Thread
thread is formed along the cylindrical surface or cone surface, along the helix, has a continuous projection and trench having the same cross-sectional shape. The thread formed on the cylindrical surface is called a cylindrical thread, and the thread formed on the conical surface is referred to as a conical thread. The thread formed on the outer surface of the rotary body is screwed, and the thread formed on the inner surface of the swivel body is said.
Processing threads are a lot, when the thread is added to the lathe, the lathe clamps the cylindrical workpiece through the trip chuck, and drives it as an equal speed rotation, the lathe feed mechanism with motor knife ( Standard threaded knife) Wait along the direction of the cylindrical axis, the vehicle tool tip cuts the triangular groove on the surface of the workpiece to form a triangular thread.
There is a track start point (at point, ie, the entry point) and the end point of the trajectory during the thread processing. In the threaded processing trajectory, there is a sufficient speed feeder section δ and the dropback section Δ'to eliminate the pitch errors caused by the servo hysteresis.
Task Implementation
The principle of photoelectric pulse generator. On the drain disc, there are two-ring stripes along the circles, the outer ring is a split line, for example: 1024, as the transmission pulse, only 1 inner ring. On the light bar, the distance between light-translucent stripes A, B, C, A and B should ensure that the striped BEN should be the same as another stripe on the drain optical disk when the stripe A and the drain optical disc. Map of 1/4 cycle. The photosensitive triode is placed behind each of the light bar, which constitutes an output channel.
The scattering light emitted by the bulb becomes parallel light after the concentrating mirror is concentrated, and when the drain disc is rotated synchronously with the spindle, since the stripes on the drain disc is coinctered with the stripes on the light bar, the photosensitizer is made By light, dark changes, causing changes in the inner current of the photosensitive tube, and the changed signal current outputs a rectangular pulse in the entire flow amplifier. Since the stripe A is combined with the drain disc stripe, the stripe B is dislocuted with another striped 1/4 period, so the waveform phase of the two channel outputs of A, B is also different from the 1/4 cycle.
Pulse generator The pulse of the optical disk inner ring is combined with the stripe C on the light bar to synchronize (start, also known as zero) pulse. With synchronous pulses, CNC lathes can achieve processing control, or as a quasi-stop signal of the spindle stop device. When the CNC lathe is threaded, the synchronous pulse uses the synchronous pulse as the control signal of the car tool into the knife point and the retracting point to ensure that the turning thread will not be buckled.
device requirements
1. CNC machine tool requirements for detecting elements and position detecting devices
(1) CNC machine tool requirements
detection elements are important components of detection devices, the main function is to detect displacement and Speed, send feedback signals. The minimum displacement of the displacement detection system can be measured is referred to as resolution. The resolution depends not only on the detection element itself, but also on the measurement circuit.
The main requirements for the detection elements are: 1 long life, high reliability, strong anti-interference ability; 2 meet accuracy and speed requirements; 3 use maintenance is convenient, suitable for machine tools; 4 cost 5 It is easy to join with the computer.
Different types of CNC machine tools are different from the accuracy and speed of the detection system. Usually large CNC machine tools are mainly designed to meet speed requirements, and medium, small and high-precision CNC machine tools are mainly designed to meet accuracy requirements. When you select the resolution and pulse equivalence of the measurement system, it is generally required to be a magnitude higher than the machining accuracy.
(2) CNC machine tool to the position detecting device
position detecting device is an important part of the CNC machine servo system. Its role is to detect displacement and speed, send feedback signals, constitute a closed loop or semi-closed loop control. The machining accuracy of the CNC machine tool is mainly determined by the accuracy of the detection system. Different types of CNC machine tools, the position detection elements, the accuracy requirements of the detection system and the highest moving speed of the measured components are different. The highest level of the detecting element and the system is that the maximum movement speed of the measurement member is as high as 240 m / min, and the resolution of the detection displacement (the minimum displacement can be detected) can reach 1 μm, such as 24 m / min to reach 0.1 μm. . The highest resolution can reach 0.01 μm.
CNC machine tools have the following requirements:
1 is small, the humidity has little effect, the work is reliable, and the accuracy can be maintained for a long time, and the anti-interference ability is strong.
2 can meet the accuracy and speed requirements in the mobile scope of the machine tool.
3 use maintenance, adapt to the machine working environment.
4 cost is low. Main shaft encoder introduction
2. Classification of location detecting devices
For different types of CNC machine tools, the following different detection methods can be employed due to working conditions and test requirements.(1) Incremental and absolute measurement
incremental detection mode only measures the displacement increment, and uses the number of digital pulses to represent unit displacement (ie minimum settings) The number of units is issued, and a measurement signal is issued each time a measurement unit. The advantage is that the detecting device is relatively simple, and any one of the midpoints can be used as a measurement starting point. However, in this system, the pitch is read by the measurement signal, once the accumulation is incorrect, the results will be completely wrong. In addition, when the failure (such as power off) can no longer find the correct position before the accident, after the accident is excluded, the workbench must be moved to the starting point re-count to find the correct position before the accident. Pulse encoders, rotary modulators, induction synchronizers, gratings, magnets, laser interferometers, etc. are all incremental detecting devices.
The absolute measurement method is measured is an absolute coordinate position value of the measured component in a certain absolute coordinate system, and is expressed in binary or decimal digital signals, generally converted to a pulsed digital signal. In the future, it can be sent to the comparison and display. In this way, the higher the resolution requirements, the more complicated structure. Such a measuring device has an absolute pulse coding disk, a three-speed absolute encoding disk (or a multi-zone absolute coda), and the like.
(2) Digital and analog measuring
Digital detection is to quantify the measured unit to be quantified in digital form. The measurement signal is generally a electrical pulse, and it can be sent directly to the CNC system to perform comparison. Such a detection device has a pulse encoder, a grating. Digital detection has three features.
1 is measured to convert to the pulse number, easy to display and process;
2 measurement accuracy depends on the measurement unit, and the range is basically unrelated; but there is a cumulative error difference;
3 detection device is relatively simple, and the pulse signal is strong in disturbance.
The analog testing is to indicate the measured variable, such as the magnitude of the voltage, phase change, and the like. When doing precise simulation detection in a large number of times, there is a high technical requirement, and the simulation detection in the CNC machine tool is mainly used for small range measurements. The analog detecting device has a speed generator, a rotary modulator, an inductive synchronizer, and a magnetic scale. The main features of simulation detection have the following.
1 is directly detected, no need to quantify.
2 can achieve high precision measurements in a small amount.
3 can perform direct detection and indirect detection.
The position detecting device is mounted directly on the execution unit (ie, the end piece), the linear displacement or angular displacement of the execution component end piece is directly measured, and can be referred to as direct measurement, which can constitute a closed loop feed servo system, measurement method. There is a linear displacement of a linear grating, a linear sensing synchronizer, a magnetic gate, a laser interferometer, and the like; since this detection method is measured by a linear displacement of the machine tool. The advantage is to directly reflect the linear displacement of the table. The disadvantage is that the detection device is long, which is a big limit for large machine tools.
The position detecting device is mounted on the transmission element or the drive motor shaft in front of the execution unit, and the angular displacement is measured, and the linear displacement amount of the actuator can be obtained after the transmission ratio transform, such as indirect measurement, A semi-closed loop servo feed system. The pulse encoder is applied to the motor shaft. Indirect measurements are reliable and convenient, no length restrictions; it is the disadvantage to add a straight line transition into a rotational motion of the transmission chain error in the detection signal, thereby affecting the measurement accuracy. It is generally necessary to compensate for the transmission error of the machine, in order to increase the positioning accuracy.
In addition to the above position detecting device, the servo system often includes an element of the detection speed to detect and regulate the rotational speed of the engine. Common speeding elements are speed of speed.
Selection Precautions
one. Conventional profile of an absolute value encoder: 38mm, 58mm, 66mm, 80mm.100mm. II. Absolute value encoder is divided into: single-ring, multi-circle.three. The bus encoder is divided into: secondary absolute value encoder, the light absolute value encoder. The bus encoder is widely divided into: side outline, and out of line. The bus encoder is divided into: 6mm, 8mm, 10 mm, 12mm, 14mm, 25mm. 6. The bus encoder is divided into: shaft, blind hole, through hole.seven. Bus encoder protection is divided into: IP54-68. Bus encoder installation is divided into: clamping flange, synchronous flange, clamping strip synchronous flange, blind hole (spring sheet, tightening), pass
hole (spring sheet, key pin) Nine. The absolute value encoder accuracy is divided into: single-zone accuracy and multi-circle accuracy, adding a total precision, which is usually the number (regular 24
, 25, 30, 32). ..).ten. Absolute value encoder communication protocol baud rate: 4800 ~ 115200 bit / s, wood considers 9600 bit / s. Refresh cycle is about 1.5 ms 11. Encoder output optional: SSI, 4-20MA, PROFIBUS-DP, DeviceNet, Parallel, binary code, BESM58, BISS, ISI,
CANopen, Endat and HiPerface, etc.