Download Report on Measurement Solutions for Angular Position of the

Report on Measurement Solutions for Angular Position of
the Slewing and Rotator applied to the Laboratory Crane
and the Komatsu Forwarder 830
Tobias Conradsson
[email protected]
Fredrik Jonsson
[email protected]
Supervisor:
Uwe Mettin
[email protected]
Table of contents
1 Project objective ..................................................................................................................3
2 Project participants ..............................................................................................................3
4 Evaluation of project objectives ...........................................................................................3
5 Problem specification ..........................................................................................................3
5.1 Slewing.........................................................................................................................4
5.1.1 Laboratory crane ....................................................................................................4
5.1.2 Komatsu Forwarder 830.........................................................................................6
5.2 Rotator..........................................................................................................................7
5.2.1 Laboratory crane ....................................................................................................7
5.2.2 Komatsu Forwarder 830.......................................................................................10
6 Conclusions.......................................................................................................................10
2
1 Project objective
The project is divided into two parts; the first one is to mount measuring devices for angular
positioning for the arm of the crane and measuring of the extraction of the telescope, for the
Komatsu Forwarder 830, and make an installation manual for this. Second part is to figure out
solution to measure slewing of the crane and rotation of the gripper; both Komatsu Forwarder
830 and laboratory crane, and mount these measuring devices as well. This report is going to
focus on the second part of the project.
2 Project participants
The supervisor of the project is Uwe Mettin, and the project group as well as project managers
are Fredrik Jonsson and Tobias Conradsson.
4 Evaluation of project objectives
The project objectives have not been achieved by 100%. Measurements where done by the
attached position sensor devices for the arm, though none were done with the measuring
devices for the rotation of the gripper and slewing of the crane. We did not mount any
measuring devices for the Komatsu Forwarder 830 either, even though the principle is the
same and only minor differences tell them apart.
The project has been finished within the desired timeframe, which was scheduled to be at
beginning of June.
5 Problem specification
When to figure out a solution for measure the angular position of gripper and tower it is not a
trivial task to make proper measuring devices, first you need to define what kind of resolution
you would like in your measurements. Second you have to choose what type of sensor you
would like to have, based on the resolution demanded. Here you have many different types of
sensors, magnetic, inductive, optical etc etc, to choose from.
The purpose of this project is not to develop a new in market working product; it is for
prototyping purpose only, which makes the product less demanding when it comes to hits and
durability. The sensitivity requirement to dirt and mud is also highly reduced at least when it
comes to the laboratory crane.
In the choice of sensor there are mainly three types of electrical interfaces, digital, analogue or
incremental. An analogue sensor has good resolution and a continuous signal, because that it
measures continuous information, making it easy to interpret. This type of sensor might be
good when one want to measure a resistance, voltage or pressure they might even be used for
rotation measurements. But they often carry allot of noise and the signal might be weak which
means that amplification is needed and then the noise is amplified as well. Digital sensors
don’t have the disadvantage of noise, and the digital devices are often much smaller than the
analogue ones. Digital sensors don’t have the same continuous measurements, they use
discrete measurements.
Capacitive sensors
Capacitive sensors basically work due to a capacitance building up between to plates (plus
charges on one plate, minus charge on the other) and the capacitance is, as well known,
depending on the distance between the plates, therefore this is mainly used to measure how
3
something is compressed or extracted. Similarly this might be used as an accelerometer as
well.
Inductive sensors
To detect magnetic fields one might use inductive sensors, this works due to a magnetic field
is causing an induced current through a coil which is then measured and evaluated. Often this
current is amplified cause of its small amplitude.
Optical sensors
Optical sensors might look very different from device to device, but basically they all work
the same, light is emitted and reflected in some way, then some time interval is measured or
number of reflected beams is calculated, this might be very precise and have very good
resolution. But instead it is very sensitive to dust and hits; if the device gets hit, there is a big
risk for the light emitting device to get disturbed as well. Therefore it is very important when
using optical measurements to surely enclose the device and make it durable not only to
protect against dust but also to absorb eventual shocks from hits.
Hall sensor
Hall sensors exist in both analog and digital form. They work in such a way that a magnetic
field outside a conductor or a semiconductor will induce a hall voltage in the conductor or
semiconductor. The hall voltage is dependent on the size of the magnetic field and therefore
you can measure the distance to a magnet. Or in the digital form you will get a signal in the
magnetic field and you will not get a signal then you are at a certain distance from the magnet.
They are quite precise and can make measurements with quite good accuracy. They do need a
plate (or other suitable device that can carry some magnets) with mounted magnets to work
and the resolution is therefore dependent on the size of the magnets and the size of the plate.
5.1 Slewing
5.1.1 Laboratory crane
Slewing is then the crane rotates around its own axis. It is possible for the crane to
rotate approximately 300 degrees around its own axis. So it can not rotate several
turns in follow. The crane can reach ten meters out from the tower where it is
mounted.
Figure 1. Sketch over the crane and how the crane can move around its own axis.
In slewing measurement the accuracy of measurement should be quite high as a
result of the length of the arm. One degree in angular movement will result in 175
mm movement in the end of the arm where the gripper is placed. The rotating part of
the tower is fastened in top of the fixed part and will not be taken apart without some
huge problems see Figure 2. There is also another thing to take care of. Even if this
4
is just a prototype and not an industrial solutions the measurement device should
work in dirty terrain and it should also handle some rain.
Figure 2. The crane seen from the side.
For the slewing measurement we choose an optical sensor that is inbuilt in a box.
From this box it goes a wire that is used for measuring. This is called draw wire box
in this report. We let this wire go around the tower of the crane and mounted that
after one turn around the tower. This is a solution that works due to the fact that the
tower will just turn 300° and not several revolutions. The draw wire box is mounted
so the wire will be in tangent with the tower, see Figure 3. This draw wire box has a
resolution of 0.3 mm.
The draw wire box will be mounted on two different cranes one is the TFE lab crane
and the other is a crane that is mounted on a komatsu forwarder. We use the same
encoders on both cranes and this will end up with a difference in resolution due to
that the size of the tower differs and the length of the crane. In Figure 3 it is possible
to see how the encoder is mounted on the TFE lab crane and Figure 4 is showing the
same thing from the side.
Figure 3. Draw wire bow mounted on TFE crane seen from above
5
Figure 4. Draw wire box mounted on TFE crane seen from side
Figure 5. Draw wire box mounted on Komatsu crane seen from above
Figure 6. This shows the Simulink block diagram for slewing encoder.
5.1.2 Komatsu Forwarder 830
For the crane to Komatsu forwarder 830 we had to change some mounting
equipment to the draw wire box this can be seen in Fig 5.
6
5.2 Rotator
5.2.1 Laboratory crane
The rotator is placed at the end of the arm, connecting it to the gripper, when it
rotates it might rotate absolutely free around its own axis (no maximum amounts of
revolutions). This it self makes it a bit different from the slewing and the same
solution applied to the slewing is not possible to use for the rotator.
The resolution that in the case of slewing was needed to be very precise might in this
case instead be much less accurate. At first we stated that the resolution for the
rotator would have to be at least 45 degrees, which is much less accurate then the
slewing, this due to the fact that it’s not that extended, and a minor fault in angle
don’t become as large error as a equally large fault in angle for the slewing. And due
to the fact that this is made for prototyping purpose only no especially good
resolution is needed for this part at the moment.
We decided to use magnetic sensor and magnets to detect angular position of the
gripper, this mostly due to expenses and the fact that it is much easier to construct
yourself. Another advantage for the magnetic solution is that the magnetic field is
not influenced when it comes to hits, unlike for example an optical solution where
the device has to be well protected.
We chose to make a plate out of aluminium and attached the magnets onto this plate.
The aluminium was chosen mostly because it doesn’t oxidize as ordinary iron does,
due to its simplicity to work with and because of the fact that we are working with
magnets, that will have their magnetic field heavily reduced by mounting them into a
ferromagnetic material. We thought that the best place for the plate to be mounted
would be right above the gripper and under the rotator.
After some testing with the magnets (specifications for magnets might be seen in
table 1) we realized that we would be able to have much better resolution than the at
least desired 45 degrees that were fist stated this due to the sensor didn’t pick up a
signal that far from the magnets when it approached the magnets slightly above and
from the side. Then we considered 10 degrees as a reasonable resolution. We also
decided that there would be good to have a reference point somewhere on the plate,
which implies that there are going to be two sensors needed for the measuring. Then
the aluminium plate was made and holes for magnets were drilled with an angle of
10 degrees separating them. There was also a hole for the reference point made at
the same line from the centre as one of the other holes but 20 mm closer to the centre
then the rest of the holes. For a complete drawing see Figure 7.
To mount the sensors a z-profile of steel was made, when to attach the sensors one
has to think about having the edge of sensors that leans towards the plate about
10mm (for nominal sensing range of 60mm, 15mm if nsr is 70mm, see Table 2)
below the edge of the steel plate, this due to that the steel is ferromagnetic and might
disturb the measuring. The z-profile is made so that the sensors might be mounted as
one pleases and sees work best, this thanks to the elongated hole and the round hole
is for mounting the z-profile with a hex bolt on top of the rotator see Figure 9.
7
A block diagram of how the signal enters the computer is shown in Figure 10
NdFeB N35
Material:
Ni-Cu-Ni
Surface
max: 263-287 kJ/m3
max. Energy Product (BH)
1170-1210 mT
Residual Flux Density (Br)
11700-12100
Gauss
80 Degree Celcius
Max. Operating Temp (Tmax)
≥ 868 kA/M
Coercive Force (Hcb)
Diameter 5mm, Height 2mm
Dimensions
9,90 € for 50 magnets (0.198 € a piece)
Price
Table 1. This shows the specifications for the magnets.
Figure 7. This is the drawing of the aluminium plate with dimensions in mm.
8
Figure 8. Shows the piece where the sensors are attached, the small hole is for
mounting the z-profile onto the gripper, and the larger elongated hole is for the
sensors.
Figure 9. This shows the gripper of the laboratory crane from above with the
attached z-profile for mounting sensors. Beneath the rotator and above the gripper
the aluminium plate might be spotted.
9
Sensor for angular position of the rotator.
Descritption:
ifm electronics
Manufacturer:
MEB3060-BPKG/PH
Type:
60mm
Nominal sensing range:
-25...75 °C
Operating temperature:
10...30 VDC
Operating voltage:
200 mA
Current rating:
Pulsed
Short-circuit protection:
Yes
Reverse polarity protection:
Yes
Overload protection
< 2.5V
Voltage drop:
< 10 mA
Current consumption:
IP 67
Protection:
469 SEK (total 938 SEK)
Price
Table 2. This shows the specifications for the sensor.
Figure 10. Shows the simulink block diagram for rotator encoder.
5.2.2 Komatsu Forwarder 830
When it comes to the real crane we did not have enough time to produce an
equivalent product, but similar solution might be applied. Differences are for
example lack of possibilities to attach the plate onto the gripper, there is not the
same amount of bolts and that might cause a problem. Besides this there shouldn’t
be much of a difference from the laboratory crane.
6 Conclusions
We think that we have chosen the best solution for the task at hand. If the purpose had been to
develop a new kind of product that would have to have been competitive on the market then
this might not have been a good solution. If this is to be a permanent equipment one might
think about building the measuring device into the rotator or tower in some way. Then the
solution might be better of with the optical sensor at least for the tower where not so large hits
might occur, at the gripper on the other hand hard bumps from trees might cause problem to
the sensor, i.e if optical solution is going to be used for the gripper as well, very good
protection and something that absorbs the shocks well is needed.
10
It has been a fun project which has given a lot of new knowledge. Even though we would
have liked to come in contact with companies outside the university some more it has been a
rewarding experience.
11