Student Projects
Force Sensing Device
by
Low Chang Weng
Lew Yeong Chee
Wong Yan Ming
Rodney Tan
UCSI University
Malaysia
Products Used:
National Instrument DAQ 6008
National Instrument LabVIEW 8.5
The Challenge:
Designing a flexible test system for measuring force using conventional spring as a case study. This test system will serve as a learning platform for those who are studying force-spring related subjects such as dynamic in the university.
The Solution:
Using National Instrument DAQ 6008 combined with the graphical features of National Instrument LabVIEW 8.5 software to design a control program for data acquisition, management and processing. By using the data acquired, these data can be processed into a graphical formula and can be convert the data directly to desired results.
Abstract
The Force Sensor is designed to test the performance of conventional spring acting as a force-sensing element. The spring-force value will be converted into voltage using a potentiometer. By using this sensor, the characteristic of the spring and it’s relationship with force can be studied thoroughly. The force will be applied to a platform that is supported by the spring. The spring will be compressed along with the potentiometer and the voltage that changes along with the potentiometer will be analyze by NI DAQ card.
Introduction:
Hooke’s Law has always been taught in the education system and was derived as “the extension of a spring is in direct proportion with the load added to it”. Experiments has been conducted to allow the students to understand the principle, but has always been the conventional method, measuring of the spring’s length. To actually determine the constant or other specifications of the spring, numerous experiments and multiple repetitions are needed. But with using manual measurement, there might be varying data and also human errors. So by the use of a simple potentiometer, a simple force-length-voltage converter can be build.
System Overview:
The system overview block diagram is shown in figure 1.
Figure 1: System Overview Block Diagram of Force Sensing Device
With the spring as the main element of the device, it will be compressed by a certain amount of load. When the load compresses the spring, the potentiometer that is attached to the spring will move along as well with respect to the change in the length of the spring. To determine how much has the spring move, a basic voltage divider rule with the potentiometer is constructed. This voltage will be feed into DAQ 6008 using the analog inputs. The starting point and the ending point of the spring will be converted into voltage and are recorded. With this information, the relationship of the spring and the voltage can be formulated and place into LabVIEW 8.5 graphical programming file. Using the formula, any distance moved by the spring will be converted into voltage and decipher by LabVIEW 8.5. The instant value of the voltage as well as the amount of force acting on the spring is displayed on the front panel.
Results & Discussion:
The UI of force sensing device is relatively easy. Since there is no need much for a user input, it only includes 2 instant values, 2 progressive horizontal bars, a turn dial and an animation picture ring. The front panel of Force Sensing Device is shown in figure 2.
Figure 2: Front Panel of the Force Sensing Device
The voltage bar and the voltage numerical value show the input voltage value from the potentiometer. After formulating, the voltage will be converted into force value, which is shown by the force bar and the force numerical value. The force is inversely proportional with the input voltage. As for the graphic animation of the scale, an animation for a weight will be added to the scale after every 5N. With this, the user will be enable to know through graphic animation which range of force is on the Force Sensing Device. There are a total of 6 different ranges and 6 different coloured weights will be added to the scale. This Force Sensing Device has a maximum load of 30N.
This system can calculate the constant K of a spring. By adding loads to it, the input voltage value will increase and this data can be collected to perform calculations for the spring’s constant. Different springs can be used and comparison can be made to determine which spring is more efficient at different ranges of forces. This is cause by the spring’s constant as well as the length of the spring. For the current Force Sensing Device, it is most sensitive at the range of 10N to 30N. Due to the hardware limitation, the spring decompression back to its original length is not linear.
The programming block diagram is split into two sections, which are the formula conversion section and the animation picture ring section. The programming block diagram is shown below in figure 3.
Figure 3: Programming Block Diagram
To have the Force Sensing Device to support heavy weights, a sturdy and strong body structure have to be designed and build around the spring. The spring must also be incorporated with the potentiometer well so that the compression of the spring can be reflected perfectly by the change of resistance in the potentiometer. Figure 4 shows the working model of the Force Sensing Device.
Figure 4: Working Model of the Force Sensing Device
Conclusion
The Force Sensing Device using National Instrument LabVIEW 8.5 has successfully calculated the spring’s constant. With that constant, formula is form and conversion from voltage to force has been accurate up to plus/minus 1N. Errors have been minimized down to minimize down to a scale where it is negligible for that range of forces. A lot of time and manpower have been saved in forming a relationship between the force and the voltage level. Trouble shooting process of any data can be down quickly now with the data saved in Excel format which makes it easier to process.
For more information, contact:
Rodney Tan
Senior Lecturer
University College Sedaya International (UCSI), Malaysia
No:1, Jalan Menara Gading, UCSI Heights, 56000 Kuala Lumpur Malaysia
Tel: +6017-3078955
Fax: +603-91023606
Email: rodneyt@ucsi.edu.my
