37552 - Mechanics of Motor Drives

Course Unit Page

Academic Year 2020/2021

Learning outcomes

Students will learn fundamental topics and methodologies for the study of problems concerning the modelling, analysis and synthesis of mechanical  transmissions and the connection between driving and operated machines.

Course contents

POWER TRANSMISSION DEVICES

1. Couplings, clutches and brakes.

− Rigid, compliant and mobile shaft couplings.

− Application: Torsional vibrations generated by a Cardan coupling.

− Positive-contact and friction mechanical clutches. Overrunning clutches (freewheels). Fluid couplings.

− Disk, drum and band mechanical brakes.

2. Power transmission devices with constant or selectable transmission ratio.

− Ordinary and planetary gear trains: transmission ratio, efficiency, external moments. Differentials.

− Application: Kinematic analysis of a planetary gearbox.

− Application: Kinematic design of the gear reducer for an electric hoist.

− Mechanical continuously-variable transmissions: variable-speed rigid-link, belt and chain drives.

3. Power transmission devices with variable transmission ratio.

− Motion laws with periodic transmission ratio. The motion law and its properties: velocity, acceleration and torque coefficients. Criteria for the choice of the displacement function: limitation of velocity, acceleration and driving torque. Qualitative comparison between displacement functions.

− Application: Displacement functions with piecewise-constant acceleration; displacement functions with trapezoidal acceleration.

− Cam mechanisms. Classification. Graphical layout of cam profiles. Kinematic and kinetostatic analyses. Pressure angle, undercutting and dimensions. Force and form joint closure: positive-motion and dual-cam mechanisms.

− Application: Kinetostatic analysis of a cam mechanism.

− Intermittent-motion mechanisms: Geneva mechanisms, indexers.

− Planar linkages. RRRR, RRRP and RRPP kinematic chains. Special positions: stationary and singular configurations. Coupler curves. Dwell mechanisms and force amplifiers. Quick-return mechanisms. Mechanisms for linear and translatory motions.

CONNECTION BETWEEN DRIVING AND OPERATED MACHINES

5. Dynamics of a single-degree-of-freedom machine.

− Equation of motion. Energetically-equivalent reduced machine. Steady-state operation. Steady-state torque-speed characteristics of driving and operating machines. Speed regulation.

6. Choice of the motor/reducer group.

− Choice of the electric motor: the thermal problem, duty cycles, influence of the start-up transient. Selection and verification of the brake. Selection and verification of the clutch. Selection and verification of the gear reducer: service factor, peak torque, radial and axial loads, bearing reactions.

− Selection and verification of gearmotors for static loads and single-speed operations. Selection and verification of gearmotors for periodic steady-state operations: criteria of maximum and root-mean-square torques. Limitation of nonuniformity: the flywheel.

7. Applications.

− Study of a start-up transient. Selection of a brake motor and analysis of the braking transient. Selection of a friction clutch and analysis of the insertion transient. Selection and verification of the gearmotor for a translating-saddle drive. Selection and verification of the gearmotor for a rotary-table drive. Selection of the gearmotor for an intermittent-motion-mechanism drive.

FUNDAMENTALS OF FLUID POWER TRANSMISSIONS

8. General principles and components.

− Fluid transmission of power. Statics and kinematics of liquids. Fundamental equations of rotary and linear hydraulic pumps and motors.

− Gear, vane and piston pumps and motors; hydraulic cylinders. Main components of hydraulic circuits.

9. Hydraulic circuits.

− Start-up transient of a hydraulic cylinder. Elementary hydraulic circuits.

− Applications: Verification of an open-chain hydrostatic transmission; selection of an elementary hydraulic drive; hydraulic drive for a lifting platform.

COMPLEMENTARY ACTIVITIES

9. Technical seminars with experts from the industry.

Readings/Bibliography

  1. LEZIONI DI MECCANICA APPLICATA ALLE MACCHINE, Parte I: Fondamenti di Meccanica delle Macchine. E. Funaioli, A. Maggiore, U. Meneghetti. Pàtron Editore, 2009 (required main text, in Italian).
  2. LEZIONI DI MECCANICA APPLICATA ALLE MACCHINE, Parte II: Elementi di Meccanica degli Azionamenti. E. Funaioli, A. Maggiore, U. Meneghetti. Pàtron Editore, 2009 (required main text, in Italian).
  3. MECHANICS OF MACHINES. W.L. Cleghorn, N. Dechev. Oxford University Press, 2016 (alternative textbook, in English).
  4. DRIVE ENGINEERING – PRACTICAL IMPLEMENTATIONS: PROJECT PLANNING OF DRIVES. Sew-Eurodrive Documentation, 2001, http://www.sew-eurodrive.com (supplementary reading for the topic "Connection between driving and operated machines").
  5. BASICS OF HYDRAULIC SYSTEMS. Qin Zhang. CRC Press, 2009 (supplementary reading for the topic "Fundamentals of fluid power transmissions").

Teaching methods

Classes are based on theoretical lectures with application examples.

Assessment methods

The integrated course MECHANICS OF MACHINES T is offered to the students of the second year of the Bachelor Degree in Mechanical Engineering (LT DM 270/04). It comprises the two units FUNDAMENTALS OF MACHINE MECHANICS T (6 credits) and MECHANICS OF DRIVES T (6 credits).

The examination of the integrated course consists of two written tests, one for each unit of the course. The first test focuses on the program of the unit Fundamentals of Machine Mechanics, whereas the second on the program of the unit Mechanics of Drives. It is highly desirable (but not strictly required) that the tests are taken in the aforementioned order. The examining committee may, at its discretion, require the student an additional oral exam. The final grade is given by the arithmetic mean of the marks obtained in the two written tests, corrected by the outcome of the oral examination (if any). Each written test is passed if the candidate achieves a mark of at least 17/30, while the overall examination is passed if the candidate obtains a grade no smaller than 18/30.

According to the University Regulations, each examination determines a positive or negative evaluation. A positive assessment involves the assignment of a numeric grade equal to or greater than 18/30. A negative assessment does not result in a numeric grade, but in a descriptor (i.e. withdrawn or rejected) reported on the examination record. The negative evaluation is not included in the student academic record and it does not affect the average score that determines her or his final degree grade. The examination, if passed with a positive outcome, cannot be repeated.

If a positive grade does not meet the expectations of a student, the latter may ask its cancellation and the repetition of the examination. The instructors of the course Mechanics of Machines T comply, in general, with the following rules:

  • a student may request the cancellation of a positive grade only within the date specified in the public communication of the examination outcome;
  • a cancelled positive grade can in no way be recovered;
  • a student may request the cancellation of a positive grade at most once.

Teaching tools

On the E-learning Platform, students may find:

- slides of the course lectures;
- exercises and application examples;
- exam problems.


Links to further information

http://www.unibo.it/docenti/marco.carricato

Office hours

See the website of Marco Carricato