Testing and Validation of Small Electric Motors Using an Efficient Test Bench Design

As we developed our test bench at LOGICDATA, we faced a specific challenge: managing multiple drive components efficiently

says Mechanical Expert Andreas Pichler, responsible for the test bench design. 

Our goal was to create a setup that allowed for a simple and rapid exchange of these components. Such a setup would help us test with minimal downtime and maintain the flexibility and speed essential to our development process.

LOGICDATA has been a market-leading creator of advanced mechatronic and electronic components for adjustable furniture for over two decades. In this case, Andreas Pichler and the engineers needed to test DC electric motors: inline actuators with integrated control units.

In general, a DC electric motor consists of three main components:

1. The “rotor,” consisting of copper windings, motor windings,

2. The stationary part, the ‘stator,’ which includes a set of magnets, and

3. The ‘collector’ evenly distributes torque to the rotor.

The final design of the DC motor should provide the defined torque and power while maintaining high efficiency and effective heat management. Due to the complexity of the components installed in an electric motor, the testing phase is an essential step in validating the design points.

The test object is a black box in which the engineers only know the power input and output variables. Therefore, LOGICDATA uses the Dewesoft Motor Analysis module inside DewesoftX data acquisition software to determine the electric motor efficiency ‘η’ [%], which results from the relationship between output and input variables.

About LOGICDATA

The Austrian company LOGICDATA has been developing and manufacturing mechatronic systems for the furniture industry and beyond for 25 years. 13 million controllers and 4 million drives sold underline its core competence in synchronized motor and drive solutions.

More than 100 patents and 90 R&D experts speak for the quality and innovative strength of the Styrian company. It is characterized above all by its individually adapted products for various industries.

LOGICDATA's internal development of all drive system components aims to offer customized solutions optimally tailored to specific customer requirements. The company achieves these solutions by focusing on cost optimization for higher volumes. The critical aspects of this strategy include:

• Customized DC and PMSM motors developed for specific operating points

• Cost-optimized plastic, planetary, worm, and helical gearboxes

• Optimizing NVH and costs by reducing noise and vibrations at low cost.

• Developing brake systems of active (electromechanical) and passive systems

• Designing spindles in plastic, steel, and aluminum, optimized for efficiency and tribology

• Developing test stands for special needs In-house

The problem

Data generation is highly time-consuming due to complicated and lengthy measurement setups with many sensors and variants. In addition, the susceptibility to errors is high, as the measurement setup is complex. Simulations are only as precise as the data with which the engineers fed them. That is why measurement data makes a decisive contribution to the optimization of simulations.

In this case, the small drive is a complex system that enables various adaptations to customer requirements thanks to in-house developments and customized components. Efficient adaptation and understanding the influence parameters are crucial for all development phases. These phases range from rapid initial design and feasibility testing to prototype measurement, series stability, product life cycle management, and quality assurance.

In motor development, several elements are essential:

• The optimization and creation of data-based prediction models.

• Quality control of production parts at the component level, including the stator and rotor with active parts.

• Knowledge of performance metrics, such as maps and efficiency, for verification loops involving calculation and measurement.

The test stand - the solution

As part of an internal project, LOGICDATA developed a universal test bench that is a flexible solution for various measurement setups. This test bench can test various motor configurations, brakes, and transmissions and complete overall systems.

Innovative features

• Four-Quadrant Operation Mode: LOGICDATA implemented automatic detection of motor operating modes (motor/generator in forward and reverse directions), making monitoring performance and detecting real-time issues easier.

• Efficiency Mapping: DewesoftX allowed for efficiency mapping across different motor operating points, offering valuable insights into motor performance.

• Thermography Integration: The integration of thermal cameras into DewesoftX enabled the detection of hot spots on the motor, improving fault detection.

Mechanical design

LOGICDATA designed the test bay as a slide-rail system. All sensors, actuators, motors (DUT), etc., are mounted on separate slides. They share a common coaxial axis - the rotating measuring axis - and can be moved toward the axis using a handwheel. This degree of freedom enables the metal bellows couplings to be mounted quickly and easily. As soon as the entire measuring axis is mechanically connected, all slides can be self-locking locked via a lever. 

Another installation-friendly function is removing or replacing individual slides from the assembled measuring setup without moving other slides. Andreas Pichler and the engineers use the markings on the rail or slide for this purpose. This mechanical setup drastically reduces test stand set-up times.

Cable and signal interface

A versatile signal interface is above the measuring axis, which offers maximum flexibility about the electrical connection of the individual components on the test field. Thanks to the pluggable design of all signals, only those interfaces required for the respective measurement setup are used. This setup avoids long and confusing cabling and ensures the safety device interlocks correctly.

Integrated measurement and control technology

The heart of the test stand is the DEWE-43 data acquisition system. The engineers use four of its eight analog inputs for current/voltage level measurement. DSI adapters enable the automatic reading of sensor data, saving time on manual configuration and reducing configuration errors.

DSI adapters are TEDS IEEE 1451.4 equipped sensor adapters that turn Dewesoft DSUB9 universal analog input amplifiers into direct IEPE, charge, thermocouple, shunt, voltage, LVDT, or RTD input(s).

The remaining four inputs are available for universal use at the signal interface. The torque and speed signals of the transducers used are available as frequency-modulated signals at the digital inputs of the transducer.

Used test equipment

Dewesoft measurement setup

• DEWE-43a: Data acquisition system with measurement universal amplifiers and AD converters.

• Motor Analysis module in DewesoftX data acquisition and digital signal processing software.

• DSli-20A current shunt adapters for 50 Ω shunt with 0.01% accuracy for 20 mA current measurements.

• DSI-V-200 voltage adapter enables any DSUB9 analog input to accept ±200V voltage range and differential input via the BNC connector.

ETH Messtechnik

• ETH DRVL-I and DRVL-II: Dynamic torque and speed sensors.

Beckhoff PLC and Lenze actuators

• CX5130-0195: DIN-Rail industrial PC.

• MCS 09H41 and MCS 06C41: Servo motor.

• I950: Servo drive.

Controllable power supply

• Keysight Technologies E3640A

• TTi CPX400DP 

The test results

LOGICDATA tests both motor and generator operation. To avoid errors, Andreas Pichler and the engineers automated the detection of the motor's operating mode in DewesoftX. The automation allows potential issues to be quickly identified on the test stand monitor, ensuring efficient monitoring and error detection during testing.

Motor operational states tested

The engineers determine the operational state of a motor by the power flow direction of its connections. These are an electrical and a mechanical connection. If power supplies the system, the power sign is positive. If the sign is negative, energy dissipates from the system. 

The heat generated during operation is also regarded as dissipated power (negative), although its connecting element only exists in abstraction.

The engineers determine the electrical power via the product of the directly measured variables, such as current and voltage levels. The same applies to mechanical shaft power via rotational speed and torque. These variables must be measured with the correct sign since the input and output power of the motor might change during operation or test.

LOGICDATA implemented automatic detection of the operating modes from 1 to 5. Here, the sign rule automatically recognizes whether mechanical or electrical energy is added to or removed from the motor. The respective arrow thus indicates the direction of flow of the resulting power.

• Below 1, the electrical energy is supplied to the motor and converted into mechanical energy. The resulting heat losses dissipate from the system.

• Below 2, in contrast to 1, electrical energy is dissipated from added mechanical energy.

• In 3, if internal friction losses in the motor are more significant than the electrical power supplied, the motor is also driven mechanically to overcome these losses.

• Below 4, identify the idling of the motor even if no load is applied.

• Below 5, in the event of an error in the wiring of the current sensors, the electrical energy supplied is shown as power dissipated.

To summarise, the test bench operator can easily recognize the operating status and quickly identify faults, thus preventing the recording of incorrect measurement data.

Measurement setup for motor analysis

Engineers only operate the motor under test with DC components, so they can easily implement this in DewesoftX. They can define current, voltage, and mechanical variables such as motor speed and velocity in the power module. The motor analysis aims to automatically calculate the resulting electrical and mechanical power from the input variables, thus determining their ratio's efficiency. Such analysis is also possible for 3-phase systems.

Efficiency mapping is a helpful tool for testing and evaluating motors. The mapping visualizes motor efficiency via the motor speed and torque characteristic map. The motor efficiency map represents the exact ratio between mechanical and electrical power. In summary, it is helpful when deciding on a suitable motor or optimizing the operating points.

Thermography as a failure indicator

DewesoftX enables the integration of thermal cameras, such as the Optris IR cameras, via a USB interface.

During the test run, thermographic images of the test object are recorded at the defined frame rate (e.g., 30fps) and help to identify faults.

This way, local points with high temperatures, so-called hot spots, can be identified in the measured total losses, which more precisely become heat losses.

Conclusion

LOGICDATA’s innovative test bench design, supported by Dewesoft's technology, drastically improved the testing process for small electric motors. The modular and flexible design allowed for faster setup times, more reliable data acquisition, and enhanced efficiency analysis, which were critical in optimizing motor design and quality assurance. Automated operating mode detection and efficiency mapping provided valuable insights into motor performance, while thermography improved fault detection. 

“With our new setup, we’re now able to test components quickly and efficiently,” says Mechanical Expert Andreas Pichler and adds: “By automating the process, we’ve significantly reduced potential errors on both the software and hardware sides, ensuring smoother and more reliable operations.”

Overall, the test bench helped LOGICDATA achieve better precision, reduce testing time, and improve product quality, making it an invaluable tool in their development process.