only motor position but also parameters like output voltage, current, temperature, and vibration from the inverter. Capturing these values synchronously allows for a correlation to be made between these parameters and rotor position. The DL950’s real-time math function enables the decoding and real-time trending of rotation sensor signals. By processing data in real time, it displays results alongside the input signals, making it easier to analyze correlations between motor signals and position. With the capability to perform up to 16 simultaneous computations, the DL950 supports not only rotation angle calculations but also other critical computations during testing.

Figure 8. Example of Encoder Rotation Angle