Project Decomposition

We decomposed our project into 7 major components: load application, Load Structure, log supports, Force Measurement, deflection measurements, Signal voltage measurement, and the trailer. 


Load Application and Structure

The direction in which the center load is applied must be chosen, because different orientations
 will greatly affect the overall design. It was decided that the two most practical configurations were vertical and horizontal loading. The figure to the right shows these two different loading orientations. The side load configuration would require an extra support system to help center the load on the log once it is in the machine. The only real advantage to loading from the side is that a log could be loaded from directly overhead into the machine whereas the vertical loading configuration would not allow for that.

Since this project is meant to be a proof of concept, it was decided that the vertical loading configuration is the most practical for us.                                                                                                                                         
loading orientations

For vertical loading, two different conceptual designs were developed through brainstorming
during team meetings.In the design illustrated on the right of the  Figure, the ram applying the load would be inside both of the square tubes, and the tubes would telescope while the rectangular tube off to the side would house the load cell. The load cell would have a piece bolted to it that would contact the log. The design on the left in the Figure is much simpler. The ram is directly fixed to a fixed beam, so the only moving part is the ram and load cell.

The design on the left is simpler and more rigid, so it was chosen as the better solution for this
Loading Design

We explored two different methods of applying the load to the log. We explored linear actuators and hydraulic systems. The linear actuator is a mechanical drive that uses a ball screw that is driven by a small electric motor. It provides very smooth, steady loading with an easily adjustable speed. The downside of this option is that it is very expensive and would take up the majority of our budget. Our other option is to use a hydraulic ram to apply the load and create a small hydraulic system to run this ram. This option also provides smooth steady loading, but is harder to adjust, and is also more complicated to set up.

A hydraulic system was chosen because of its flexibility of design to meet our needs and the prohibitive cost of the other option. 

Log supports

The foundation for the supports contacting the log must be much more rigid than the log itself, so that deflection of the log can be accurately measured. It was decided that a continuous length of I-beam would be the best solution. Structural I-beams are designed specifically for bending applications; stiffness and strength is maximized while weight is minimized. It is important to keep weight low since the apparatus must be portable. The I-beam was chosen by specifying that it must be ten times stiffer than the stiffest log to be tested. The lightest I-beam that met or exceeded the desired stiffness was chosen.

The way that the contacts interact with, and are adjusted along the I-beam, are taken care of by the base plate. We came up with a simple c shape that will wrap around the flange of the I-Beam. In order to hold the contacts in place, a hole will be drilled through the top and bottom of the contact plate, along with the flange of the I-beam. A pin will line up these holes and keep the contact stationary for testing. Holes will be made in the I-beams flange at set intervals along the length of the beam to allow the contacts to be adjusted for different sizes of logs.

Our first idea was using a rectangular v-shaped contact. The log could be placed anywhere on
the contact and it would center itself. However the inner edge of the contact is very sharp. This sharp edge, with a large enough load, could cause a high contact stress that could notch the log, these notches could introduce error into our deflection measurement.                                             

v support

Our second idea was to use an hour-glass shaped support. This support would be constructed from a
round solid rod that is lathed down into an hour glass shape. The hourglass shape incorporates the Vshape which will center the log. Also, due to the rounded edges it will have a lower contact stress than the rectangular V-Shape support. The lower contact stress will reduce the chance of creating notches.                                                            

v support

Force Measurement

We initially considered several load cells for use in our mechanism. The load cells that we looked at had different shapes and were selected to match our different loading designs.

load cell

deflection measurements

The first option we considered to measure the deflection of the log was a laser measurement device. For a long time we considered this to be our best option, we looked at companies such as Acuity and Keyence. As more research was done, problems began to arise that would make using a laser very complex. These problems included cost and durability. We received quotes on laser prices, and found that the least expensive of these devices cost approximately three times more expensive than any of our other measurement options. This led us to research other options more extensively; we did not want to spend that much of our budget on one component of the project.

Another option that our team looked into was a linear potentiometer. This is a proven product that we could easily integrate into our design. Our team has a good understanding of how this device works. A data acquisition device is already needed by our load cell and a potentiometer could easily be connected into that. There were a lot of benefits to this option; however, there were disadvantages as well.

While researching our other options, we found an ultrasonic measure device. This device gave us many of the benefits of the other two methods, while eliminating several of their problems. An ultrasonic device gave us answers for location, accuracy, durability, and simplicity

Signal voltage measurement

To get data from the load cell and ultrasonic sensor, we need a data acquisition device or DAQ for short.
We looked into two options, both from National Instruments.