=Paper= {{Paper |id=Vol-1852/p10 |storemode=property |title=Development of a test bench for calibration of load moment limiter used in mobile crane |pdfUrl=https://ceur-ws.org/Vol-1852/p10.pdf |volume=Vol-1852 |authors=Giovanni Garaffo,Regina Giorlando,Renato Muscarello }} ==Development of a test bench for calibration of load moment limiter used in mobile crane== https://ceur-ws.org/Vol-1852/p10.pdf

Development of a test bench for calibration of load
moment limiter used in mobile crane
Giovanni Garaffo, Regina Giorlando, Renato Muscarello
Department of Electrical, Electronics, and Informatics Engineering
University of Catania (Italy)
email: muscarello@inwind.it

Abstract—The calibration and setting of mobile crane load
moment limiters require a series of lifting tests. To shorten
and improve these tests, a test bench strategy simulated the
validation of the load limiters. Costs were also reduced regarding
human resources, instrumentation and materials consumption.
The prototype of the test bench simulator grew from postponing
building site calibration to processing a numerical model to
acquire a vast range of data on real cranes. The test bench
simulations reliably replicate load limiter calibration in the
laboratory and eliminate setting times on the building site.
Index Terms—Load moment limiter; Lifting tests; Mobile
crane; Test bench simulator; Stability.

I. I NTRODUCTION
Nowadays, the development of effective test benches to
determine the limits of stability and of resistance to mechanical Fig. 1. G&C 45ATL mobile crane scheme.
systems is increasingly used. Both for very small systems [1],
[2], [3], which for large structures and industrial plants the use
of test benches can provide valuable and useful information Processing a numerical model which provides the security
[4], [5]. Processing a numerical model to verify the stability of system with all the necessary data for calibration requires it to
a mobile crane requires formulating the correlations between be referenced to an actual mobile crane, in this case a G&C
the load raised by the crane and the relative forces on the 45 ATL. A preliminary on-site analysis was carried out to
hydraulic jack [6], [7], [8]. By means of a load diagram and acquire the characteristics of the crane’s geometry, its fixed
crane lift-capacity tables those correlations can be calculated and moving parts. Using a digital photogrammetry technique
[9], [10], [11]. acquisition as described in [17], [18], [19], [20], [21] all 3D
Among mechanical systems simulation techniques [12], geometries were detected.
[13], [14], [15], [16], the test bench simulation strategy to This data together with data from the cranes lift capacity
the calibration and setting of the sensors and limiters [9] is tables helped define the numerical model to apply to the test
the most effective and efficient. bench and load moment limiter.
The model should list the maximum loads the crane can
lift safely in all its varying operational configurations relating II. P ROCESSING A N UMERICAL M ODEL TO T EST
to boom inclination and telescopic extension, any manual S TABILITY
extensions (with main load block) and with various sized JIBs
and considering if the crane operates with a raised boom or a To define the geometric parameters after the on-site mea-
winch. surements, we drew a 2-dimensional diagram of the crane from
Usually, the maximum loads at which the load moment which, referring to the booms rotational axis, we obtained
limiter intervenes with a pre-alarm or alarm and subsequent the hydraulic jack attachment distances, the boom lengths,
shut-down are worked out from the lift capacity tables. the centre of gravity distances of each boom section with the
The test bench simulator is a scale-model of the cranes boom closed, the characteristic angles of the raised boom and
main orientations and so studying a numerical model to apply hydraulic jack, and the distances of the fifth wheel centre and
electronically to a test bench and load moment limiter makes the booms centre of gravity.
it a requirement to know about the stability and any possible The model provides the correlations between the forces
over-loading. acting on the hydraulic jack lifting the arm, the hydraulic
liquid pressure and the lifted load. To calculate the static
Copyright © 2017 held by the authors. equilibrium, the booms centre of gravity is needed as well

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Fig. 2. Non-extended boom’ configuration.

as those of the booms telescopic sections ( G1 , G2 , G3 , G4 Fig. 3. Maximum strain on the resistant bracket.
in Fig. 2).
These help calculate the moments of force lifted
(P1 , P2 , P3 and P4 ) by a single section rolled around the
(Q + PgJIB )RJIB
boom’s hinge O. This is the ’non-extended boom’ configu- Fm = + Fm2
ration. La (sinβcosγ − cosβsinγ)
The terms Lgn for nos. 1, 2, 3, and 4 are the distances of where
the centre of gravity Gn from hinge O of the un-extended
boom (Fig. 2). Pg is the force hanging from the main load P4 i
1 bPi × (LGb − n tanα)cosα
block including the weights of various accessories and Q is Fm2 = ...
La (sinβcosγ − cosβsinγ)
the cranes capacity.
Having studied the mobile crane’s geometry, and consider- +PJIB × bR4 + (LGJIB × cos(α − θJIB )c
...
ing the centre of gravity of the hanging weight, the equilibrium La (sinβcosγ − cosβsinγ)
equation of the forces acting in the system and the distance R By reading the hydraulic pressures of the jack with the boom
from the ground to the fifth wheel centre, a formula is obtained extended, the force (Fm ) is obtained and then by inverting the
which expresses the restraining force Fm of the hydraulic jack previous formulae we obtain the capacity values (Q) even with
in the ’non-extended boom’ configuration. JIB configurations.
These formulae are then applied to a spreadsheet subdivided
(Q + Pg )R
Fm = + Fm1 into two sheets: the first calculates the force of the extended
La (sinβcosγ − cosβsinγ) boom (and consequently the jacks hydraulic pressure) knowing
where the geometric configuration and the lifted weight; the second
calculates the inverted scenario: from the hydraulic pressure
(P1 (LG1 − n tanα) + P2 (LG2 − n tanα) of the extended boom for a given geometric configuration we
Fm1 = + can obtain the lifted weight. Thus, we can compare and verify
La (sinβcosγ − cosβsinγ)
the results from the numerical model with the load capacity
(P3 (LG3 − n tanα) + P4 (LG4 − n tanα))cosα
+ limits and the cranes security parameters in the load capacity
La (sinβcosγ − cosβsinγ)
tables and the load diagram.
Similarly for the ’non-extended boom’ configuration, we
calculated the formulae to obtain Fm for the configurations III. T EST B ENCH P ROJECT
of the booms 1st, 2nd and 3rd sections extended. Then, we The test bench was of a suitable size to accommodate all
report thee general formulae as functions of the crane’s lifted the components to simulate an operational crane. To do this,
loads and the extended boom’s inclination: we calculated the operational stresses and strains considering
the total vertical loads (lifted weights + boom + accessories),
P4 the horizontal tensile stress with a maximum force of 20 tons
(Q + Pg )R + 1 Pi × (LiGb − n tanα) cosα
Fm = resulting from the stems force on the resistant bracket applied
La (sinβcosγ − cosβsinγ) to two opposite nodes with respect to its centre line on the
We also included various JIB lengths. Taking into account HEA girder; we also considered the moments applied to the
JIB weight (PJIB) and the weight of the main load block with HEA 240 support girder (at the above-mentioned nodes) as a
its various accessories (PgJIB) we arrived at the following: result of the maximum weight applied to the resistant bracket

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Fig. 4. 3D drawing of test bench Fig. 6. HEA 240 support girder.

Fig. 5. Longitudinal section of assembled test bench.
Fig. 7. Supporting steel panel.

with a 125 mm boom. As a function of the maximum force
(20 ton) and the moments (2.5 ton/m), we then calculated the on the actual machine), we devised some cup-shaped elastic
most suitable size for the resistant bracket (Fig. 3) (the forced components opportunely wrapped according to the maximum
load of 20 t is distributed on the impact area of the load cell loads anticipated for each test.
mounted on the circuit). A ’cup’ houses the ’cup-shaped springs’ which are com-
Given the large forces on the resistant bracket, it was pressed by the stem of the hydraulic cylinder.
made with an L profile, stiffening beads and a thickness On the lower cross-members and the perimeter stays beneath
of 30 mm. Analytical verifications were performed also by the test bench a steel panel (Fig. 7) is bolted to which the
means thermocamera (as described in [22]) to verify the small other test bench components are fixed, the layout of which is
deformation (< 0.1 mm). Then we sized up the threaded described in Fig. 8.
components required to attach the other plates to the HEA
A. Hydraulic Circuit
240 support girder: M24 8.8 bolts. The HEA 240 steel section
was measured as 12 mm thick at the accessory bolt holes. The design of the hydraulic circuit (Fig. 9) is crucial in
Fig. 4 shows the test benchs metal structure including all simulating the hydraulic jack which lifts the crane’s boom.
the useful accessories mounted on the hydraulic cylinder like It must replicate all the operational modes of boom lifting,
the L-bracket which supports the cylinder head and load stopping and lowering. It was sized up on the following values:
transmission resulting from the cylinder stem on the resistant • maximum operating pressure: 200 bar
bracket. • maximum force: 20 tons
Fig. 5 shows the HEA 240 support girders for the bracket. The force developed by the hydraulic cylinder stem is
To read the load applied to the load cell even as the cylinder measured by an opposing compressible load cell. It works by
stem of the test bench withdraws (when the boom lowers replicating the force developed from lifting the load (raised

61
developed through a system of data acquisition. On board
some drum is present an inclinometer that produces in exit
an electric signal that provide the inclination to which the
same is submitted. Besides, an electric capstan simulates the
maneuvers of it prolongs some arm dragging the electric
cable ultraflexible of the cable wrap. Such device of lifting
is positioned in such way by to assure the drag of the cable
ultraflexible, climbed on with horizontal draught in position
contrasted to the cable wrap.

C. Pressure Transducers
Climbed on in the rooms of exit and reentry of the hydraulic
jack to double effect: they have the function to measure,
turning her into electric signal, the pressures in the aforesaid
rooms from which, known the dimensional characteristics of
cylinder and stem of the hydraulic jack the strengths of lifting
(such values of strength will be compared with the values
measured from the cell of load, this is made necessary with the
Fig. 8. Lower level component layout. purpose to proceed to the calibration of the system of measure
and with the purpose to have a continuous control on mottos
values) can be drawn. The simulation with the hydraulic circuit
of the crane happens to parity of pressure among bench and
wrecker, therefore the transducers of pressure on the crane and
on the bench read the same parity pressure of configuration
operational tax to the crane.

IV. C ONTROL S YSTEM IN THE T EST B ENCH
The correct operation of the test bench is verified through
a system of control, which introduces a series of sensors
that allow to connect the limiter of load to the test bench
in such way to be able to test the safety device during
the cycles of operation actions to simulate the operations
developed by a crane. The innovative part of the control system
consists in the tools of evaluation of the functional parameters
and in the implementation of the algorithms of control that
happens through the creation of a dynamic 3D model of the
system [24], [25]. The model is realized through the software
SolidWorks. Such program allows, using LabVIEW and the
form SoftMotion, to simulate the realistic movement of the
crane keeping in mind of the inactivity and the attrition.
Particularly information have cared of together of SolidWorks
Fig. 9. Hydraulic circuit diagram. in LabVIEW environment and, through the creation of aces,
with NI SoftMotion, a model of crane is created similar to
that which the limiter of load is destined.
boom). The resistance of piston movement into the cylinder The exits of the sensors simulated in SolidWorks keep in
was evaluated with a procedure similar at Sequenzia et al. mind of the mechanics, of the dynamics, of the inactivity,
[23]. of the attrition of the real system. Such measures are made
notes to control’s algorithms developed in LabVIEW and
B. Cable Wrap with Inclinometer and Electric Capstan the exits of such algorithms are again sent to the simulator
The extension and the inclination of the mechanical arm and they allow to effect the mobile parts of the modeled
of the crane are simulated through an cable wrap endowed crane verifying the execution of the desired behavior. This
with an inclinometer. The first one is constituted by a drum allows a notable advantage, both in terms of times devoted to
with rubber band of call, on which an electric cable is wound the development, and in safety terms, in how much possible
resistant flexible to traction. The drum is endowed with a errors in the phase of development of the algorithms don’t
potentiometer that transforms the number of turns effected in involve some material damage to the real system. Only after
electric signal allowing the measure of the length of cable having been “debuggati” and made a will, the algorithms are

62
configuration assigned of the crane. Following they turn back
Fig. 10. Tests in the control system - load cell: 8.5 tons. the results of the test effected with cell of load of 8.5 tons.
In Fig. 10 are illustrated the graphs related to the in relief
pressure on the low room, to the pressure of the tall room and
the values to the exit of the cell of load following the answer
of the system to a reference of 8.5 tons on the load cell.
In Fig. 11 bring him in the superior part the reference to
the course (8.5 tons) in red and the answer of the cell of load:
it results evident as the desired value is quickly reached. In
the inferior part of the figure the exit of the regulator PID is
represented in the loop of control of the cell of load instead:
it is possible to observe in the graph the glut of the action of
the PID.
The gotten answers allow to verify the goodness of the
system of acquisition and control and the goodness of the
Fig. 11. Reported diagram in the cell of load of 8.5 tons. loop of control implemented for the control of the position of
the piston. Analogous tests are finished on the loops of control
of the inclinometer and the cable wrap, with results as many
satisfactory.
implemented in fact on the card of real control connected to
the bench of test. The system of control is implemented using V. V ERIFICATION OF THE L IMITER : T EST IN THE
the card of acquisition and elaboration of the data NI USB- L ABORATORY
6216 of the National Instruments. A great advantage offered The tests of simulation on the test bench are conducted
by this device is the possibility to plan the configuration and under the operational conditions of normal activity of the
to manage the acquisition or the generation of the data through instrument of lifting and in those more serious than operation
a computer using the software LabVIEW (Laboratory Virtual of the same. In the choice of the set of test of possible errors
Instrumen-tation Engineering Workbench), an environment of of formulation of the limiter is kept in mind from the operator
development for the visual planning developed by the National verifying the goodness of the intervention of the same in to
Instruments. Such software contains a bookstore of tools for signal conditions of alarm and prealarm.
the acquisition, the analysis, the visualization and the filing of The purpose of the activity of laboratory is to avoid useless
the data. wastes of resources for the activities on the field [26], [27],
In the visual planning a textual code doesn’t exist, but for which it is necessary to face in the laboratory a series
there is a diagram that allows to plan the flow of the data of test very deepened and well articulated so that to only
in the program. The programs LabVIEW has called virtual proceed to the experimentation on the field when the results
tools because it imitate the physical tools as oscilloscope and gotten damage unequivocal confirmation on the goodness of
millimeters. It is constituted from a frontal panel and from a operation of the prototype in all the predictable operational
scheme to blocks. The frontal panel is constituted in general configurations granted for the instrument of lifting.
by commands (handle grips, pulsating and other input devices) In the Tab. I are suitable the number of simulations: ac-
and indicators (graphic, LED and other display). After having tivity is composed of three sessions of tests, every session is
built the frontal panel, the code is inserted in the scheme to constituted by seven tests that differentiate him for the type of
blocks using graphic representations of functions to check the configuration of the telescopic arm simulated of the car “Type”
objects of the frontal panel. (angle of lifting of the telescopic arm, length of the arm, ray
Different tests were performed to the purpose to verify the to center earth ralla, draught) and for the value of the load
operation of the single under-systems and the efficiency of the sustained by the wrecker that he/she is wanted to simulate.
system of control. The tests of laboratory allow to verify the The tests for the verification of the limiter of load make
ability to get, with a suitable degree of precision, a geometric reference: for the value of the load lifted by the crane to the

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