Advantages offrictionless guideways
a. High stiffness
b. Frictionless
c. No stick-slip
d. Large damping capability
e. Better heat dissipation and hence less thermal distortion
f. Longer life.Disadvantages
a. High cost
b. Leakage problems
c. Difficultly in assembling
guide way and the slide separated by a of high compressed air. These guide ways are also called Aero static guide ways. Because of thek low stiffness characteristic they are used only in positioning applications. Such as Co-ordinate measuring machine (CMM)
Motors
Motors are rotary actuators which make rotational movement when external energy is applied to it. If the external energy given is electrical energy then it is called electric motor. Electric motors are electromechanical devices which converts electrical energy into mechanical energy. Electric motors are the most common actuators used in majority of the mechanical system where motion and force are involved.
Electric motors can be classified based on,
a. its functionality such as torque motor, gear motor, servomotor etc.
b. the type of current used i.e., d.c motors and a.c motors.
The basic principles involved in the action of a motor are,
a. A force F is exerted on a conductor of length L carrying a current /, placed in a magnetic field of flux density B at right angles to the conductor. The force so exerted is given by F = B1L. Fig. 5.40.
DC MOTORS
Principle: A loop of coil carrying current free to rotate, when placed in a field of permanent magne; is acted upon by forces on its sides at right angles to the field, rotates by 90°. Iftherototiw were to be continued the direction of current flowing through the coil is to be reversed. Fig. 5.42. In conventional d.c motors, coils of wire aremounted in slots provided on a cylinder of magnetic material called the armature. The armature is mounted on bearings in a magnetic field produced by field poles. In the fig. 5.43 the magnetic field is produced by the current carried by the field coil. The end of each coil is connected to the next segment of the segmented ring called commutator which delivers current and controls its direction into the armature coil. Solid brushes provide stationary electrical contact to the moving commutator conducting segments. (Brushes in early motors consisted by bristles of copper wire flexed against the commutator and hence the term brush). Brushes are usually made out of conducting solid graphite which provide large contact area, spring loaded for ensuring continual contact and self lubricating. In the air gap between the rotor and the stator the magnetic fields interact. As the armature rotates, the commutator reverses the direction of current in each coil as it moves between the field poles.