Intermittent motion mechanisms are mechanisms that convert the continuous rotation of a driving member into periodic motion and pauses of a driven member.
Examples include the transverse feed motion of a shaper's table and the film feeding motion of a movie projector. Common intermittent motion mechanisms include: ratchet mechanisms, Geneva mechanisms, linkage mechanisms, and incomplete gear mechanisms.
▲ Intermittent motion of an incomplete gear.
This involves using a gear that doesn't cover the entire circumference as the driving gear. The toothless section of the arc will not drive the driven gear, thus achieving intermittent motion.
▲ Intermittent motion of a Geneva wheel.
This mechanism consists of a grooved Geneva wheel and a pin. When the pin is inserted into the groove of the Geneva wheel, it drives the Geneva wheel to rotate; when the pin leaves the groove, the Geneva wheel stops rotating.
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Universal Joint
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A universal joint is a component that enables variable-angle power transmission. It is used in positions where the direction of the drive shaft needs to be changed. It is the "joint" component of the universal joint transmission device in an automotive drive system. A universal joint combined with a driveshaft is called a universal joint drive system.
In front-engine, rear-wheel-drive vehicles, the universal joint drive system is installed between the transmission output shaft and the drive axle final drive input shaft; while in front-engine, front-wheel-drive vehicles, the driveshaft is omitted, and the universal joint is installed between the front axle half-shaft (responsible for both drive and steering) and the wheels.
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Cam-type Intermittent Motion Mechanism
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A cam-type intermittent motion mechanism consists of a driving cam, a driven disc, and a frame. The driving cam has a curved groove or ridge with open ends on its cylindrical surface, and the driven disc has evenly distributed cylindrical pins on its end face. When the cam rotates, the curved groove or ridge actuates the cylindrical pins on the driven disc, causing the driven disc to perform intermittent motion.
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Rack and Pinion Drive
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The working principle of a rack and pinion drive is to convert the rotational motion of the gear into the reciprocating linear motion of the rack, or to convert the reciprocating linear motion of the rack into the rotational motion of the gear.
A rack and pinion mechanism consists of gears and racks. We've discussed gears in detail earlier. Racks are divided into spur racks and helical racks. The tooth profile of a rack is a straight line, not an involute (it's a plane for the tooth surface), equivalent to a cylindrical gear with an infinite pitch circle radius.
Main characteristics of racks:
(1) Because the rack tooth profile is a straight line, all points on the profile have the same pressure angle, which is equal to the inclination angle of the profile. This angle is called the tooth profile angle, with a standard value of 20°.
(2) Any straight line parallel to the addendum line has the same tooth pitch and module.
(3) A straight line parallel to the addendum line with a tooth thickness equal to the tooth space width is called the pitch line (center line), which is the baseline for calculating rack dimensions.
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Belt Drive
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Belt drive is a mechanical transmission that uses a flexible belt tensioned on a pulley to transmit motion or power. Depending on the transmission principle, there are friction belt drives, which rely on the friction between the belt and pulleys, and synchronous belt drives, which rely on the meshing of teeth on the belt and pulleys.
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Gear Transmission
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This structure is similar to a car differential, mainly composed of left and right half-shaft gears, two planetary gears, and a gear carrier.
The engine's power enters the differential via the driveshaft, directly driving the planetary gear carrier. The planetary gears then drive the left and right half-shafts, which in turn drive the left and right wheels respectively. The differential is designed to satisfy: (left half-shaft speed) + (right half-shaft speed) = 2 (planetary gear carrier speed). When the car is traveling straight, the speeds of the left and right wheels and the planetary gear carrier are equal, resulting in a balanced state. However, when the car turns, this balance is disrupted, causing the inner wheel speed to decrease and the outer wheel speed to increase.
