1. Explanation of terms:
1. Machine tool numerical control technology: a technology that uses digital information to control the movement of the machine tool and its processing process
2. Closed-loop control system:
The output of the system controls the system Actions have a direct influence on the control system. With a position detection device, it is installed on the executive components such as the machine tool holder or workbench, and has high control accuracy; but the stability of the system is affected, debugging is difficult, and the structure is complex and expensive
3. AC synchronous motor:
Refers to the type of motor whose speed is determined by the frequency of the applied alternating current.
4. Stepper motor:
is an electromagnetic device that converts electrical pulse signals into angular displacement.
5. Point control system:
refers to a system in which the CNC system only controls the tool or the machine tool table, and moves from one point to another point accurately, and the trajectory between points does not need to be strictly controlled.
6. Modal code:
A group of codes that can cancel each other. Once these codes are executed, they will be valid until they are canceled by the same group of codes.
7. Interpolation calculation:
Interpolation calculation means that the numerical control device describes the shape of the workpiece contour through calculation according to the input basic data, and sends feed pulses to each coordinate according to the calculation results while calculating. Corresponding to each pulse, the machine tool moves in the corresponding coordinate direction One pulse equivalent distance, so that the workpiece can be machined into the shape of the required contour.
A device or device that can sense the specified measured piece and convert it into a usable signal according to a certain rule.
9. Economical CNC system:
From the perspective of control method, it is economical Type CNC system generally refers to the open-loop CNC system. It is mainly composed of microcomputer, feed drive, spindle drive, switch control, communication interface and software.
10. Numerical control device:
is the core of numerical control equipment, which mainly processes and judges the input data signal. And issue the command to assign the execution command to the servo system
11. The non-modal code
is only valid in the specified program segment and will be canceled at the end of the program segment.
12. Pulse equivalent:
The displacement of the moving parts of the machine tool relative to each pulse signal is called pulse equivalent.
13. Standard CNC system:
The standard CNC system is generally controlled by the program Composed of input/output equipment, communication equipment, microcomputer system, programmable controller, spindle drive, feed drive and position detection, etc., the functions are relatively complete, and the control accuracy and speed are relatively high, usually used in closed-loop systems.
14. Continuous control system:
refers to the CNC system that can perform strict continuous control on two or more coordinate axes at the same time.
15. Open-loop control system:
is the control of the system A control system in which the inputs are not affected by the outputs. There is no position detection device, and the signal is unidirectional. The structure is simple, the manufacturing cost is low, the price is cheap, and the precision is not high
16. The G code of the preparation function:
The preparation function word of the machine tool. regulationSet the machine tool motion line type, coordinate system, coordinate plane, compensation, pause and other operations.
17. Interpolation calculation:
means that the CNC system describes the shape of the workpiece contour through calculation according to the input basic data (such as starting point, end point, etc.), and sends feed to the coordinates according to the calculation result while calculating. Instructions are called interpolation calculations.
18. Step angle:
is the mechanical angle that the rotor rotates for a pulse signal without a reduction gear. It can also be described in this way: every time the stator control winding changes its energization mode, it is called a beat. The mechanical angle that the rotor rotates in each beat is called the step angle
2. Questions and answers:
1. What is the step angle of the stepping motor? What parameters are related to the size of the step angle?
Every time the driver inputs an electric pulse signal to the stepping motor, the stepping motor will rotate an angle, which becomes the step angle. Its magnitude is proportional to the number of electrical pulse signals.
2. What is the purpose of left shift normalization in DDA interpolation?
Make the feed rate uniform and improve the quality of the processed surface
3. Try the block diagram to describe the software interpolation process of the point-by-point comparison method?
4. What are the basic components of CNC machine tools?
The main body of the machine tool, the numerical control system (operating panel, input and output equipment, cnc device, servo unit, driving device and measuring device, PLC machine tool I/O circuit and device), peripheral technology
5, point-by-point comparison method What are the four working beats of imputation?
Deviation judgment, coordinate feed, new deviation calculation, end point comparison.
6. What is the difference between an incremental encoder and an absolute encoder?
The difference lies in the structure of the code track on the photoelectric code disc and the type of output signal.
7. What are the two states of the stepping motor when it is working?
8. What are the characteristics of point control and continuous control systems?
Point position: It only realizes the precise positioning movement of the tool relative to the workpiece from one point to another point; there is no control requirement for the trajectory; no processing is performed during the movement.
Continuous: Control multiple coordinate axes at the same time to make them move in coordination (coordinate linkage), so that the tool moves relative to the workpiece according to the trajectory and speed specified in the program, and performs continuous cutting during the movement.
9. Description What is the difference between closed-loop and semi-closed-loop control systems?
Semi-closed loop: with a position detection device, often installed on the servo motor or the end of the screw; excluding the large inertia links such as the screw nut pair and the machine tool table guide rail pair, stable control characteristics can be obtained, and Debugging is more convenient.
Closed loop: with a position detection device, installed on the executive components such as machine tool holder or workbench, the control accuracy is high; but the stability of the system is affected, debugging is difficult, and the structure is complex and expensive.
10. How to determine the coordinate axis of CNC machine tool?
Z coordinate axis: the feed axis parallel to the spindle axis. The positive direction of Z coordinate specifies: the direction that the tool moves away from the workpiece. The xyz axes satisfy the right hand criterion.
11. What is the essence of interpolation operation in the numerical control system?
is an iterative operation.
12. Why should the ball screw nut pair be pre-tightened?
Increase axial rigidity; eliminate backlash and improve transmission accuracy.
13. Briefly describe the working principle of the stepping motor?
14. Why does the open-loop servo system use a stepping motor as the drive element?
① Adjustable speed, wide range of speed adjustment: changing the frequency can change the speed, and the frequency is wide.
② The output angle is controllable: controlled by the number of pulses.
③ High sensitivity: not easily affected by various interference factors.
④ High output precision: after one turn, the corner error is “0”, no error accumulation
15. Briefly describe the working principle of the PWM speed control system of the DC servo motor?
The principle is to adjust the average value of the control voltage V2 by changing the width of the voltage pulse to obtain different control voltages V2 to achieve the purpose of speed regulation
16. Briefly describe the SPWM speed regulation system of the permanent magnet AC synchronous motor How does it work?
a three-phase sine wave control signal: three-phase symmetrical common sine wave with variable frequency and amplitude;
b triangular wave generator: generate triangular carrier;
c three-phase sine wave control signal and triangular carrier After the SPWM main circuit is modulated, it outputs a modulated wave with the same frequency as the three-phase sine wave control signal to drive the motor;
d Change the frequency of the three-phase sine wave control signal to change the power supply frequency of the motor stator to achieve the purpose of speed regulation .
17. What is the purpose of the ring distribution driven by the stepping motor? What are the implementation forms? What is the form of the signal output from the numerical control system to the stepper motor driver?
Control the on-off of the stator winding to realize the operation and commutation of the stepper motor; hardware and software two ways of implementation; pulse signal
18. What are the transmission characteristics of the ball screw nut pair?
① High transmission efficiency: small rolling friction resistance and high transmission efficiency.
② Good rigidity: Pre-tightening measures can be used to improve axial rigidity.
③ Stable movement and high transmission precision: Pre-tightening is used to eliminate backlash to improve transmission precision.
④ Long service life: small rolling friction and wear.
⑤ The motion is reversible and cannot be self-locking: it can convert rotation into linear motion, and also convert linear motion into rotation
19. What are the methods for eliminating the gap in gear transmission?
Rigid adjustment method, flexible adjustment method
20. What kind of transmission chain is the thread transmission chain of horizontal lathe?
External connection transmission chain
21. What is the general process of NC machining program compilation?
Analyze the part drawing, determine the technological process; calculate the motion trajectory and mark the geometric dimensions; compile the processing program and preliminary inspection; prepare the control medium; check the program and try cutting.
22. Why is it necessary to take uniform measures for the feed speed in the digital integral method?
During the interpolation due to the digital integral method, regardless of the length of the line segment, the same number of cumulative calculations are performed, that is, the interpolation time is the same. Therefore, the tool moves faster when the stroke is long, and the tool moves slowly when the stroke is short, resulting in the feed rate during the machining process.The speed is uneven, which directly affects the surface quality of processing. Therefore, the feed rate must be homogenized.
23. How does an incremental encoder (also known as a pulse encoder) measure the rotational speed?
The shaft speed can be obtained through the pulse frequency
24. What parameters of the pulse determine the angle, speed and direction of rotation of the stepping motor?
Number of pulses; pulse frequency; power sequence.
25. What is a sensor?
A device or device that can sense the specified measured object and convert it into a usable signal according to certain rules.
1. Explanation of terms: