The general structure of an industrial robot's electric servo system consists of three closed-loop control loops: current loop, speed loop, and position loop. Typically, for AC servo drives, multiple functions such as position control, speed control, and torque control can be achieved by manually setting their internal functional parameters.
01 How to correctly choose between servo motors and stepper motors?
It mainly depends on the specific application. Simply put, you need to determine: the nature of the load (e.g., horizontal or vertical load), torque, inertia, speed, accuracy, acceleration/deceleration requirements, higher-level control requirements (e.g., port interface and communication requirements), and the primary control method (position, torque, or speed control). Also, determine whether the power supply is DC, AC, or battery-powered, and the voltage range. Based on this, determine the model of the motor and the corresponding driver or controller.
02. Should I choose a stepper motor or a servo motor system?
In fact, the choice of motor should be based on the specific application, as each type has its own characteristics.
03 How to use a stepper motor driver?
Choose a driver with a current greater than or equal to that of the motor. For applications requiring low vibration or high precision, a microstepping driver can be used. For high-torque motors, use a high-voltage driver whenever possible to achieve good high-speed performance.
04 What are the differences between 2-phase and 5-phase stepper motors, and how do you choose between them?
Two-phase motors are inexpensive, but they vibrate more at low speeds and their torque drops rapidly at high speeds. Five-phase motors, on the other hand, vibrate less, have better high-speed performance, and are 30-50% faster than two-phase motors, making them a viable alternative to servo motors in some applications.
05 When should a DC servo system be selected, and what are the differences between it and an AC servo system?
DC servo motors are divided into brushed motors and brushless motors.
Brushed motors are low in cost, simple in structure, have high starting torque, wide speed range, and are easy to control. They require maintenance, but maintenance is convenient (replacing carbon brushes). They generate electromagnetic interference and have environmental requirements. Therefore, they can be used in cost-sensitive general industrial and civilian applications.
Brushless motors are small in size, lightweight, powerful, fast-responding, high-speed, low-inertia, smooth-rotating, and stable in torque. While their control is complex, they are easily made intelligent. Their electronic commutation is flexible, allowing for either square wave or sine wave commutation. These motors are maintenance-free, highly efficient, operate at low temperatures, have minimal electromagnetic radiation, and a long lifespan, making them suitable for various environments.
AC servo motors are also brushless motors, and they are divided into synchronous and asynchronous motors. Currently, synchronous motors are generally used in motion control because they have a wide power range and can achieve very high power. They have high inertia, low maximum rotational speed, and their speed decreases rapidly as power increases. Therefore, they are suitable for applications requiring low-speed, stable operation.
06 What issues should be considered when using a motor?
The following checks must be performed before powering on:
Is the power supply voltage appropriate (overvoltage may damage the drive module); the +/- polarity of the DC input must not be connected incorrectly; is the motor model or current setting on the drive controller appropriate (do not set it too high at the beginning)?
The control signal lines should be securely connected, and shielding should be considered in industrial settings (e.g., using twisted-pair cables).
Don't connect all the necessary wires at the beginning. Only connect the most basic system. After it is running well, then connect the rest gradually.
It is essential to clarify the grounding method, whether to use floating grounding without connection.
During the first half hour of operation, closely observe the motor's status, such as whether its movement is normal, the sound, and the temperature rise. If any problems are found, stop the machine immediately for adjustment.
07 When a stepper motor starts running, sometimes it moves briefly and then stops, or it moves back and forth in place. Sometimes it even loses steps during operation. What is the problem?
The following aspects should generally be considered when conducting an inspection:
Whether the motor torque is large enough to drive the load is important. Therefore, we generally recommend that users select a motor with a torque that is 50% to 100% greater than the actual requirement. This is because stepper motors cannot be overloaded, even momentarily, as this can cause them to lose steps, or in severe cases, stop or move irregularly and repeatedly in place.
Is the current of the input step pulse from the host controller large enough (generally >10mA) to ensure stable conduction of the optocoupler? Is the input frequency too high, causing it to be unreceived? If the output circuit of the host controller is a CMOS circuit, then a CMOS input type driver should also be selected.
Is the starting frequency too high? Is there an acceleration process set in the starting program? It is best to start accelerating from the motor's specified starting frequency to the set frequency, even if the acceleration time is very short. Otherwise, it may be unstable or even in an inert state.
This situation can sometimes occur when the motor is not properly secured, and it is normal. This is because it causes strong resonance in the motor, leading to a loss of synchronization. The motor must be properly secured.
For a 5-phase motor, if the phases are connected incorrectly, the motor will not work.
08 I want to control the servo motor directly via communication, is that possible?
Yes, it's possible and relatively convenient, but there's a speed issue. It's suitable for applications where response speed isn't critical. If rapid response to control parameters is required, a servo motion control card is best. These cards typically have a DSP and high-speed logic processing circuitry to achieve high-speed, high-precision motion control, such as S-curve acceleration and multi-axis interpolation.
09 Is it good to use a switching power supply to power stepper and DC motor systems?
Generally, it's best to avoid this, especially for high-torque motors, unless a switching power supply with more than twice the required power is used. This is because motors operate as large inductive loads, creating instantaneous high voltage at the power supply terminals. Switching power supplies have poor overload performance and will shut down under protection, and their precise voltage regulation is unnecessary, potentially damaging both the power supply and the driver. A conventional DC power supply with a toroidal or R-type transformer can be used instead.
10. Is it possible to control a stepper motor using a DC voltage of ±10V or 4~20mA?
Yes, but an additional conversion module is required.
11. Can a servo motor with encoder feedback be controlled by a servo driver with only a tachometer port?
Yes, but you'll need an encoder-to-tachometer signal module.
Can the encoder part of the 12 servo motor be disassembled?
Do not disassemble, as the quartz plates inside the code disk are easily broken, and once dust gets inside, the lifespan and accuracy will not be guaranteed, requiring professional inspection.
13. Can stepper and servo motors be disassembled for inspection or modification?
No, it's best to have the manufacturer do it. Without specialized equipment, it's very difficult to reassemble it after disassembly, and the clearance between the motor's rotor and stator cannot be guaranteed. The performance of the magnets will be damaged, potentially causing demagnetization, and the motor torque will decrease significantly.
14. Can a servo controller sense changes in external load?
If you encounter set resistance, stop, return, or maintain a certain amount of thrust to continue.
15. Can domestically produced drives or motors be used in conjunction with high-quality foreign motors or drives?
In principle, it's possible, but you must understand the motor's technical parameters before using it. Otherwise, it will greatly reduce the expected performance and may even affect long-term operation and lifespan. It's best to consult with the supplier before making a decision.
16. Is it safe to drive a motor using a DC power supply voltage greater than the rated voltage?
Normally this isn't a problem, as long as the motor operates within its set speed and current limits. Because motor speed is proportional to its line voltage, choosing a specific power supply voltage won't cause overspeed, but it might lead to driver malfunctions.
In addition, it is necessary to ensure that the motor meets the minimum inductance requirements of the driver, and also to ensure that the set current limit value is less than or equal to the rated current of the motor.
In fact, if you can make the motor run relatively slowly (below the rated voltage) in your designed device, that's good.
Operating at a lower voltage (and therefore a lower speed) results in less brush bounce, less brush/commutator wear, lower current consumption, and a longer motor life.
On the other hand, if the size of the motor is limited and the performance requirements necessitate additional torque and speed, overdriving the motor is also possible, but it will sacrifice the product's lifespan.
17. How do I choose the right power supply for my application?
It is recommended to choose a power supply voltage 10%-50% higher than the maximum required voltage. This percentage varies depending on Kt, Ke, and the voltage drop within the system. The driver's current should be sufficient to deliver the energy required by the application. Remember that the driver's output voltage differs from the supply voltage, therefore the driver's output current also differs from the input current. To determine the appropriate supply current, calculate all the power requirements of the application, then add 5%. The required current value can be calculated using the formula I=P/V.
It is recommended to choose a power supply voltage 10%-50% higher than the maximum required voltage. This percentage varies depending on Kt, Ke, and the voltage drop within the system. The driver's current should be sufficient to deliver the energy required by the application. Remember that the driver's output voltage differs from the supply voltage, therefore the driver's output current also differs from the input current. To determine the appropriate supply current, calculate all the power requirements of the application, then add 5%. The required current value can be calculated using the formula I=P/V.
18. What operating mode can I choose for a servo drive?
Different modes are not all present in all drive models.
19. How are the drivers and system grounded?
Do not connect the non-isolated port of the DC bus or the ground of a non-isolated signal to earth if there is no isolation between the AC power supply and the DC bus of the driver (such as a transformer). This may result in equipment damage and personal injury. Because the AC common voltage is not grounded, there may be a very high voltage between the DC bus ground and earth.
In most servo systems, all common ground and earth ground are connected together at the signal end. Ground loops created by multiple earth ground connection methods are easily affected by noise, resulting in current at different reference points.
To maintain a constant command reference voltage, the driver's signal ground should be connected to the controller's signal ground. It will also be connected to the ground of an external power supply, which will affect the operation of the controller and the driver (e.g., the encoder's 5V power supply).
Grounding the shielding layer is relatively difficult and involves several methods. The correct grounding point for the shielding is at a reference potential point within its circuitry. This point depends on whether the noise source and receiver are grounded simultaneously or floating. It's crucial to ensure the shielding is grounded at the same point so that ground current does not flow through it.
Why can't the reducer be perfectly matched with the motor at the standard torque point?
If we take into account the maximum continuous torque generated by the motor after passing through the reducer, many reduction ratios will far exceed the torque rating of the reducer.
If we were to design each reducer to match full torque, there would be too many combinations of internal gears in the reducer (larger volume, more material).
This would result in a high product price and violate the product's "high performance, small size" principle.
21. How to select electric cylinders, slides, and precision platforms? How are their costs calculated?
The key to choosing actuator products is understanding your requirements for motion parameters. You can determine the specific motion parameters and other technical conditions based on your application. These parameters must meet your actual needs, satisfying the application requirements while allowing for some margin, but not setting them too high, otherwise the cost could be several times that of a standard product. For example, if 0.1mm accuracy is sufficient, don't choose parameters with 0.01mm. The same applies to other parameters such as load capacity and speed.
Another suggestion for users is that, unless absolutely necessary, avoid simultaneously demanding high levels of the three main parameters: push-pull force or load capacity, speed, and positioning accuracy. This is because an actuator is a high-precision, high-tech mechatronic product. During design and manufacturing, we need to consider various aspects such as mechanical structure, electrical performance, material properties, materials, and processing methods, and select appropriate component motors, drive controllers, feedback devices, as well as guide rails, lead screws, support bases, and other mechanical systems of different precision levels to achieve the required overall motion parameters. It's a product where a single change affects the entire system. Of course, if you have high-requirement products, we can still meet your needs, but the cost will increase accordingly.
