Measurement of the mass properties of rigid bodies by means of multi-filar pendulums – Influence of test rig flexibility

The InTenso+ system has been developed at Politecnico di Milano (Technical University of Milan) for the measurement of the centre of gravity location and of the inertia tensor of vehicles and their components (such as gearboxes and engines). The test rig is basically a multi-bar pendulum carrying the body under investigation and oscillating from well-known initial conditions. By means of a proper mathematical procedure, the mass properties of the body are accurately measured within a very short time. The InTenso+ System has been employed for a number of measurements of the mass properties of road vehicles. In this paper, the measured data are collected and analyzed. Formulas for the estimation of the mass properties (mass, centre of gravity location and inertia tensor) from easily accessible vehicle data are proposed and tested against the measured values. It is confirmed that the mass properties coming from the considered estimations are useless if accurate simulations of the dynamic behavior of a vehicle have to be performed.

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A New Test Rig for Measuring the Inertia Properties of Vehicles and Their Subsystems

Design Engineering ◽

10.1115/imece2004-60903 ◽

2004 ◽

Cited By ~ 2

Author(s):

Giorgio Previati ◽

Giampiero Mastinu ◽

Massimiliano Gobbi ◽

Carlo Piccardi ◽

Luca Bolzoni ◽

...

Keyword(s):

Numerical Procedure ◽

Accurate Method ◽

The Body ◽

Inertia Tensor ◽

Ground Vehicles ◽

Test Rig ◽

Mass Properties ◽

Good Measurement ◽

Recorded Data ◽

Inertia Properties

The aim of the paper is to present the latest issues of a simple and accurate method (and related test-rig) for the measurement of the mass properties of ground vehicles and their subsystems. The method requires 1) to measure the weight and the center of gravity location of the body under investigation, 2) to make the body swing in a rather complex way in the space, 3) to record the swinging motion, 4) to identify the inertia tensor components by means of a proper numerical procedure, based both on a non-linear mathematical model of the system which carries the body and on the recorded data. The carrying system is actually a three or four-bar pendulum. A convenient configuration of the pendulum in order to obtain a good measurement accuracy is derived. A validation of the measuring procedure is presented. The measurement error on the main diagonal components of the inertia tensor is less than 1%. The rig is being used to measure the inertia tensor of a number of road vehicles and engines/gearboxes.

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Effect of the Deformation of the Supporting Structure on the Measurement of the Inertia Properties of Vehicles

Volume 3: 18th International Conference on Advanced Vehicle Technologies; 13th International Conference on Design Education; 9th Frontiers in Biomedical Devices ◽

10.1115/detc2016-59823 ◽

2016 ◽

Author(s):

Giorgio Previati ◽

Massimiliano Gobbi ◽

Federico Ballo

Keyword(s):

Mathematical Model ◽

Theoretical Analysis ◽

Rigid Bodies ◽

The Body ◽

Measuring System ◽

Test Rig ◽

Fem Model ◽

Mathematical Procedure ◽

Centre Of Gravity ◽

Inertia Properties

In the measurement of the inertia properties of rigid bodies (mass, centre of gravity location and inertia tensor) the structures carrying the body under test are usually considered to be rigid. This assumption is less and less satisfied as the dimensions of the body grow. Consequently, the forces exchanged between the body and the structures can be large enough to deform the structure and affect the measurement, especially the location of the centre of gravity. In this paper, with special reference to the InTenso+ Measuring System of the Politecnico di Milano, the effects of the deformation of the test rig structure when measuring large bodies is investigated. A theoretical analysis is performed by using a flexible multibody mathematical model of the test rig. The deformation of the test rig is deeply investigated by a dedicated FEM model. The results of the theoretical analysis are then validated by measuring the inertia properties of a light truck. It turns out that the deformation of the test rig can actually affect the measurement. This deformation can be compensated by a proper mathematical procedure. The method can, consequently, be employed also for very large bodies for which the construction of a sufficiently rigid structure as to neglect its deformation is practically impossible.

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Improved Measurement Method for the Identification of the Centre of Gravity Location and of the Inertia Tensor of Rigid Bodies

Volume 5: 13th Design for Manufacturability and the Lifecycle Conference; 5th Symposium on International Design and Design Education; 10th International Conference on Advanced Vehicle and Tire Technologies ◽

10.1115/detc2008-49830 ◽

2008 ◽

Author(s):

G. Previati ◽

M. Gobbi ◽

G. Mastinu

Keyword(s):

Rigid Bodies ◽

The Body ◽

Inertia Tensor ◽

Testing Time ◽

Crucial Importance ◽

Commercial Development ◽

Centre Of Gravity ◽

Mass Properties ◽

Inertia Properties ◽

Complex Mechanical Systems

The knowledge of the inertia properties of rigid bodies is of crucial importance for the correct simulation of complex mechanical systems. For this purpose at the Politecnico di Milano (Technical university of Milan) a series of test rigs have been constructed for the measurement of mass, centre of gravity location and inertia tensor of rigid bodies with masses ranging from 50 to 3500 kg. The test rigs are basically three or four bar pendulums carrying the body under investigation. The body is made to rotate around three axes passing nearby the body centre of gravity and the resulting highly non linear motion is recorded. A mathematical model simulating the motion of the body carried by the pendulum is used to identify the full inertia tensor by minimising the error between the computed and measured data. These test rigs are currently used for the identification of the mass properties of different cars, light farm tractors, engines, gearboxes and satellites. In this paper a new implementation of these test rigs is shown. By redesigning the instrumentation setup and with a new mathematical procedure for the identification, the test rigs can be used to identify the centre of gravity location and the inertia tensor with a single experimental test. In the new configuration the test rigs require a very short testing time and they are suitable for commercial development.

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