Description:
The program for this assignment comes from a research project I did while I worked at KUMED. A researcher was studying stroke patients and their ability to regulate the forces used to lift something. Here's the motivation:
"When we lift something, we use an internal model to estimate how heavy it will be and we pre-program our grip forces. Once we've lifted something once or twice, we are really accurate in the forces we use. This is important because if a person doesn't apply enough grip force the object will slip out of their hand. If we apply too much we could damage the object. The same is true of the lifting force. If we were to apply too little force, we wouldn't be able to lift the object. Too much and we might throw it over our shoulder! People who have suffered a stroke have impaired brain function. We want to find out whether their ability to program their forces is affected."
A novel grip device was designed (see Figure 1). The device has two sensors, one in each grip pad. As a person grips and attempts to lift the device, the forces they exert are recorded.
To help with this problem here are some things to note:
• Figure 2 shows typical forces for a lift trial. The grip force has an initial peak and then stabilizes. It is the stable region that we will use to determine if the force applied is accurate.
• The object mass is 265g. To find the weight in N use F = ma, where m is the mass of the object (kg) and a = gravity (9.81m/s2)
The file device_data.txt contains force data for multiple lift trials.
A program needs to be written to:
1) For each trial:
a. Liftoff time (s) - Determine the time the object was lifted from the table. To lift the object, a total lift force greater than or equal to the object weight (N) must be used. The data was sampled at 400 pts /second. Once you identify what point in the trial is the point of liftoff, the liftoff time (s) would be pt/400. For example, if the 200th pt is liftoff, then 200/400 = 0.5s
b. Stable grip force (N) - Calculate the grip force during the stable region. Use ginput to get the user to select the start and end of the stable region.
2) Calculate the average liftoff time over all trials.
3) Calculate the average stable grip force over all trials.
4) Determine whether the participant used accurate grip forces.
a. If the average stable grip force is within 5% of the weight (N) of the device, grip forces are considered accurate.
5) Display the average liftoff time and whether the participant used accurate grip forces.
Hints:
• Use load to get data from the file HW5_data.txt into a MATLAB variable. Each trial consists of two columns of data, lift force and grip force. The file contains 4 columns of data, where columns 1 and 2 contain the data for the first trial, columns 3 and 4 contain the data for the second trial. Using a variable to index the data file is a good way to make sure your program could handle a larger data set (data for trial i is in columns (i*2)-1 and i*2).
• A while loop would be a good choice for finding liftoff time, but make sure you handle the case that the participant doesn't lift the object at all (lift force never gets to object weight).
• Check the help for how to use ginput. You might use a command like this:
[(stable_start_x),y] = ginput(1);
• The results you get from ginput will need to be rounded to the nearest integer so you can use them to index your data (use the round function).