INCLINED PLANE RIG LABORATORY USER GUIDE VERSION 1.3

Transcription

1 INCLINED PLANE RIG LABORATORY USER GUIDE VERSION 1.3 Labshare 2011

2 Table of Contents 1 Introduction Remote Laboratories Inclined Plane - The Rig Apparatus Block Masses & Inclining the Ramp Release Stop & Air Pressure Cylinders Displacement Sensor Motor and Encoder Data Acquisition & Feedback Rig Session Using the Rig Page Data Acquisition Rig Control Software Experiment Data File Transfer FAQ & Troubleshooting References /08/2010 First draft LaReine Yeoh /08/2010 Revision LaReine Yeoh /09/2010 Internal Release Ellie Burke /12/2010 Revision and general formatting Ellie Burke /03/2011 Screenshot update Ellie Burke /06/2011 Labshare Logo added Ellie Burke Labshare 2011 Page 2

3 1 Introduction 1.1 Remote Laboratories Remote laboratories enable students to access physical laboratory apparatus through the internet, providing a supplement to their studies and existing hands-on experience. Students carry out experiments using real equipment, but with much greater flexibility since access can occur from anywhere and at any time. Their interaction with the remote equipment is assisted by the use of data acquisition instrumentation and cameras, providing direct feedback to students for better engagement. Traditional engineering laboratories require students to be physically present in order to work with equipment, which may limit student flexibility. Conversely, remote laboratories let students work in their own time and even repeat experiments for better learning outcomes. Of course students cannot actually touch and feel the equipment in a remote laboratory, but they can still perform most other tasks relevant to their learning. Sometimes, separation from potentially hazardous equipment is preferable from a safety point of view. Due to the increased use of remote operation in industry, where machinery and entire plants are often controlled from a distant location, students may directly benefit from learning how to remotely control equipment. Furthermore, remote laboratories provide the opportunity to access a wider range of experiments as costly or highly specialised equipment may not be locally available. This presents the opportunity to share laboratory facilities between institutions. Significant research and pilot studies have been undertaken in Australia and by several groups around the world into the educational effectiveness of using remote laboratories. These studies have consistently shown that, if used appropriately in a way that is cognizant of the intended educational outcomes of the laboratory experience, remote laboratories can provide significant benefits. Indeed, multiple research studies have demonstrated that whilst there are some learning outcomes that are achieved more effectively through hands-on experimentation (e.g. identification of assumptions, specific haptic skills), there are other learning outcomes that are achieved more effectively through remotely accessed laboratories (e.g. processing of data, understanding of concepts). 1.2 Inclined Plane - The Rig Apparatus The Inclined Plane Rig was constructed to study the physics of frictional forces on a given mass with different materials as they slide down an aluminium ramp. The rig hosts 3 blocks of similar mass, with each block having a different material in contact with the incline ramp itself. The Incline Plane Rig comprises of the following main components: 3 block masses, each with a different material Block 1 Nylon Block 2 Aluminium Block 3 Acrylic A single displacement sensor running along the length of the ramp Cylinders which lock the blocks into position at either end of the ramp A release stop so that all 3 blocks start from the same position each time A motor and an encoder to drive and monitor the angle of the ramp Limit switches beyond which the ramp will not incline Data acquisition and control hardware Web camera for visual feedback (integrated into the Control Software) Control software front end written in LabVIEW Labshare 2011 Page 3

4 Store Zone Pistons Displacement Sensor Gate Piston Drop Zone Pistons Guide Rail Block Masses Electric Motor & Gear Set Emergency Stop Button Figure 1: Inclined Plane Rig in its default state with zero degrees incline Block Masses & Inclining the Ramp There are 3 blocks of similar mass each 60 x 40 x 40 mm in dimension, and having a different material which comes into contact with the surface of the ramp, Block 1 (267.6g) Nylon Block 2 (275.5g) Aluminium Block 3 (278.3g) Acrylic The blocks are initially stored in the Drop Zone on the right-hand side of the ramp as shown in Figure 1. When a block and an angle are selected for the experiment run, the rig will first automatically slide unwanted blocks away from the chosen block (by letting them slide towards Store Zone on the left-hand side of the rig, if located in front of the chosen block). Then, the selected block is moved into position against the Release Stop before the ramp is settling at the targeted angle. When the user selects to release this block and begin measurement, it too will slide towards the Store Zone on the left and its displacement along the ramp recorded. Each block has a magnet embedded in the middle at the back from which its location along the ramp can be tracked via the displacement sensor Release Stop & Air Pressure Cylinders There are 6 gas cylinders used to control block movement, which operate using air pressure supplied by an external compressor, and a series of valves. One cylinder holds a block in its starting position, while the remaining 5 have pins that are used to lock the blocks into place at either end of the ramp to prevent them from sliding unnecessarily as the ramp swings into action Displacement Sensor The amount of vibration displacement of each level is measured by a contactless C-series Magnetostrictive Linear-Position Sensor. Button magnets are fixed at the back of each block, which travel along the Labshare 2011 Page 4

5 waveguide sensing element inside the sensor as the block moves along the ramp. The effect of this external magnetic field causes the ferromagnetic material of the waveguide to change its shape at that particular point on the sensor. To read the magnet's position, an interrogation current pulse is sent along the waveguide from the base of the sensor, which generates a radial magnetic field as it travels. When it reaches the point at which the button magnet is currently located, the two magnetic fields interact with one another, and a mechanical strain pulse is emitted back towards the base of the sensor (in the form of an impact sound-wave ) which is detected and converted into a voltage signal by the sensor electronics [1] Motor and Encoder A servo controller is used to send signals to the motor which drives the ramp to the right angle. A separate encoder is used to determine the exact angle of the ramp to within ±0.01 o. On startup, the Incline Plane Rig will run through an initialization routine, during which it determines its zero position where the ramp is completely horizontal, by seeking left and right of this position. Once found, this becomes the default state to which the rig will return after every experimental run is complete, shown in Figure 1. A set of limit switches are located along the Encoder shaft which protect the rig from rotating into the table. The first level of protection are two soft limits which are software activated, preventing the user from driving the rig too far clockwise or counter-clockwise. A pair of hard limits are also located at either end which immediately cut power to the rig if tripped, preventing further motion of the rig. If this happens during the course of the experiment, please contact the relative administrator as hardware reset will be necessary Data Acquisition & Feedback Data acquisition and control is implemented using a LabJack UE9 device and is linked to the Rig Server PC via an Ethernet connection. Software written in LabVIEW, is hosted on a remote machine running Windows XP allowing users the full luxury of a desktop environment from which operate. A USB webcam with a fisheye lens gives the user visual feedback of the Inclined Plane in action, in real-time which is integrated into the control software itself. Labshare 2011 Page 5

6 2 Rig Session The following section outlines the procedure for using the Inclined Plane Rig, which is similar to other Remote Laboratory Rig types used in the past. The software that runs the Remote Laboratories and provides access to the rigs through a web browser is called Sahara. For the purpose of using the rig, it is assumed that users have access to a workstation that meets the system requirements. Users should refer to Labshare s Generic Rig Access Guide for this information. After logging in with a username and password, the user will be directed to the Rig Selection page. Selecting the Inclined Plane rig under Rig Types will allocate the user to the rig. However, if the user wishes to access a particular rig, then this can be selected in the Specific Rigs section. Once a rig is selected, a popup window will appear, asking if the user wishes to join in the queue for the chosen rig. By clicking Queue button, the user will be granted access to the selected Incline Plane Rig. If the rig is In Use status, the user will be put in waiting list to access the rig until the current user and any other previously queued users are finished. The user s position in the queue may be forfeited if the user navigates away from the queue page. Labshare 2011 Page 6

7 2.1 Using the Rig Page If the rig is free, the user will immediately be taken to the rig page where the user can access the Inclined Plane rig control software. Each user has a designated session timeframe within which to conduct their experiments. A countdown timer at the top left of the page shows how much time the user has left on the rig. This may be automatically extended if no one else is waiting for the rig. The rig session starts as soon as the user is directed to the Rig Session page. If the user does not utilize the rig session within the timeline that is given, the rig session may be forfeited. By clicking on the green Launch button at the bottom of the screen, the LabVIEW control application will be automatically launched from its remote location. Note that it may take a couple of seconds for the user s remote connection to be established. Next screenshot indicates the user interface that is properly launched to use. Labshare 2011 Page 7

8 Once finished with the experiment, the user can exit by closing the control software window or press the red Terminate button under Rig Control at the left of the Inclined Plane Session page. This will allow the rig to shut itself down and close the control software properly. If the user has finished using the rig completely, back in the Inclined Plane page, the user can exit the session by pressing the Finish Session button. A popup window will appear asking for confirmation of exit. Selecting Yes will close the current remote connection to the rig and redirect the user to the Rig Selection page. It is important that the user exits the current rig session properly before logging out of the Remote Laboratories web page to allow other users to access the rig. Once successfully logged out, the user will be taken back to the main login page. 2.2 Data Acquisition Currently, there is only one method of transferring files generated or required to/from the Remote Labs server, which has a limited space. All data files on the Remote Labs server will be lost once the user exist the Rig Session page. Labshare 2011 Page 8

9 3 Rig Control Software This section describes how to use the Inclined Plane control software created in LabVIEW. Once the user s connection to the remote environment is established, the control software is automatically launched and will begin its initialization procedure. During this process, the status bar at the bottom right of the panel will indicate Initializing, please wait. The video feed from the Rig Session page shows what is happening to the rig in real-time, as it rotates in both directions to find its default starting position of 0 o. Once initialization is complete, the status bar at the bottom of the panel will turn green and state Ready and the rig will be at its initial, horizontal position. Labshare 2011 Page 9

10 To run an experiment, select any one of the 3 blocks from the bottom left of the screen, followed by entering an incline angle from the horizontal position under Set Angle. Note that the maximum angle possible is 42 0 ; any number above this will be coerced down to this maximum. Once the selection is made, the user can press the Run button. Labshare 2011 Page 10

11 The rig will then automatically move counter clockwise to the specified angle. If either blocks 2 or 3 are chosen, the rig will seek to the highest angle and release any block in front of the selected block first to get them out of the way by moving it to the Store Zone. The selected block will then be moved such that it rests against the manual release stop, at the specified angle. Once in position, the status bar will change to green and indicate that the Block is ready for release. To begin measurement, the user can press the Release button below the status bar. The manual release stop will then be lifted and the block will start to slide from right to left, down towards the store zone as seen in the video feed below. Whilst this is happening, the sensor is recording the position of the block every 0.01s and the graph (on the left) are updated in real time as the block slides. Labshare 2011 Page 11

12 The displacement dataset (white) shows the raw data from the sensor (after being boxcar filtered to reduce noise), whilst the velocity (red) and acceleration (green) curves are calculated over all displacement data collected in computer memory at that particular instance in time (for improved statistics) and plotted on the fly as the data is acquired. Once completed, the status bar will change to read Measurement complete. Resetting rig. In the live video feed, the rig will move back into its zero position whilst in the control software, the full displacement dataset (white) will be displayed on the graph. Note that the velocity (red) and acceleration (green) curves are calculated based on the raw data and plotted whilst the rig moves itself back into its default horizontal position. The steepness of the dataset and the speed at which the block falls is dependent on the angle chosen. If the angle for a particular material is too low, the block may not fall or may get stuck halfway, during which the measurement will time out, the status bar will turn orange and display this message. The rig will automatically move to reset itself and get the block out of the way. Labshare 2011 Page 12

13 Once back in its default position, the status bar is green and reads Ready. This indicates that the user is now able to do another experiment run by once again, selecting a block and an appropriate angle. Note that any block can be selected anytime as the status indicates Ready, including ones which are already in the Store Zone. The Inclined Plane Rig is capable of performing individual block resets. If the user wishes to repeat the same block run like previous one, all user needs to do is to press the run button again without changing the block and angle. The rig will automatically move the last block into position for manual release and get ready for another measurement. 3.1 Experiment Data File Transfer After a run is completed, the data displayed on the graph can be saved by clicking on the Save button in the bottom right hand corner of the LabVIEW control program. The data file is then automatically copied to a server from which it can be accessed via the Rig Session page under Session Files. Labshare 2011 Page 13

14 Any additional files after subsequent runs are stored here consecutively. To save a copy to the current local drive, the user can simply click on the file a popup window will then appear asking for the details of where the user wishes to save the file. For user convenience, all files are named with the following convention: <YYYMMDD>_<Timestamp>_<BlockType>_<angle>.txt Again, there is only one method of transferring files generated, so the user MUST save files before navigating away from the Rig Session page. Due to limited space on the Inclined Plane Rig remote server, all data files will be lost once the user exits the Rig Session page. Labshare 2011 Page 14

15 Once finished using the rig and saved all the data needed, the user can exit the Inclined Plane control software by clicking on the red Terminate button under Rig Control on the web page. The button will change to yellow as the rig initiates its shutdown procedure and close the control software properly. Labshare 2011 Page 15

16 4 FAQ & Troubleshooting Any questions regarding the nature of assessment tasks should initially be directed to the relevant academic. If the user encounters any difficulties using the rigs, the Contact Support button should be used to request assistance and report an incident. The following popup window will appear, allowing the user to enter the name and a valid address. Then the most appropriate category should be selected from the drop down list, and the purpose of the help request should be briefly stated. A more detailed description of the problem, comment or request can be given in the feedback textbox. Users are strongly encouraged to leave feedback and comments of their experience with the rigs to help improve the system, as well as any suggestions for additional features to be included in the future. For any enquires or assistance, contact the Labshare helpdesk at: helpdesk@labshare.edu.au Labshare 2011 Page 16

17 5 References [1] MTS Sensors (no date) Temposonics Linear-Position and Liquid-Level Sensors [accessed 6 th June 2011]. Labshare 2011 Page 17