Qingdao Vanhon Machinery Technology Co.,Ltd.

Industry News
Rack and pinion drive
Mar 22, 2022

Ⅰ. Introduce the types of gear racks

Gears can be classified by tooth shape, gear shape, tooth line shape, surface on which the gear teeth are located, and manufacturing method, as follows:

1. Gears can be classified into tooth profile curve, pressure angle, tooth height and displacement according to tooth shape;

2. Gears are divided into cylindrical gears, bevel gears, non-circular gears, racks, and worm-worm gears according to their shapes;

3. Gears are divided into spur gears, helical gears, herringbone gears, and curved gears according to the shape of the tooth line;

4. According to the surface gear where the gear teeth are located, the gear is divided into external gear and internal gear, among which the tip circle of the external gear is larger than the root circle, while the tip circle of the internal gear is smaller than the root circle;

5. According to the manufacturing method, gears are divided into casting gears, cutting gears, rolling gears, sintering gears, etc.

6. Racks are mainly divided into spur gears and helical racks, which should not be paired with spur gears and helical gears; the tooth profile of the rack is a straight line rather than an involute (for the tooth surface, it is a plane) , which is equivalent to an infinite cylindrical gear with an indexing circle radius.

.The accuracy level of the rack and pinion

The national standard specifies 13 precision grades for gear pairs for gears. They are represented by Arabic numerals 0, 1, 2, ..., 12 respectively, of which level 0 has the highest accuracy, the rest of the levels decrease in turn, and level 12 has the lowest accuracy. The precision grades of the two gears in the gear pair are generally the same grade, but different grades are also allowed. At this time, the accuracy grade of the gear pair should be determined according to the one with the lower precision.

Among the 13 precision grades, the current processing technology level and measurement methods of 0, 1, and 2 precision are still difficult to promote and need to be further developed. Grade 6 is the basic grade and is also a commonly used grade in design. Gear hobbing, gear shaping, etc. are commonly used. The processing method can be achieved for a long time, and it can be measured with general measuring instruments. We generally select grades 6-8 in non-standard applications.

                                                           

Rack and pinion drive(图1)


.Selection, installation and lubrication of rack and pinion

1. Selection of rack and pinion: The modulus is a numerical value indicating the size of the tooth shape of the gear. Only when the modulus and pressure angle of the two gears are the same, the adhesive transmission can be performed.

m=d/z where d is the diameter of the reference circle; z is the number of teeth. The larger the module, the stronger the load capacity. Commonly used modules: 0.5, 0.8, 1.0, 1.5, 2.0, 2.5, 3.0; According to the actual application, the load force * reference circle radius * safety factor should be less than the allowable transmission force.

Here, by the way, the diameter of the reference circle, that is, the diameter of the index circle, affects the moving speed. The specific calculation formula is:

 w=2 Π n/60

 v=wr

Where w is the angular velocity, n is the rotational speed, the unit is r/min; r is the radius of the index circle.

In practical applications, we usually choose helical teeth. Regarding the comparison between straight teeth and helical teeth, helical teeth have the following differences:

 

a. The operation is stable and the noise is low. Since only a part of each tooth surface of the helical gear is engaged in the meshing process, or it is understood that each tooth is gradually engaged in the meshing, and no large vibration will be generated, so the noise is low.

b. High bearing capacity, helical gears with the same module width and the same width are stronger than spur gears, because the effective tooth width of helical gears is larger in this case.

c. Due to more meshing contact surfaces, the accuracy of helical teeth is generally better than that of straight teeth of the same grade. d. Because the helical gear has left-handed and right-handed, the direction must be determined when matching with the rack. Generally, the left-handed gear is matched with the right-handed rack.

e. The helix angle is a unique feature of the helical gear. Generally speaking, the helix angle of the helical gear we usually refer to refers to the helix angle on the indexing cylindrical surface. The larger the helix angle, the greater the degree of coincidence, which is more conducive to smooth movement and noise reduction. Everything is two-sided. Although increasing the helix angle brings many advantages, the axial force generated during work also increases, so the size should depend on the quality requirements and machining accuracy of the work. Generally, take 8-25 if it is correct. When there are special requirements for noise, the larger value can be taken according to the situation.

2. Installation of rack and pinion: For long-distance transmission, the rack must be installed with the gear gauge when it is installed in the segment. In particular, rack suppliers generally leave two 7 holes at both ends. The purpose is to prevent the rack from moving in the later stage. I did not use the actual distribution pin holes in the actual application, because the rack It will wear out, and the accuracy will not be achieved in the later stage, which is not easy to debug. For gear installation, be sure to do the tensioning mechanism.

3. Lubrication and dust prevention of gear racks: In the long-term operation of the rack and pinion, the accidental fall of foreign objects and the lack of lubrication will cause the wear of the gears. Therefore, the dustproof and lubrication of the rack and pinion should be done well. The commonly used dust-proof method is the sheet metal cover. Pay attention to the resilience of the sheet metal here. The adjacent shields should be connected to the sheet metal. At least the appearance of the products designed by yourself should be decent. For lubrication, we need to do a few things:

a. Select the appropriate oil pump, choose the appropriate oil pump according to the type of grease, the gear rack does not need to be filled with oil all the time, and choose different oil filling cycles according to the different grease;

b. Choose the appropriate cotton wheel to avoid tooth profile mismatch;


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