Unit 4: Electromechanical drive systems An Introduction to Mechanical Engineering: Part Two Electromechanical drive systems Learning summary By the end of this chapter you should have learnt about: Characteristics of loads Linear and rotary inertia Geared systems Tangentially driven loads Steady-state characteristics of loads Modifying steady-state characteristics of a load using a transmission Sources of mechanical power and their characteristics Direct current motors and their characteristics

Unit 4: Electromechanical drive systems An Introduction to Mechanical Engineering: Part Two Electromechanical drive systems Learning summary Rectified supplies for dc motors Inverter-fed induction motors and their characteristics Other sources of power: pneumatics and hydraulics Steady-state operating points and matching of loads to power sources.

Unit 4: Electromechanical drive systems An Introduction to Mechanical Engineering: Part Two 4.3 Linear and rotary inertia – key points By the end of this section you should have learnt: the similarities and differences between linear and rotational inertias and how they are analysed the concept of moment of inertia how to calculate moment of inertia for simple components made up of cylinders and tubes.

4.4 Geared systems – key points By the end of this section you should have learnt: the concept of a gear ratio how to relate angular velocities, angular accelerations and torques between input and output shafts of a geared system (or other system involving belts, friction drives etc.) the concept of ‘referred inertia’ the effect of inefficiency on the transmission of torque and on the apparent value of referred inertia. Unit 4: Electromechanical drive systems An Introduction to Mechanical Engineering: Part Two

4.5 Tangentially driven loads – key points By the end of this section you should have learnt: how to calculate the referred inertia of a tangentially driven system the inertia behaviour of screw-driven systems. Unit 4: Electromechanical drive systems An Introduction to Mechanical Engineering: Part Two

4.6 Steady-state characteristics of loads – key points By the end of this section you should have learnt: the different contributions to steady-state running characteristics of loads how to express these different contributions to the load characteristics in the form of a mathematical expression, both for linear and rotational motion that friction can have a beneficial role in some situations as well as having a detrimental effect on efficiency in other situations. Unit 4: Electromechanical drive systems An Introduction to Mechanical Engineering: Part Two

4.7 Modifying steady-state characteristics of a load using a transmission – key points By the end of this section you should have learnt: how to refer the torque–speed characteristics of a load to the input shaft of a transmission system in order to obtain the characteristics observed by the mechanical power source driving it that a transmission will affect the combination of torque and speed required to drive a load but will not help to overcome a shortfall in the power available for providing the drive. Unit 4: Electromechanical drive systems An Introduction to Mechanical Engineering: Part Two

4.8 Sources of mechanical power and their characteristics – key points By the end of this section you should have learnt: the different types of mechanical power sources used within drive systems the meaning of a torque–speed–SFC diagram for an internal combustion engine, and in particular understand the implications of its main features. Unit 4: Electromechanical drive systems An Introduction to Mechanical Engineering: Part Two

4.9 Direct current motors and their characteristics – key points By the end of this section you should have learnt: the operation of dc motors how to derive the general torque equation the different forms of dc motor why the shunt motor produces virtually constant speed how to vary the speed of a shunt motor the characteristics of a series motor how to control the speed of a series motor why the speed of a separately excited motor is proportional to the armature voltage. Unit 4: Electromechanical drive systems An Introduction to Mechanical Engineering: Part Two

4.10 Rectified supplies for dc motors – key points By the end of this section you should have learnt: how to draw the current and voltage waveforms for both diode and thyristor bridge rectifiers with an inductive load how to derive the dc output voltage for diode and thyristor bridge rectifiers with an inductive load how to calculate the speed of a separately excited dc motor supplied via bridge rectifiers. Unit 4: Electromechanical drive systems An Introduction to Mechanical Engineering: Part Two

4.11 Inverter-fed induction motors and their characteristics – key points By the end of this section you should have learnt: the principles of operation of an induction motor the operation of a simple inverter the principles of pulse width modulation induction motor torque is proportional to the applied voltage divided by frequency (V p /f ) at frequencies above ‘base speed’, the torque falls as the frequency increases approximately linear torque–speed characteristics of induction motors can be obtained for relatively low values of slip. Unit 4: Electromechanical drive systems An Introduction to Mechanical Engineering: Part Two

4.12 Other sources of power – key points By the end of this section you should have learnt: the similarities and differences between pneumatic and hydraulic systems why pneumatic or hydraulic actuators might be used in preference to electric motors the ancillary equipment needed to power pneumatic and hydraulic systems how hydraulics can be used to provide a variable-ratio drive the cost and energy-efficiency issues associated with pneumatic power and compressed air. Unit 4: Electromechanical drive systems An Introduction to Mechanical Engineering: Part Two

4.13 Steady-state operating points and matching loads of power to sources – key points By the end of this section you should have learnt: how mechanical power sources and loads interact how a transmission system may be used to match the power source to the load to calculate the combination of torque and speed at which a load and power source will operate under steady-state conditions the function of a clutch with particular reference to starting a mechanical load from rest why some sources of mechanical power are better suited to starting of loads than others. Unit 4: Electromechanical drive systems An Introduction to Mechanical Engineering: Part Two