Chapter 10 MICROSTEPPING

Microstepping is an electronic control technique that propotions the current in a step motor’s windings to provide additional intermediate positions between poles. Produces smooth rotation over a wide speed range and high positional resolution.

Microstepping is a way of moving the stator flux of a stepper more smoothly than in full- or half-step drive modes. This results in less vibration, and makes noiseless stepping possible

down to 0ÊHz. It also makes smaller step angles and better positioning possible.

There are a lot of different microstepping modes, with step lengths from 1⁄3-full-step down to 1⁄32-fullstep or even less. Theoretically it is possible to use non-integer fractions of a full-step, but this is often impractical.

Microstepping is a way of moving the stator flux of a stepper more smoothly than in full- or half-step drive modes. This results in less vibration, and makes noiseless stepping possible

down to 0 Hz. It also makes smaller step angles and better positioning possible. There are a lot of different microstepping modes, with step lengths from 1⁄3-full-step down to 1⁄32-fullstep or even less. Theoretically it is possible to use non-integer fractions of a full-step, but this is often impractical.

T=T_H × sin(f_s - f_r)

where f_s and f_r  are given in electrical degrees.

The relationship between electrical and mechanical angles is given by the formula:

fel = (n¸4) ´ fmech

where n is the number of full-steps per revolution.

Chapter 9 ELECTRIC CLUTCH

Electric cluches are used to :

•  Engage very large motors to their loads after  the motor have reached running speeds.

• Provide smooth starts for operations in which the material being processed might be damage by abrupt starts.

• Start high- inertia loads when starting may be difficult for motor that is sized to handle only the running load.

In general an electric clutch consists of an electromagnet disc and an armature disc. When disengaged, the clutch couples the two together, allowing both to rotate. A magnetic field is generated as soon as current flows through the electromagnet disc. This draws the armature disc into direct contact with the magnet.  The electromagnet disc is faced with friction material to provide positive engagement between the two discs. Engage and disengage motions are signaled by a switch or sensor.

The electric clutch serves two functions in the operation of the mower. In addition to starting and stopping the power flow to the cutter blades, the clutch also acts as a brake to assist in stopping blade rotation when the PTO is switched off. When energized, the magnetic coil in the clutch pulls the armature into contact with the rotor, which is attached to the engine crankshaft. The armature begins to rotate, turning the attached pulley, to drive the mower blades. 

When the voltage is turned off, the magnet releases the armature. The armature is pulled against the brake cover by the armature springs. The pulley is quickly stopped by the brake, stopping the rotation of the mower blades. When a machine is new or after a clutch has been replaced, it needs to be burnished. Burnishing the clutch helps mate the surfaces of the rotor and armature. When burnishing a clutch, the engine should be run at ¾ throttle. Then engage and disengage the PTO switch approximately 50 times. Never perform the burnishing procedure while cutting grass.

Chapter 8 CONTACTOR

Contactor is a kind of switch or contact that works with the help of electricity and magnetism is able to serve the electric load current is relatively large. Magnet Contactor  is a work based on the electromagnetic switch is used to open and connect the electrical circuit (load). Magnet Contactor is working to revamp the contact Normally Open contact (NO) and Normally Closed (NC).

The Principle of Contactor

When the coil (coil) get a voltage or current is given, then the current flow in the coil will produce a fluk flow in the core. The different pole that occurs between the anchor and the anchor and resulted in the iron core of iron core pull interesting. At the time the anchor are attracted by the iron core then the contacts will operate a detachable coil voltage. When, the magnetic power will be lost and the anchor will be back in its original position due to the encouragement of a spring contact unit itself is also back in its normal position either connect or disconnect.