Noah R. Van Zandt and James F. Myers

Cedarville University, Cedarville, Ohio

Richard B. Rogers

Glenn Research Center, Cleveland, Ohio

Motorized Beam Alignment of a Commercial X-ray 

Diffractometer

NASA/TM—2013-217853

April 2013
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Noah R. Van Zandt and James F. Myers

Cedarville University, Cedarville, Ohio

Richard B. Rogers

Glenn Research Center, Cleveland, Ohio

Motorized Beam Alignment of a Commercial X-ray 

Diffractometer

NASA/TM—2013-217853

April 2013

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135
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NASA/TM—2013-217853 1 

Motorized Beam Alignment of a Commercial X-ray Diffractometer 

Noah R. Van Zandt and James F. Myers 

Cedarville University 

Cedarville, Ohio 45314 

Richard B. Rogers 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Abstract 

X-ray diffraction (XRD) is a powerful analysis method that allows researchers to noninvasively probe 

the crystalline structure of a material. This includes the ability to determine the crystalline phases present, 

quantify surface residual stresses, and measure the distribution of crystallographic orientations. The 

Structures and Materials Division at the NASA Glenn Research Center (GRC) heavily uses the on-site 

XRD lab to characterize advanced metal alloys, ceramics, and polymers. 

One of the x-ray diffractometers in the XRD lab (Bruker D8 Discover) uses three different x-ray 

tubes (Cu, Cr, and Mn) for optimal performance over numerous material types and various experimental 

techniques. This requires that the tubes be switched out and aligned between experiments. This alignment 

maximizes the x-ray tube’s output through an iterative process involving four set screws. However, the 

output of the x-ray tube cannot be monitored during the adjustment process due to standard radiation 

safety engineering controls that prevent exposure to the x-ray beam when the diffractometer doors are 

open. Therefore, the adjustment process is a very tedious series of blind adjustments, each followed by 

measurement of the output beam using a PIN diode after the enclosure doors are shut. This process can 

take up to 4 hr to perform. 

This technical memorandum documents an in-house project to motorize this alignment process. Unlike 

a human, motors are not harmed by x-ray radiation of the energy range used in this instrument. Therefore, 

using motors to adjust the set screws will allow the researcher to monitor the x-ray tube’s output while 

making interactive adjustments from outside the diffractometer. The motorized alignment system consists of 

four motors, a motor controller, and a hand-held user interface module. Our goal was to reduce the 

alignment time to less than 30 min. The time available was the 10-week span of the Lewis' Educational and 

Research Collaborative Internship Project (LERCIP) summer internship program and the budget goal was 

$1200. In this report, we will describe our motorization design and discuss the results of its implementation. 

Overview 

The motorized alignment system consists of three major components: the gear motors, the main 

electronics unit, and the hand-held controller (Fig. 1). The gear motors are simply four brushed gear 

motors, one for each of the adjustment screws on the x-ray tube. The main electronics unit contains all of 

the major system electronics including the power supply, motor controller, and relays. Finally, the handheld controller contains the necessary switches and knobs to interface the user with the system. 

Additionally, the circuit schematic can be found in the Appendix. Table 1 shows motor nomenclature and 

adjustment functions. 

Full automation of the alignment process was also considered. However, the work needed to program 

a microcontroller and add emergency stops to prevent movement past physical limits would be a 

significant increase in complexity with marginal additional benefit if the goal of reducing alignment time 

to less than 30 min via remote manual control could be achieved.
NASA/TM—2013-217853 2

TABLE 1.—MOTORS

Motor Designation Adjustment

Upper adjust gear motor M1 Tube angle

Lower adjust gear motor M2 Tube height

Side adjust gear motor M3 Tube twist

Monochrometer gear motor M4 Monochrometer angle

Figure 1.—System block diagram.

Motors

We chose to use brushed dc motors because they are simpler and easier to control than other motor 

types. By also making the motors geared, we allowed the user to be able to fine tune much easier because 

of the motor’s lower speeds.

After making these choices, we roughly determined the amount of torque needed to turn each screw 

by using a torque wrench (Table 2). We only measured the monochrometer and side screw torques. These 

two measurements bounded the problem because the side screw clearly required the most torque and the 

monochrometer screw was much easier to turn than the other three.

With these measurements in mind, we chose motors that could easily handle the load. The ones that 

we selected are oversized by more than 110 percent (Table 3).
NASA/TM—2013-217853 3

TABLE 2.—TORQUE MEASUREMENTS

Screw Turning clockwise,

lb-in.

Turning counterclockwise,

lb-in.

Side 5.8 6.8

Monochrometer 3.0 2.4

TABLE 3.—GEAR MOTOR SPECIFICATIONS

Motor Rated speed,

rpm

Rated torque,

lb-in.

Rated current,

A

Monochrometer 24 6.5 0.097

Other three 28 17.4 5.0

Motor Mounts and Couplers

To attach our motors to the tube housing, we created custom mounts out of aluminum. We chose 

aluminum because it is lightweight and is much easier to machine than other materials. Each mount was 

attached to the tube housing using already available features, with the exception of tapping several 

existing holes. We decided to attach the motors loosely to their mounts so that the motors would be free 

to move. This reduced the radial forces from any slight misalignment that could otherwise damage the 

motor’s bearings.

We also fabricated couplers to connect the motor shaft with the Allen wrench heads needed to turn 

the screws. The couplers were made from aluminum and attached using set screws. Figure 2 shows the 

motors mounted on the diffractometer.

Motor Controller

We selected a simple bidirectional H-bridge motor controller (Fig. 3) because it properly balanced 

control precision, simplicity, reliability, and build time for this project. The H-bridge type controller is 

capable of fairly precise speed control in either the clockwise or counterclockwise direction. It is capable 

of throttling from 0 to 100 percent. However, this throttling does not produce 0 to 100 percent speed 

control of the motor due to the numerous non-ideal factors of a DC motor’s response. Namely, winding 

losses, magnetic core hysteresis, the difference between static and dynamic friction, and other factors 

limit the actual control of the motor’s speed to approximately 10 to 100 percent. Those numbers were 

estimated during testing of the actual motor controller, motors, and tube housing.

Still, we decided that this level of control should be sufficient considering the gear motors’ full speeds 

of about 30 rpm. This means that the user can throttle the motors down to 3 rpm, or one revolution every 

20 sec. If the user then precisely stops the motor with 0.2 sec precision, the position can be controlled to 

within 3.6°. Our testing showed that a human is capable of consistently recognizing a trigger condition 

and pressing a button or flipping a switch within 0.1 sec of that trigger. So we believe that 0.2 sec

precision is reasonable for most users. 

Additionally, the particular motor controller chosen used a very simple control scheme based upon 

four operational amplifiers. This solution is purely analog, making it easier to troubleshoot in the event 

that a component should malfunction. However, this chance should be very low due to the relatively 

minimal number of components used in the controller. We chose to purchase a fully assembled motor 

controller because we did not have time to design, select components, construct, test, and revise a new 

controller design from scratch.
NASA/TM—2013-217853 4

Figure 2.—Motors mounted on diffractometer.

Figure 3.—Bidirectional H-bridge motor controller.
NASA/TM—2013-217853 5

Main Electronics Box

The main electronics box houses the power supply, relays, motor controller, and other small 

electronics (Fig. 4). It is designed to sit inside the x-ray diffractometer’s cabinet. The box itself is made of 

thick ABS plastic and is oversized for possible future expansion. 

Fuse

Power enters the box through the 120 V AC receptacle. The line wire was then immediately run 

through a 2 A fast-blow fuse. This fuse protects the system from excessive currents. 

Power Supply

The power supply that we selected is a commercial quality unit rated for very long life (Fig. 5). It 

provides 5, 12, and –12 V. Additionally, the supply requires a minimum load, as shown in Table 4, which 

we supplied via three power resistors, one attached to each of the voltage outputs. We actually chose to 

supply half the manufacturer’s recommended minimum load, as our testing showed this condition was 

sufficiently stable for our system. 

Power Resistors

As stated previously, three power resistors were added to supply a minimum load to the power supply

(Fig. 6). They are attached to a piece of aluminum, which is located near the exhaust holes and serves as a

simple heat sink for cooling.

 

Figure 4.—Main electronics box. Figure 5.—The power supply in the main electronics box.

TABLE 4.—POWER SUPPLY MINIMUM LOADING

Supply 

voltage,

V

Recommended 

minimum load

Chosen load Resistor value,

ohms

5 2.0 A 1.0 A 5

12 500 mA 240 mA 50

–12 100 mA 60 mA 200
NASA/TM—2013-217853 6

 

Relays

The main electronics box contains 5 relays (Fig. 7). Four of them connect the motor controller’s 

output to one of the four motors, depending on the position of the 5 position switch on the hand-held 

controller. The other relay connects 12 V power to the motor controller when the power switch is flipped 

on the hand-held and the push-button is pressed. These relays are all standard automotive 30 A relays. 

They were selected both for durability and for ease of replacement. They are also greatly oversized 

considering that the maximum expected load to one of the large motors is 5 A.

All relays have flyback diodes connected between the relay coil contacts. These diodes prevent a 

large voltage build up and spark when the relay is turned off due to the stored magnetic field in the coil. 

This significantly increases the lifetime of the switches which control the relays by reducing sparking 

during an opening condition. 

Cooling

When we added power resistors to our design to provide minimum load to the power supply, we 

determined that the main electronics box would need a small cooling fan to eliminate any chance of 

overheating. We added a 60 mm fan that pulls air into the case and blows it over the major electronics. 

The air then exits through the back, flowing over the power resistors and carrying their heat out of the 

enclosure.

Serial and Motor Cables

The control cable connecting the main electronics box to the handheld controls is a 14- conductor, 

shielded, twisted-pair cable with a male serial connector on the end that connects to the main electronics 

box. The shielding consists of both foil and 90 percent coverage braid. It uses 28 gauge conductors which 

can handle 226 mA.

The motors are connected to the main electronics box through four custom cables. One end of each 

cable terminates in a two-position Molex connector, which mates with connectors on the main electronics 

box. The other end has quick connection terminals which slide onto the motor leads. The polarity of the 

connection with the motor leads is not critical, as flipping the connection will simply reverse the direction 

of rotation. We designed the system such that rotating the control knob on the hand-held clockwise will 

cause the selected motor to rotate clockwise, and vice versa.

Figure 6.—The power resistors in the main electronics 

box.

Figure 7.—The relays in the main electronics box.
NASA/TM—2013-217853 7

Figure 8.—Handheld controller.

Handheld Controller

The layout for our handheld controller is fairly simple (Fig. 8). We used a terminal block to allow easy 

access to certain voltage supplies and connections. We have an on/off switch, which controls power to the 

motor controller. When the switch is turned on, the red LED lights up. We also have a motor selection 

switch. The switch can be in one of the following five positions: None, M1, M2, M3, and M4. Positions M1 

through M4 each operate a single motor. In the “None” position, no motor will be activated. A potentiometer

controls the speed and direction of the motors. The farther the potentiometer is turned, the faster the selected 

motor will spin. However, the motor will only turn if the user presses the pushbutton. The pushbutton can be 

held in for large movements or pressed and released quickly for fine tuning.

Results

The alignment time goal was met. Motor installation, beam alignment, and motor removal were 

accomplished in less than half an hour. The design, commercial component procurement, mount fabrication, 

assembly, and testing were all performed by the authors within the span of the 10-week internship plus a

1-week extension for one of the authors to implement and test the momentary pushbutton feature of the 

handheld controller. The total cost of items procured for the project was under $900.

NASA/TM—2013-217853 9

Appendix—Circuit Schematic
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Motorized Beam Alignment of a Commercial X-ray Diffractometer 

5a. CONTRACT NUMBER

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6. AUTHOR(S)

Van Zandt, Noah, R.; Myers, James, F.; Rogers, Richard, B. 

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WBS 561581.02.08.03.47.01.02 

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National Aeronautics and Space Administration 

John H. Glenn Research Center at Lewis Field 

Cleveland, Ohio 44135-3191 

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9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

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13. SUPPLEMENTARY NOTES

14. ABSTRACT

X-ray diffraction (XRD) is a powerful analysis method that allows researchers to noninvasively probe the crystalline structure of a material. 

This includes the ability to determine the crystalline phases present, quantify surface residual stresses, and measure the distribution of 

crystallographic orientations. The Structures and Materials Division at the NASA Glenn Research Center (GRC) heavily uses the on-site 

XRD lab to characterize advanced metal alloys, ceramics, and polymers. One of the x-ray diffractometers in the XRD lab (Bruker D8 

Discover) uses three different x-ray tubes (Cu, Cr, and Mn) for optimal performance over numerous material types and various experimental 

techniques. This requires that the tubes be switched out and aligned between experiments. This alignment maximizes the x-ray tube’s output 

through an iterative process involving four set screws. However, the output of the x-ray tube cannot be monitored during the adjustment 

process due to standard radiation safety engineering controls that prevent exposure to the x-ray beam when the diffractometer doors are 

open. Therefore, the adjustment process is a very tedious series of blind adjustments, each followed by measurement of the output beam 

using a PIN diode after the enclosure doors are shut. This process can take up to 4 hr to perform. This technical memorandum documents an 

in-house project to motorize this alignment process. Unlike a human, motors are not harmed by x-ray radiation of the energy range used in 

this instrument. Therefore, using motors to adjust the set screws will allow the researcher to monitor the x-ray tube’s output while making 

interactive adjustments from outside the diffractometer. The motorized alignment system consists of four motors, a motor controller, and a 

hand-held user interface module. Our goal was to reduce the alignment time to less than 30 min. The time available was the 10-week span of 

the Lewis' Educational and Research Collaborative Internship Project (LERCIP) summer internship program and the budget goal was

$1200. In this report, we will describe our motorization design and discuss the results of its implementation.

15. SUBJECT TERMS

Controllers; Alignment; X-ray diffraction 

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