About Gears a. A toothed machine part, such as a wheel or cylinder, that meshes with another toothed part to transmit motion or to change speed or direction. b. A complete assembly that performs a specific function in a larger machine. c. A transmission configuration for a specific ratio of engine to axle torque in a motor vehicle.
OR
in other words A wheel with teeth around its
rim that mesh with the teeth of another wheel to transmit motion. Gears are
used to transmit power (as in a car transmission) or change the direction of
motion in a mechanism (as in a differential axle). Fixed ratios of speed in
various parts of a machine is often established by the arrangement of gears
A belt is a loop of
flexible material used to mechanically link two or more rotating shafts, most
often parallel. Belts may be used as a source of motion, to transmit power
efficiently, or to track relative 539 movement. Belts are looped over pulleys
and may have a twist between the pulleys, and the shafts need not be parallel.
In a two pulley system, the belt can either drive the pulleys normally in one
direction (the same if on parallel shafts), or the belt may be crossed, so that
the direction of the driven shaft is reversed (the opposite direction to the
driver if on parallel shafts). As a source of motion, a conveyor belt is one
application where the belt is adapted to continuously carry a load between two points.
Belt Drive a mechanism
that transmits rotational motion from one pulley mounted on a shaft to another
by means of a belt. The belt transmits torque from the driving pulley (Figure
1) to the driven pulley by means of the forces of friction that arise between
the taut belt and the pulleys. The type of belt used determines whether the
mechanism is flat-belt, round-belt, or V-belt. A belt drive with a multiple
V-belt, which has several grooves on its inner surface, is now becoming
increasingly common. Flat and round belts, as a rule, are used singly in a
drive, while several V-belts (usually no more than eight) can be used together.
Figure 1. Diagram of a belt drive and cross sections of the various belts: (a) flat belt, (b) V-belt, (c) round belt, (d) multiple V-belt; (1) driving pulley, (2) belt, and (3) driven pulley
Flat-belt drives are simple and convenient. They permit the use of ordinary pulleys with smooth surfaces, and they can be operated at speeds as high as 40–50 m/sec and more. However, they are bulky in design and low in strength, and their tension ratio usually does not exceed 5. V-belt drives provide improved attachment of the belt to the pulleys, permit shortening of the center distances, and allow a decrease in the size of the drive and an increase in the tension ratio (up to 10-15). Round-belt drives are now rare and are used only in mechanisms of low power, such as those in sewing machines.
The advantages of belt drives are their simplicity of design, relative low cost, capacity to transmit power over significant distances (up to 15 m and more), and smooth and noiseless operation. In addition, the elastic properties of the belt and its ability to slip on the pulleys help prevent overload. The disadvantages include the short lifetime of the belts, relatively large size, heavy stress on the shafts and bearings, and variation in the tension ratio caused by the inevitable slipping of the belt.
Belts made of highly elastic,
strong synthetic materials, narrow V-belts, and timing belts are becoming
increasingly common. Belt drives are widely used in agricultural machines,
electric generators, certain machine tools, and textile machines. They are
ordinarily used for transmitting power up to 30–50 kilowatts, but there are
machines in which belt drives are used to transmit power of hundreds and even
thousands of kilowatts.
Type of Gears
Round belts
Round belts are
generally made of rubber this type of belts is generally used for light loads
Such as in a sewing machine or a vacuum cleaner.
STEPPER MOTORS
Stepper motors are
special versions of the synchronous machine, in which the rotor is a permanent
while the stator consists of a coil package. In contrast to synchronous motors,
stepper motors have a large number of poles. Motor operation requires a control
unit, stepper motors come in numerous varieties, which tend to be based on
three basic types:
- Variable reluctance (stepper) motor (VR)
- Permanent magnet stepper motor, claw – poled PM motor, tin can motor (PM)
- Hybrid stepper motor (HY)
A stepper motor (or step motor) is a brushless DC electric motor that divides a full rotation into a number of equal steps. The motor's position can then be commanded to move and hold at one of these steps without any feedback sensor (an open‐loop controller), as long as the motor is carefully sized to the application.
Frame 1:
The top electromagnet (1) is turned on, attracting the nearest teeth of the gear-shaped iron rotor. With the teeth aligned to electromagnet 1, they will be slightly offset from right electromagnet (2).
Frame 2:
The top electromagnet (1) is turned off, and the right electromagnet (2) is energized, pulling the teeth into alignment with it. This results in a rotation of 3.6° in this example.
Frame 3:
The bottom electromagnet (3) is energized; another 3.6° rotation occurs.
Frame 4:
The left electromagnet (4) is energized, rotating again by 3.6°. When the top electromagnet (1) is again enabled, the rotor will have rotated by one tooth position; since there are 25 teeth, it will take 100 steps to make a full rotation in this example. Switched reluctance motors are very large stepping motors with a reduced pole count, and generally are closed-loop commutated.
Construction:
A
stepper motor consists of the following two main parts: (I) Stator (II) Rotor
- Stator: a stepper motor contains two or three winding which are wound on the stator. Since, the windings are wound only on the stator portion of the motor hence, there is no necessity of a commentator etc. with this motor.
- Rotor: the rotor of a stepper motor is made of either a magnetic metal in the form of a toothed wheel or permanent magnets Types: on the basis of rotor construction, stepper motors may be classified into the following two main classes.
(i) Variable reluctance stepper motor (ii)
Permanent magnet stepper motor
Stepper
motor system
A
stepper motor system consists of three basic elements, often combined with some
type of user interface (host computer, PLC or dumb terminal):
- Indexers
- The indexer (or controller) is a microprocessor capable of generating step
pulses and·
direction signals for the driver. In addition, the indexer is typically
required to perform many other sophisticated command functions.
- Drivers - The driver (or amplifier) converts the indexer command signals into the power necessary to energize the motor windings. There are numerous types of drivers, with different voltage and current ratings and construction technology. Not all drivers are suitable to run all motors, so when designing a motion control system the driver selection process is critical.
- Stepper motors - The stepper motor is an electromagnetic device that converts digital pulses into mechanical shaft rotation. Advantages of step motors are low cost, high reliability, high torque at low speeds and a simple, rugged construction that operates in almost any environment. The main disadvantages in using a stepper motor is the resonance effect often exhibited at low speeds and decreasing torque with increasing speed Advantages/disadvantages of stepper motors
Advantages
- Low cost for control achieved
- High torque at startup and low speeds
- Ruggedness
- Simplicity of construction
- Can operate in an open loop control system
- Low maintenance
- Less likely to stall or slip
- Will work in any environment
- Require a dedicated control circuit
- Use more current than D.C. motors
- Torque reduces at higher speeds
