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MKal32 Handbook

 

 

 

I. Contents 2

 

 

 

 

 

II. MKal32 - Arranging the Calibrator for the 32cm Helmet

The MKal32 is a mechanical device that positions the 5 sensors of the Articulograph AG100 in 72 different positions inside the measurement area. The signals of the 5 sensors are measured and registered on the 72 positions. The distance calculations of the measured signals can be improved by using this information.

 

A. Set-up and Functioning Principle

The mechanical device enables the calibrating magazine with the 5 sensors to be positioned on the measuring level. The support of the calibrator magazine is located on a movable disk, making it possible for the magazine to be positioned in three different radien.

 

1. Three Positions for the Calibrator Magazine

Diagram 1: The three possible positions of the calibrator magazine on the disk

 

The diagram shows the positions of the calibrator magazine in the co-ordination system. In the 0mm position sensor 3 is alligned in the centre of the disk. When the disk is turned, sensors 2 and 4 rotate in a circle with a radius of 10 mm. This is because the sensors in the magazine are arranged in distances of 10 mm. Correspondingly, sensors 1 and 5 create a circle with a radius of 20 mm.

 

In the 40 mm position, sensor 3 creates a circle with a radius of 40 mm. The radius of the circle created by sensors 2 and 4 is 40.99 mm and by sensors 1 and 5 is 44.45 mm.

In the 80 mm position, sensor 3 creates a circle with a radius of 80 mm. The radius of the circle created by sensors 2 and 4 is 80.62 mm and by sensors 1 and 5 is 82.46 mm.

 

 

2. Angle Positions of the Disk

 

 

The disk can be rotated and with the help of a lever on the back, can be arranged in 24 different positions. The arrangement in a notch corresponds to a turning of 15°.

Diagram 2: Three of the 24 possible angle positions of the disk

 

Diagram 2 shows how the positions of the sensors in the co-ordination system are changed by turning the disk. Three calibration magazines are drawn to show the possible positions. Only one calibration magazine is present when in use.

 

The co-ordination system is drawn in the way the measurement data is shown on the screen. In the MKal32 unit, the helmet is fastened in such a way that the neck coil is at the top. That means that the y-axle is to the left and the x-axle is on top (see diagram 3).

Diagram 3: The clock face serves as orientation for the angle positions

 

Diagram 3 shows the MKal32 unit in front of a clock face. The position of the hands represents the angle of the disk. In order to produce the correct distance, it is necessary that the magazine is fixed in the middle notch. In the "12 o'clock" position sensor 5 is located in the above left area and sensor 1 is in the above right area. Sensor 3 is located directly above the centre of the disk. The device is in the "12 o'clock" position when the lever points toward the top, to the neck coil.

The MKal unit and the calibrator unit in the helmet support each have one position in which the sensors are in the identical position in the measurement area. This is the"8 o'clock" position in the MKal32 unit on the radius 0. In the calibration unit (helmet support), it is the position when sensor 3 is in the centre and the magazine is not turned or tilted. In the helmet holder, the same ADC value will be shown when the calibrator magazine is not tilted and not turned.

 

 

B. Functioning Principle

The goal of the MKal program is to optimise the radius tables in the file "Ratab.art". These tables contain the distance (mm) to which each measured signal (ADC-value) of each sensor-transmitter coil corresponds.

Diagram 4: flow of data in a MKal calibration

 

The adjusted parameters for the Articulograph AG100 are found in the ART.cg file in the current directory (1). Through this, the MKal program can employ the valid parameters and operate the Articulograph AG100.

The new powers, determined in the course of the program (mean radius_K, radius_S and radius_N), can be saved in the Art.cfg file. These values are used when a calibration without the MKal, i.e. only with the Art program, is carried out.

With the MKal32 unit, the signal voltage of the 5 sensors on the 72 different positions can be measured (2). This information is used to determine the relationship between signal and distance for each sensor-transmitter coil combination. The results are 15 powers for the distance function. That means that for each channel (corresponding to the 5 sensors), a chin, neck and forehead exponent is determined that best describes the relationship between the sensor signal and the distance to the transmitter coil. The formula for the course of the signal voltage is:

where U is the measured signal voltage and R is the distance between sensor and transmitter coil.

The signals in the centre are measured with the sensor calibrator in the helmet holder (3). The sensor in the centre has an equal and known distance to each transmitter coil. With the adjustment handle, the sensor is turned and tilted in such a way that the maximal signal voltage is registered. By maximal signal voltage, the sensor is aligned parallel to the transmitter coil axis.

A table with 4096 distances is created for each sensor-transmitter coil with the measured data. These 4096 distances are the 4096 possible signal values that the Analogue-to-Digital-Converter can supply as sensor signals.

 

 

 

 

 

C. The Operating Program MKal

1. Installing and Running the Program

The following data files are part of the MKal program:

a) MKal.exe

b) BWCC.dll

c) Balken.dll

Copy the data in a new directory on your hard disk. To create the program symbol for the MKal program in the current window of the program manager, select in the following order:

Data New Program Search File MKal.exe

The symbol is then included in the Program-Manager and the MKal program can be started by clicking on the new program symbol and pressing the Return button.

After calling up the program, a menu bar, 6 function options, and a icon symbol for a configuration file appear in the window.

Diagram 5 The MKal Program

 

The symbol for the configuration file is "NoName.cfg" at the beginning. That means that the adjusted parameters for the Articulograph AG100 100 have not yet been loaded.

The function options contain all the functions that are necessary for the full MKal-calibration. The options are numbered in the sequence in which the calibration is run.

The other option present on the menu bar are helpful, but not necessary for running the program.

 

 

2. Necessary Steps for Calibration

a) Loading the Configuration of the Analogue Unit

The Articulograph AG100 must be set up correctly in order for the MKal program to function properly. The parameter for the adjustments are saved in the current directory of the "Art" program in the file "Art.cfg". This file must be loaded. At the end of the program, the updated parameters are saved in the "Art.cfg" file .

b) Recording measurements with the MKal Unit

The signals of up to 72 different positions in the measuring area can be measured and recorded. Because of the mechanical construction of the MKal32 Unit, the distances of the sensor and transmitters for each measured signal value are known.

All 72 positions must not be measured, but at least 10 positions must be measured.

c) Evaluating Calibration Data

The measured date is processed for further use. The corresponding distances are calculated and the statistical value is determined.

d) Determining the Power of the Distance Function

The exact distance that belongs to each signal value, for all 15 sensor-transmitter coil combinations are determined with the evaluated calibration data. The result is 15 exponents. The radius tables are calculated in the last stage of the program with this data.

e) Calibrating the Sensors

Next to distance, the rotation angle of the sensors to measuring surface is the most important influence on the signal strength. With the help of the calibration equipment of the helmet holder, each sensor is put into the centre of the measuring area and aligned parallel to the magnetic field. While you turn and tilt the sensor with the adjustment handle, the signal strength and its changes will be shown on the menu window. The maximum signal is created when the sensor is aligned parallel to the transmitter coil axis. Therefore, the largest measured signal is saved for further calculations.

These are the same actions as are done in the Service program Art.exe. The MKal program, however, enables better reporting. Fifteen separate exponents of the construction are used. The Art program takes into account only the mean value of the chin, forehead and neck coils.

f) Adjusting Radius Tables

The results of the complete MKal calibration are saved in the form of 15 tables in the file Ratab.art (in the current directory of the "ART" program). These tables show the distance of each sensor from the transmittor coils for each signal. This distance makes the calculation of the position possible.

3. Additional Functions in the Menu Lines

a) MKal - Opening Data

This function allows you to carry out an MKal calibration without having to use the position measurements with the MKal32 unit. To do this, load the measurement data that was saved from an earlier calibration. Be sure that previous measurement data is no longer valid when changing the adjusted parameters of the Articulograph AG100.

b) Saving Configurations Under....

You can prohibit the automatic transfer of the configuration file "Art.cfg" by using this menu function to save the current parameters in another file.

c) End

This is the end of the MKal program.

d) Using Help

This menu point calls up the "help" windows.

 

 

 

 

D. Carrying Out a MKal Calibration

1. Inserting the sensors in the calibrator magazine

The calibrator magazine has five notches over the lateral slits that are intended for the receiving of the sensors. This makes it possible for the exact positioning of the magazine in the calibration adjustment. As you can see in the diagram, the slits are thicker on one side of the magazine. To insert the sensors, the magazine should be held so that the notches are on top. The end of the magazine, in which the positioning slits lie, should point to the left. In this position four notches are located above four slits in the middle of the magazine. To the left there is one slit without a corresponding notch and to the right a notch without a slit under it.

Diagram 6: The calibrator magazine

The corresponding notches in the calibrator magazine are asymmetrical. When inserting the sensors, be sure that the lowest plated surface of the sensors lies on the flat side of the notch. Place the sensors beginning with channel one from right to left so that the cables run out of the left side of the magazine. Finally, the sensors should be reinforced with adhesive tape to guard against slippage.

 

2. Fastening the Helmet

Place the helmet on the MKal so that the red neck coil is on top (see diagram 3). The MKal32 unit is equipt with a clamp that enables you to fix the helmet to the base. The helmet can be clamped tight by lightly turning the screw with the hand. The blue coil will also be fixed to the base when this is done.

3. Inserting the Calibrator Magazine in the 0 mm Radius Position

You can see the MKal32 magazine in the position "12 o'clock" in the ART handbook on page 18. In this position sensor 5 is in the upper left position and sensor 1 is in the upper right position. Sensor 3 is located exactly above the centre of the disk. It is in the "12 o'clock" position when the adjustment lever points upward to the neck coil. The "8 o'clock" position on the radius 0 in the MKal32 corresponds to the position in the calibrator unit with sensor 3 in the centre.

After the MKal is brought into the "12 o'clock" position, the calibrator magazine should be inserted into the lowest of the three bore-holes so that it is lined up in the centre of the MKal disk. The insertion of the magazine is started with the forehead coil, i.e. from left to right, so that sensor 1 points toward the chin coil. The sensors should be on the upper-side of the magazine. Push the magazine far enough so that sensor 3 is in the centre of the disk.

In order to fix the magazine in this position, use the plastic rod that passes exactly in the slits of the magazine (see above). This bar should be positioned so that it catches in the third slit (the one under coil 4!). The magazine holder is equipt with two small bore-holes that allow the bar to be fastened with two rubber bands.

 

Caution: The mechanics of the MKal allow that other positions that the ones named here can be set up. However, the MKal program will only produce reliable values when the positioning is carried out in the manner described above.

 

 

4. Starting the MKal Program

The MKal program is started by double clicking on the MKal symbol in the data manager. A window with a menu list, 6 function options, and an icon symbol for a configuration file will appear. You can run a complete MKal calibration by clicking on the 6 function options one after another.

a) Loading Configurations

The file "open menu" will appear and you will have to select the current configuration file which is saved in the operating system parameters of the Articulograph AG100. For example, if the current operating program Art.exe is saved in the directory c\ema\Art, then must chose the data c:\ema\art\art.cfg.

Caution The current configuration file must be loaded!

b) Measuring Positions

 

 

 

 

 

When measuring positions, a dialogue window will appear with 24 points in a circle - corresponding to the angle position of the disk - and 3 points - corresponding to the radius in which the calibrator magazine is fitted.

(1) Recording Measurement Values in 24 Angle Positions

Diagram 7: The Dialogue Window for Measuring Positions

 

Beginning with the "12 o'clock" position, the 24 measurement values are shown on the screen. In the MKal program, the adjusted angle can be chosen by clicking on the appropriate position (1). By activating the option "measure" (2), the measurement of this position is saved and the MKal disk can be moved to the next position.

When turning the MKal disk, be sure that the position is adjusted as exactly as possible. In order to do this, the adjustment lever, located in the holder of the disk, can be engaged for the individual angle positions. To position the disk, lift the lever slightly and bring the disk into the desired position. Then press it against the holder until its peak engages exactly in the cone-shaped bore-hole that is intended for this purpose.

(2) Positioning the Calibrator Magazine for a 40 mm Radius

After the above mentioned 24 measurement values are recorded, the calibrator magazine has to be brought into a new position. To do this (in the "12 o'clock" position), it should be taken out of the bottom bore-hole of the MKal and placed in the middle one.

Placing the magazine in the new position should be done as described above.

(3) Recording Measurement Values in 24 Angle Positions

Afterward, bring the switch "radius " (3) to the "40 mm" position. The 24 measurement values will be determined anew.

(4) Positioning the Calibrator Magazine for an 80 mm Radius

Finally take the magazine (in the "12 o'clock" position) out of the middle bore-hole of the MKal and place it into the top one.

(5) Recording Measurement Values in 24 Angle Positions

Bring the switch "radius" (3) to the position "80 mm". The 24 measurement values will be determined anew. At this point, the 3 * 24 = 72 measurement values that serve as the basis for further evaluation have been recorded.

c) Processing MKal Data

The measured data is at this point processed for further evaluation. The corresponding distances are calculated and the statistical values are determined. An announcement widow reports the successful completion of the processing or, when necessary, lists the missing data needed for the running of the program.

d) Calculating Powers

The distance function, which assigns each signal value the most exact distance, is determined for all 15 sensor-transmitter combinations with the processed calibration data. The result is that 15 exponents are calculated with the help of the radius tables in the last step of the program. An announcement window reports the successful completion of the calculation or, when necessary, lists the missing data needed for its completion.

e) Calibrating the Sensors

The standard calibration of the sensors must be carried out at the end. To do this, place the helmet in the helmet holder again and the calibrator magazine in the calibrator mechanism with sensor 1 engaged in the centre.

After calling up the function, a dialogue window with three bars will appear.

Diagram 8: The dialogue window shows the signal voltage of the three transmitter coils.

 

The currently being measured signal voltage of a channel (1) and the largest measured signal voltage (2) are shown above. The bars (3) also show the change in the signal voltage. The changes are in relation to the beginning state. Here the bars are set at 50%. A new beginning state can be produced be clicking on the "again" option. This means that the bar will be so positioned that it shows the current signal voltage (1) at 50%. The maximum value (2) will continue to be set in the current values.

 

 

 

 

(1) Calibrating One Sensor

The 5 channels should be calibrated one after another. Only one signal at a time, the signal for the chosen channel, will be shown in the window (3). The calibrator magazine must be so engaged that the sensor that is to be calibrated is lined up in the middle of the measurement area.

(a) Selecting Channels

Five function options for the channels 1 to 5 are located in the bottom part of the dialogue window (3) Select the channel for which the sensor calibration should be carried out.

Caution: The sensor to be calibrated must be in the centre of the measurement area!

(b) Establishing the Beginning State

After you have positioned the sensor in the centre of the measurement area, you must establish the beginning state with the "again"(Nochmal) key. If necessary, you can repeatedly establish the beginning state.

(c) Maximum Adjustment

In the actual calibration process, turn and tilt the calibrator magazine in such a way that all three bars process the largest signal. If one of the bars reaches the right border, click on the "again" option to create the beginning state anew.

(d) Confirming the Measurements with "good"

As soon as you have aligned the sensors parallel to one another, you will see in the field "Max=" that saved values can no longer be exceeded by turning or tilting. These values show the signal voltage of the sensors in the centre by parallel alignment. Click on the option "good" (5) so that the program can save the signal values shown in the "Max=" field. With this, the calibration for this channel and sensor is secured.

(e) Positioning the Next Sensor in the Centre

Shift the calibrator magazine so that the following sensor is aligned in the middle position and repeat the above steps.

The channels you have already calibrated will be shown in the lower area of the dialogue window (6). In place of the word "channel", the word "good" is shown.

f) Calculating Radius Tables

All of the already produced results are evaluated so that for each channel, 3 tables are created. These 3 tables correspond to the 3 different distance calculations of each transmitter.

As soon as the calculations are carried out successfully, the "file open" menu will appear. Here you will be asked to give the file name and the directory for the radius table. Select the directory in which the Art.exe program is found (see "loading configurations). Select "Ratab.art"as file name so that the program Art.exe will use the newly constructed radius tables.

Caution: The operation program Art.exe uses only the file Ratab.art in the same directory.

g) Ending the Program

A double click on the system menu will end the MKal program. You can also select the option "end fill" in the menu bar.