Worm gear transmission is composed of a worm and a worm wheel, and generally the worm is the active part. The worm gear has the same right-hand and left-hand threads, which are called right-hand and left-hand worm gears respectively. A worm is a gear with one or more helical teeth that meshes with the worm wheel to form a staggered shaft gear pair. The indexing surface can be cylindrical, conical or circular, and there are four categories of Archimedes worm, involute worm, normal straight profile worm, and tapered enveloping cylindrical worm.
Advantages of worm gear transmission.
✦ The single-stage transmission ratio is large, generally i=10~100. In the indexing mechanism for power transmission, the maximum can be over 1500.
✦ The same meshing is linear contact, which can withstand large power.
✦ Compact structure, smooth transmission, and low noise.
✦ When the lift angle of the worm is less than the equivalent friction angle between the gears, it is self-locking with counter-stroke, i.e., only the worm can drive the worm wheel, not the worm wheel.
Disadvantages of the worm gear drive.
✦With two axes perpendicular, the linear velocity of the two wheel nodes is perpendicular, so the relative sliding speed is large, easy to heat and wear.
✦Low efficiency, generally 0.7 to 0.8; worm gears with self-locking worm gears are even less efficient, generally less than 0.5.
Does a worm gear stepper motor necessarily have self-locking performance?
No, there are prerequisites. When the lead angle < friction angle, the worm gear stepper motor can be self-locking.
Usually when the gear reduction stepper motor is selected, the user must use power failure protection or brake motor, so the gear reduction motor will be selected with a brake to achieve the purpose of stopping, but does not mean absolute stop, a little inertia is still there.
What is self-locking? The concept of self-locking is that no matter how much force can not start, no matter how much inertia, as long as the work of the active part to stop running, the whole machine can brake, worm gear geared stepper motor has this self-locking performance. There is no self-locking performance for geared stepper motors, and there is reliable self-locking performance for worm gear reducers with speed ratios of 1:30 and above, and the larger the reduction ratio, the better the self-locking performance.
How to choose the reduction ratio to ensure the self-locking performance of the worm gear stepper motor?
1、Worm gear friction coefficient is 0.6, the worm gear guide angle is less than 3°29′11″ that is self-locking, and vice versa.
2、Worm gear friction coefficient is 0.7, the worm gear guide angle is less than 4°03′57″ that is self-locking, and vice versa.
3、When the friction coefficient of the worm wheel is 0.8, the lead angle of the worm is less than 4°38′39″, that is, self-locking, and vice versa.
When the lead angle of the worm is less than the equivalent friction angle between the teeth of the meshing wheel, the reduction stepper motor mechanism has self-locking, which can achieve reverse self-locking, that is, only the worm can drive the worm wheel, but not the worm wheel drive the worm. Generally in the design of heavy machinery, designers tend to use the worm gear mechanism with self-locking, because its reverse self-locking can play a very important role in safety protectio
Calculation formula of worm wheel and worm gear.
1. Transmission ratio = number of worm gear teeth ÷ number of worm head
2、Center distance = (worm wheel pitch + worm gear pitch) ÷ 2
3、Worm wheel diameter = (number of teeth + 2) × modulus
4、Worm wheel pitch=module×number of teeth
5、Worm pitch=worm outer diameter-2×module
6、Worm guide = π×module×head
7、Helix angle (guide angle) tgB=(modulus×head number)÷worm pitch
8、Worm lead=π×module×head
9、Modulus=diameter of indexing circle/number of teeth
The number of heads of worm: single-headed worm (there is only one helix on the worm, i.e. the worm turns for one week and the worm wheel turns through one tooth); double-headed worm (there are two helixes on the worm, i.e. the worm turns for one week and the worm wheel turns through two teeth).
Modulus is the size of the helix on the screw, i.e. the larger the modulus, the larger the helix on the screw.
The diameter factor is the thickness of the screw.
Modulus: The indexing circle of a gear is the benchmark for designing and calculating the dimensions of each part of the gear, and the circumference of the gear indexing circle = πd = z p, so the diameter of the indexing circle
d=z p/π
Since π is an irrational number in the above equation, it is not convenient for the positioning of the index circle as a reference. In order to facilitate calculation, manufacture and inspection, the ratio p/π is now artificially specified as some simple values, and the ratio is called modulus (module), expressed as m.
Types of worm gearing
According to the different shapes of worm, worm can be divided into cylindrical worm drive, annular worm drive and conical worm drive. Among them, the cylindrical worm drive is the most widely used.
Ordinary cylindrical worm gears are mostly cut on the lathe with a turning tool with a straight bus blade. With the variation of the tool installation position and the tool used, four types of worm gears with different tooth profiles in the cross section of the vertical axis can be obtained: involute worm gears (ZI type), Archimedes worm gears (ZA type), normal straight profile worm gears (ZN), and tapered enveloping cylindrical worm gears (ZK).
Involute worm (ZI type) - the blade plane is tangent to the worm base cylinder, and the end teeth are involute, suitable for higher speed and larger power.
Archimedean worm (type ZA) - The tooth profile perpendicular to the axis plane is Archimedean screw, and the tooth profile in the plane past the axis is straight, simple processing and low accuracy. (Axial straight profile worm gear).
Normal straight profile worm (ZN) - can be used to grind teeth with modified grinding wheel, processing is simple, often used for multi-head worm, transmission efficiency up to 0.9.
Seeing that you have a brief understanding of the transmission principle of worm gear motors, if there is anything else you would like to communicate, please contact us!
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Post time: Jan-30-2023