Industrial robot peripheral motion control primarily consists of three key components: servo control, step control, and frequency conversion control. Let's explore each of these in detail.
**Servo Control**
**1. Working Principle of AC Servo Motor**
An AC servo motor features a permanent magnet rotor. The driver controls the U/V/W three-phase motor, generating an electromagnetic field that causes the rotor to rotate. An encoder provides feedback from the motor to the driver, which compares this with the target value to adjust the rotor’s rotation angle. The precision of the servo motor is determined by the resolution (number of lines) of the encoder.
**2. Components and Classification of the Servo System**
A servo system is a control system designed to manage position, angle, speed, angular velocity, acceleration, and force. It can be classified based on control structure (open-loop or closed-loop) and drive components (stepper motor, DC motor, or AC motor).
**3. Characteristics of AC Servo Motors**
- High positioning accuracy (up to 0.036 degrees).
- Fast response time.
- Easy to control and implement.
- Wide range of models for different applications.
- Full-closed loop control for real-time monitoring and adjustment.
**4. Servo System Structure**
[Image: Servo system structure diagram]
**5. Steps for Servo Control Selection**
- Determine mechanical specifications such as load, stiffness, etc.
- Confirm motion parameters like speed, stroke, and accuracy.
- Select motor inertia, load inertia, and rotor inertia.
- Choose motor speed and rated torque.
- Determine mechanical position resolution.
- Select the appropriate motor model based on the above criteria.
**6. Applications of Servo Control**
[Image: Examples of servo control applications]
**Step Control**
**1. Working Principle of Stepper Motor**
A stepper motor converts electrical pulses into angular displacement. Each pulse drives the motor to rotate a fixed angle (step angle), allowing precise positioning through pulse count. Pulse frequency controls speed and acceleration. Stepper motors are widely used in open-loop systems due to their high accuracy without error accumulation.
**2. Classification of Stepper Motors**
Common types include:
- **Permanent Magnet (PM):** Two-phase, small torque, step angles of 7.5° or 15°.
- **Reactive (VR):** Three-phase, large torque, step angle of 1.5°, but with higher noise and vibration.
- **Hybrid (HB):** Combines PM and VR, two-phase (1.8°) or five-phase (0.72°), most commonly used.
**3. Stepper Motor System**
[Image: Stepper motor system diagram]
**4. Key Parameters of Stepper Motor**
- Phase number, number of steps, step angle, holding torque, static torque, step accuracy, out-of-step, offset angle, maximum no-load starting frequency, and running moment frequency characteristics.
**5. Selection of Stepper Motor**
- Step angle based on required accuracy.
- Static torque based on load (typically 2–3 times the friction load).
- Current selection based on torque-frequency characteristics.
**6. Characteristics of Stepper Motor**
- Accuracy of 3–5% per step, non-cumulative.
- Maximum temperature around 130°C.
- Torque decreases with increasing speed.
- Operates smoothly at low speeds but may fail at higher speeds.
- Typically used below 1000 RPM.
**Performance Comparison Between Stepper and Servo Motors**
- **Control Precision:** Servo motors have higher precision due to encoder feedback.
- **Low-Speed Stability:** Servo motors run smoothly, while steppers may vibrate.
- **Overload Capability:** Servos handle overload better than steppers.
- **Response Time:** Servos accelerate faster (milliseconds vs. hundreds of milliseconds).
- **Torque-Frequency Characteristics:** Servos maintain constant torque, while steppers lose torque at high speeds.
**Frequency Control**
**1. Introduction to General Motors**
The three-phase squirrel-cage induction motor is the most common type. Its structure includes stator, rotor, and windings. It operates based on electromagnetic induction principles.
**2. Inverter Principle and Composition**
An inverter adjusts the speed of an AC motor by changing the power supply frequency. It consists of a rectifier, DC link, inverter, and braking circuit.
- **Rectifier:** Converts AC to DC using diodes or transistors.
- **DC Link:** Smooths the DC voltage using capacitors or inductors.
- **Inverter:** Converts DC back to AC with variable frequency.
- **Braking Circuit:** Dissipates regenerative energy to prevent overvoltage.
**3. Application of Inverters**
Inverters are used in adjustable-speed drives for industrial applications such as pumps, fans, and conveyor belts. They improve energy efficiency and provide smooth speed control.
[Image: Inverter application examples]
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