The main components of the mining machinery such as the front and rear frame of the electric scraper, the gearbox of the sprayer, and the gearbox of the motor car generally need to be processed on a horizontal boring machine. The T612 boring machine of our factory has been aging seriously after nearly 30 years of operation, and the precision is lowered, which cannot meet the requirements of high-precision machining.
In the overhaul of the equipment, the digital display was successfully modified, and a raster digital display system was installed. The system uses the moiré generated by the grating movement to combine with the electronic circuit and the single chip microcomputer to complete the automatic measurement of the displacement. The amount of displacement is displayed in numbers. The working principle and practical application of the system are described below.
First, the hardware introduction of the raster digital display systemThe AT89S51 is used to process the acquisition signal chip. It supports the ISP online programming function and has two 16-bit timer/counters internally. The keyboard and display section adopts the intelligent display driver chip WH8280 which has the SPI serial interface function and can simultaneously drive the 8-bit common cathode digital tube. It contains a decoder inside, can directly accept hexadecimal code or BCD code, and has two kinds of decoding modes at the same time, which can be segmented. With a chip select signal, it is convenient to implement a display with more than 8 bits or a keyboard interface with more than 64 keys. The grating displacement measuring system hardware mainly consists of a grating discriminating circuit, an AT89S51 single chip microcomputer, a WH8280 keyboard and a digital tube circuit. The block diagram of the displacement measurement system is shown in Figure 1.
The grating is composed of a light source, a lens, a scale grating (main grating), an indicator grating (sub-grating), and a photoelectric element. When the main grating and the sub-grating are placed in a relatively oblique arrangement with a small angle of θ, the lines on the two gratings are intersected. Under the illumination of the light source, the black lines in the small area near the intersection point overlap to form a bright and dark moire fringe and the grating lines are arranged in a substantially vertical direction. When the scale grating moves along the vertical reticle relative to the main grating, the moire fringes follow it. The light intensity of the moiré fringes changes approximately as a positive (co) chord curve, and the law of photocurrent induced by the photoelectric element is approximately a positive (co) chord curve. After amplification by the amplifier and shaping circuit, two sine waves or square waves with a phase difference of 90° are obtained, which are sent to the raster digital display for counting display.
Third, the grating precautionsThe main ruler is usually mounted on the workbench of the machine. The readhead is mounted on the stationary part of the machine and installed as far as possible under the main ruler. The selection of the mounting position must pay attention to the direction of the chip, cutting fluid and oil splash.
1. Mounting base of the grating sensor
When the grating is used in the transformation of the old machine tool, there is generally no ideal mounting surface. It is necessary to process and make a suitable pedestal. The material is preferably aging-treated cast iron to ensure small deformation and stable geometric precision. The pedestal is passed through a milling machine. Grinding machine processing. The parallelism of the base to the machine guide surface is adjusted by the equal height pad or by the constant pressure screw, and the parallelism is required to be within 1.1mm/1000mm. The total error of the base of the readhead and the base of the ruler shall not exceed ±0.2mm. During installation, adjust the position of the reading head to achieve a parallelism of about 0.1 mm between the reading head and the scale body. The distance between the reading head and the scale body is about 1~1.5 mm.
2, the main ruler installation of the grating sensor
Use the adjusting screw to fix the grating main ruler on the base of the worktable mounting surface, fix the dial gauge to the bed, move the workbench, measure the parallelism between the main ruler plane and the movement direction of the machine guide rail, and adjust the screws to make the main ruler parallelism. When it is within 0.1mm/1000mm, tighten the fixing screw completely. When installing the grating main ruler, it should be noted that when the main ruler of the grating exceeds 1.5M, it is not allowed to install only the two ends. It is necessary to install the support in the main ruler body. It is better to use a clamp to catch the midpoint of the ruler (or some points). ).
3. Limiting device of grating sensor
After the grating sensor is completely installed, in order to avoid the reading head colliding with the two ends of the main ruler when the machine product is moved, the grating scale is damaged, and the limit device must be installed on the machine guide rail.
4, grating sensor read head installation
The reading method of the read head is similar to that of the main ruler. The parallelism between the read head and the grating main rule is guaranteed to be within 0.1 mm, and the gap between the read head and the main ruler is controlled within 1~1.5 mm.
5. Installation of protection device
Through the above work, the installation of the grating sensor is completed. However, for general machine tool processing environments, there are more iron filings, cutting fluids and oil stains. Therefore, the grating sensor should be equipped with a protective cover. The shield is determined according to the cross-sectional dimension of the grating sensor. Usually, the rubber seal is used to make it have a certain waterproof and oil proof ability.
Fourth, grating sensor use precautions(1) The grating sensor and the digital display meter socket should be turned off after the power is turned on and off.
(2) Clean the chips and oil splashed on the ruler in time to prevent any foreign matter from entering the inside of the grating sensor housing.
(3) Regularly check whether the mounting screws are loose.
(4) To extend the life of the dust seal, evenly apply a thin layer of silicone oil on the seal, taking care not to splash on the glass grating scribe surface.
(5) In order to ensure the reliability of the grating sensor, the grating surface and the indicator grating surface can be cleaned with the ethanol mixture (50% each) at regular intervals to keep the glass grating surface clean.
(6) The grating sensor is strictly prohibited from violent vibration and beating, so as not to damage the grating scale. If the grating scale is broken, the grating sensor is invalid.
(7) Care should be taken to prevent oil stains and water from contaminating the grating surface, so as not to damage the stripe distribution of the grating scale and cause measurement errors.
(8) The grating sensor should try to avoid working in an environment with severe corrosion, so as to avoid corrosion of the grating chrome layer and the grating scale surface, and destroy the quality of the grating ruler.
V. Effect and benefit estimationBefore the digital display is installed, the operator needs to frequently stop and measure the size repeatedly to control the machining accuracy, which is greatly affected by the worker's operation proficiency. The addition of digital display can reduce the impact of measurement error, and the accuracy can be controlled within 0.01-0.03mm. Take the shotcrete reducer as an example. It takes 3 classes (1300 minutes of work) to complete before installing the digital display. Now it can be completed in less than two shifts, improving efficiency by 40%. Later, the C5335, C5325 vertical car and X53T milling machine of our factory have also been modified by digital display system, and the economic benefits are obvious.
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