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Analysis on the Current Situation of Turntable Technology

Date:2017-05-11 Author: Click:

Hydraulic turntable, hydraulic turntable as an important part of the machine tool is to ensure that all kinds of precision machining parts of the core equipment, widely used in various mechanical parts of the Processing. With the progress of society, the development of technology and high-end equipment to create new market demand, the mechanical parts of the processing accuracy requirements are getting higher and higher. Now turntable technology is the biggest confusion is the turntable of the degree of precision, concentricity, flatness and other precision how to meet the high-precision mechanical parts processing requirements. This problem has also become a technical problem in the current turntable field. Countries in the field of engineering and technical experts, thinking about the design of a lot of solutions, but the effect of improving the accuracy are unsatisfactory.

Electric turntable

How to solve the turntable ultra-high precision indexing and precise positioning, but also to meet the precision machinery parts in the processing process to ensure that the turntable does not produce angular displacement and flatness, concentricity error, become the current turntable field of global technical problems. In this paper, the author first of all the current turntable in the high-precision indexing and precise positioning of the advantages and disadvantages of the relevant technical analysis, and then on this basis put forward their own solutions for the industry colleagues reference.

We first from the conventional application of the most extensive worm gear drive turntable analysis:

First, the most commonly used turntable of its internal transmission for the worm gear drive. As the worm gear and worm contact surface for the sliding friction, so the frictional resistance, transmission efficiency is low. As the worm material is softer and the worm material hardness is large, so the worm wheel is easy to wear, resulting in increasing the indexing error, coupled with the worm gear isometric error (that is, the common law error), resulting in the degree of error , So the type of structural transmission turntable indexing accuracy is not high.

(This paragraph is about the degree of indexing accuracy)

In addition, since the worm gear and the worm can only engage 2.5 to 3 teeth, and can not make both sides of the spiral helical face and the two sides of the worm gear teeth at the same time close contact, so the output torque is not large, and the reverse gap is too large problem can not be solved The It is easy to cause the type of turntable in the processing of parts produced a larger angle deflection. In order to effectively control the angular deviation of the parts when processing parts, people think of the use of pneumatic and hydraulic brake locking output of the table, to overcome the processing of parts when the cutting force, control the angle of yaw generation. However, when the brake is locked, because the turntable itself has a large backlash and the output torque is small, the brake lock can increase the cutting resistance when the stationary torque counterces the machined part. However, when the brake is locked, Large angular displacement, resulting in processing parts in the positioning has produced a greater error.

 

According to this technical line, people try to overcome the loss of the accuracy of the worm gear through the envelope worm, the worm screw gradually thickening (that is, variable worm), or worm radial eccentricity, etc., but the results still can not solve the ultra-high precision Indexing problem. And because of the different worm and worm material, the difference in thermal expansion coefficient, resulting in long-term use caused by the temperature rise, so that the indexing accuracy is greatly reduced.

So the type of turntable is not possible to meet the processing needs of high-precision parts. But its advantages are low manufacturing cost, small size.

Second, in order to solve the above worm gear drive turntable congenital lack of technology, people think of the mouse through the teeth of the technical program. The principle is by fixing the rat tooth ring to the bottom of the turntable table, the other ring gear fixed on the turntable box through the worm gear driven lifted the table rotation indexing, and then fall with the fixed ring on the gear Upper and lower ring gear meshing. This structure of the turntable, the indexing accuracy and repeatability are very high, there are enough static torque to counter the cutting tool cutting resistance. But the minimum index can only be an integer, and in the table through the hydraulic jacking, and then rotate the index and then fall in the process, will produce the table plane and the central axis of the axis of the technical problems, so that the clamping in the work The reference plane and the axis of the parts on the platform can not meet their accuracy requirements. In particular, the multi-faceted box requires a high degree of concentricity between the face and the face, and the turntable can not meet its accuracy requirements. And then the type of turntable lift up in the table, and then turn the sub-sub-scale and then fall off the upper and lower ring gear, because the table and then rotate the indexing generated by the degree of error, will lead to the upper and lower ring gear when the teeth Deviation, when the table and the ring gear fall together, the upper ring gear and the ring gear will have a forced engagement, forced friction, and tooth surface wear and tear caused by its sub-precision and repeat the accuracy of reduced.

The advantages of this type of table is the high degree of precision, and there is enough static torque to overcome the cutting tool cutting resistance, the disadvantage is that can not meet the requirements of arbitrary indexing, in the process of dividing the table can not effectively guarantee the base and Spindle concentricity.

Third, through the above two forms of turntable indexing accuracy and positioning accuracy analysis, we can see it to meet the processing requirements of high precision parts of the inherent deficiencies. Optical experts and numerical control experts think of the use of grating closed-loop and computer digital processing to meet the turntable arbitrary indexing technical problems. There are two ways to implement: one is in the conventional worm gear transmission mechanism turntable output spindle on the installation of circular light through the computer system to implement high-precision indexing; the other is through the torque motor spindle on the installation of the circle Shaped grating, through the closed-loop feedback position signal to the computer system, to achieve precise indexing and positioning. Although these two forms of solution can achieve sub-degree and positioning accuracy of the ultra-precision, but these two forms of solutions still exist after the classification and repeat positioning accuracy how to overcome the brake lock, the accuracy does not change technical problem. Because of its small output torque, in order to overcome the tool cutting and vibration resistance must be through the indexing and positioning after the air pressure or hydraulic brake to lock the table or spindle, but in the lock will produce angular deflection, so that the original through The accuracy of the grating closed-loop system changes, so it actually reduces its accuracy.

In addition, the installation and use of grating on the turntable itself, the assembly accuracy and use of the environment is very high. For example, the turntable in the course of their own will produce temperature rise, the temperature will drop when the temperature drop in the process of falling air in the water will be gradually condensed with dust on the circular grating, so that the circular grating closed loop feedback Information to produce greater uncertainty, to the system indexing and repeated positioning to bring greater error, the most important thing is the accuracy of its loss is unpredictable. So what about the torque motor with a circular grating closed-loop system? Although the torque motor does not have mechanical transmission part, but its output torque is smaller, but also through the brake lock to meet the required parts required torque requirements, the same will produce latitude after the deviation and grating by the impact of condensed water mist, So that the accuracy of the lower.

Therefore, the above two programs can not meet the requirements of high precision parts processing. The key problem is that the raster is polluted and the error signal of the feedback position information is unpredictable, which makes the scrap rate of the finished part high. (Here delete a paragraph of the text)

To solve the current turntable high-precision indexing and positioning of technical problems, we believe that we must first find a breakthrough from the mechanical transmission, combined with CNC servo system to solve the current problems. First, we must solve the mechanical transmission part of the wear problem. Second, the mechanical transmission part must meet the strong output torque, so that it is sufficient to counter the processing of spare parts when the tool cutting and vibration, to ensure that the table does not produce the angle and plane and concentricity changes. Third, the mechanical clearance part of the reverse gap must be as small as possible, preferably zero backlash. Fourth, the transmission mechanism of the accuracy of the engagement of 0.003 mm-0.005 mm within the error. Through a long time a lot of practice has proved that the turntable only effectively solve these mechanical problems, coupled with the servo CNC system, in order to achieve both turntable indexing accuracy and repeat the accuracy of ultra-precision positioning requirements, but also to meet the processing needs of high-precision parts. Otherwise the turntable accuracy can only be used for testing, and can not be used in the actual high-precision machining.


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