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37-457: Its principal function on these rockets was to make navigation calculations using data from inertial sensor systems . It also performed readiness checks before launch. It was a digital serial processor using fixed-point data with 27-bit words. The storage was a drum memory . Electronic circuits were soldered encapsulated modules, consisting of discrete resistors , transistors , capacitors , and other components soldered together and encapsulated in

74-480: A magnetometer which is commonly used as a heading reference. Some IMUs, like Adafruit's 9-DOF IMU, include additional sensors like temperature. Typical configurations contain one accelerometer, gyro, and magnetometer per axis for each of the three principal axes: pitch, roll and yaw . IMUs are often incorporated into Inertial Navigation Systems , which utilize the raw IMU measurements to calculate attitude, angular rates, linear velocity, and position relative to

111-532: A body's specific force , angular rate, and sometimes the orientation of the body, using a combination of accelerometers , gyroscopes , and sometimes magnetometers . When the magnetometer is included, IMUs are referred to as IMMUs. IMUs are typically used to maneuver modern vehicles including motorcycles, missiles, aircraft (an attitude and heading reference system ), including uncrewed aerial vehicles (UAVs), among many others, and spacecraft , including satellites and landers . Recent developments allow for

148-494: A cam device located in the Servo Loop Amplifier Box. The sequence of events was controlled by a program device that was also used on Jupiter missiles. This was a 6-track tape recorder that sent pulses to a set of relays (the flight sequencer) to activate and deactivate various circuits in a precisely timed sequence. The ASC-15 was first flown on SA-5, the first Saturn I Block II vehicle and the first to achieve orbit. It

185-416: A certain direction vector were to measure a plane's acceleration as 5 m/s for 1 second, then after that 1 second the guidance computer would deduce that the plane must be traveling at 5 m/s and must be 2.5 m from its initial position (assuming v 0 =0 and known starting position coordinates x 0 , y 0 , z 0 ). If combined with a mechanical paper map or a digital map archive (systems whose output

222-551: A competing technology for use in motion capture technology. An IMU is at the heart of the balancing technology used in the Segway Personal Transporter . In a navigation system, the data reported by the IMU is fed into a processor which calculates altitude, velocity and position. A typical implementation referred to as a Strap Down Inertial System integrates angular rate from the gyroscope to calculate angular position. This

259-631: A foam material. It was manufactured in the IBM plant at Owego , NY. The first inertial guidance system for the Titan II was built by AC Spark Plug , and included an inertial measurement unit based on designs from Draper Labs at MIT , and the ASC-15 computer designed and built by IBM in Owego, NY. The first Titan II missile carrying this system was launched 16 March 1962. Acquiring spares for this system became difficult, and

296-508: A global reference frame. The IMU equipped INS forms the backbone for the navigation and control of many commercial and military vehicles, such as crewed aircraft, missiles, ships, submarines, and satellites. IMUs are also essential components in the guidance and control of uncrewed systems such as UAVs , UGVs , and UUVs . Simpler versions of INSs termed Attitude and Heading Reference Systems utilize IMUs to calculate vehicle attitude with heading relative to magnetic north. The data collected from

333-532: A motor on top of the drum housing, to avoid scoring the magnetic surface. See Figure 3. The Titan III was a space launch vehicle based on the Titan II ICBM. The ASC-15 was kept as the vehicle guidance computer, but the drum was lengthened slightly to provide 78 usable tracks, an increase of 20 over the drum used in the Titan II. The memory held 9,792 instructions (51 tracks) and 1,152 constants (18 tracks). The speed

370-448: A quadratic error growth in position. A constant error in attitude rate (gyro) results in a quadratic error growth in velocity and a cubic error growth in position. A very wide variety of IMUs exists, depending on application types, with performance ranging: To get a rough idea, this means that, for a single, uncorrected accelerometer, the cheapest (at 100 mg) loses its ability to give 50-meter accuracy after around 10 seconds, while

407-422: A side effect on size and mass. A wireless IMU is known as a WIMU. Specific force Specific force ( SF ) is a mass-specific quantity defined as the quotient of force per unit mass . It is a physical quantity of kind acceleration , with dimension of length per time squared and units of metre per second squared (m·s ). It is normally applied to forces other than gravity , to emulate

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444-410: A track was 1,728 bits. Instruction words were 9-bits long, and data was stored in 27-bit words. Coincident with 58 tracks were 67 read heads and 13 write heads. While the drum was spinning at 6,000 rpm, the heads floated above the surface of the drum on a thin layer of air. When the drum was spinning up or slowing down, the heads were raised off the drum by camshafts rotated by a chain that was driven by

481-456: Is based on both sensors and IMU models. Complexity for these models will then be chosen according to the needed performance and the type of application considered. Ability to define this model is part of sensors and IMU manufacturers know-how. Sensors and IMU models are computed in factories through a dedicated calibration sequence using multi-axis turntables and climatic chambers. They can either be computed for each individual product or generic for

518-468: Is because accelerometers measure the proper acceleration produced by the g-force exerted by the ground (gravity acting alone never produces g-force or specific force). Accelerometers measure specific force (proper acceleration), which is the acceleration relative to free-fall, not the "standard" acceleration that is relative to a coordinate system. In open channel hydraulics , specific force ( F s {\displaystyle F_{s}} ) has

555-403: Is fused with the gravity vector measured by the accelerometers in a Kalman filter to estimate attitude. The attitude estimate is used to transform acceleration measurements into an inertial reference frame (hence the term inertial navigation) where they are integrated once to get linear velocity, and twice to get linear position. For example, if an IMU installed in an aeroplane moving along

592-534: Is generally known as a moving map display since the guidance system position output is often taken as the reference point, resulting in a moving map), the guidance system could use this method to show a pilot where the plane is located geographically in a certain moment, as with a GPS navigation system, but without the need to communicate with or receive communication from any outside components, such as satellites or land radio transponders, though external sources are still used in order to correct drift errors, and since

629-433: Is necessary to compensate for three main resulting behaviors: Decreasing these errors tends to push IMU designers to increase processing frequencies, which becomes easier using recent digital technologies. However, developing algorithms able to cancel these errors requires deep inertial knowledge and strong intimacy with sensors/IMU design. On the other hand, if suspension is likely to enable IMU performance increase, it has

666-414: Is not a coordinate acceleration , but rather a proper acceleration , which is the acceleration relative to free-fall. Forces, specific forces, and proper accelerations are the same in all reference frames, but coordinate accelerations are frame-dependent. For free bodies, the specific force is the cause of, and a measure of, the body's proper acceleration. The acceleration of an object free falling towards

703-926: The Air Force decided to replace it with a new system. The AC Spark Plug system, including the ASC-15, was replaced by the Delco Electronics Universal Space Guidance System (USGS) on operational Titan II missiles starting in January 1978. The guidance computer in the USGS was the Magic 352 , made by Delco. The ASC-15 was built on an aluminum frame about 1.5 ft × 1.5 ft × 1 ft (46 cm × 46 cm × 30 cm). The sides, top and bottom were covered by pieces of laminated plastic, covered with gold-plated aluminum foil. These covers were slightly convex and ribbed for stiffness. Inside

740-455: The IMU's sensors allows a computer to track craft's position, using a method known as dead reckoning . This data is usually presented in Euler vectors representing the angles of rotation in the three primary axis or a quaternion . In land vehicles, an IMU can be integrated into GPS based automotive navigation systems or vehicle tracking systems , giving the system a dead reckoning capability and

777-677: The ST-90S and ST-124 systems (including the ASC-15 guidance computer) on SA-6 is shown in Figure 6. This is version 1 of the Instrument Unit, which flew on SA-5, 6, and 7. On SA-7 the ST-124 system guided the firing of both stages. The guidance and control system for SA-7 is shown in Figure 7. The digital computer is the ASC-15. It replaced both the cam device that contained the S-I tilt program for earlier missions and

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814-508: The ability to determine developmental levels of individuals when in motion by identifying specificity and sensitivity of specific parameters associated with running. Some gaming systems such as the remote controls for the Nintendo Wii use IMUs to measure motion. Low-cost IMUs have enabled the proliferation of the consumer drone industry. They are also frequently used for sports technology (technique training), and animation applications. They are

851-623: The ability to gather as much accurate data as possible about the vehicle's current speed, turn rate, heading, inclination and acceleration, in combination with the vehicle's wheel speed sensor output and, if available, reverse gear signal, for purposes such as better traffic collision analysis. Besides navigational purposes, IMUs serve as orientation sensors in many consumer products. Almost all smartphones and tablets contain IMUs as orientation sensors. Fitness trackers and other wearables may also include IMUs to measure motion, such as running. IMUs also have

888-546: The best accelerometer (at 10 μg) loses its 50-meter accuracy after around 17 minutes. The accuracy of the inertial sensors inside a modern inertial measurement unit (IMU) has a more complex impact on the performance of an inertial navigation system (INS). Gyroscope and accelerometer sensor behavior is often represented by a model based on the following errors, assuming they have the proper measurement range and bandwidth: All these errors depend on various physical phenomena specific to each sensor technology. Depending on

925-494: The covers were fifty-two logic sticks, each containing four welded encapsulated modules. These surrounded a bell frame housing a drum memory. See Figure 2. The drum was a thin-walled stainless steel cylinder 3 in (76 mm) long and 4.5 in (110 mm) in diameter covered with a magnetic nickel-cobalt alloy. It was driven by a synchronous motor at 6,000 rpm. The drum had 70 tracks, of which 58 were used and 12 were spare. These tracks were used as follows: The capacity of

962-534: The earth depends on the reference frame (it disappears in the free-fall frame, also called the inertial frame), but any g-force "acceleration" will be present in all frames. This specific force is zero for freely-falling objects, since gravity acting alone does not produce g-forces or specific forces. Accelerometers on the surface of the Earth measure a constant 9.8 m/s^2 even when they are not accelerating (that is, when they do not undergo coordinate acceleration). This

999-432: The guidance system is continually integrating acceleration with respect to time to calculate velocity and position (see dead reckoning ) , any measurement errors, however small, are accumulated over time. This leads to 'drift': an ever-increasing difference between where the system thinks it is located and the actual location. Due to integration a constant error in acceleration results in a linear error growth in velocity and

1036-462: The pilot entered in the aircraft longitude and latitude at takeoff, the unit would show the pilot the longitude and latitude of the aircraft in relation to the ground. Positional tracking systems like GPS can be used to continually correct drift errors (an application of the Kalman filter ). A major disadvantage of using IMUs for navigation is that they typically suffer from accumulated error. Because

1073-540: The position update frequency allowed by inertial navigation systems can be higher than the vehicle motion on the map display can be perceived as smooth. This method of navigation is called dead reckoning . One of the earliest units was designed and built by Ford Instrument Company for the USAF to help aircraft navigate in flight without any input from outside the aircraft. Called the Ground-Position Indicator , once

1110-590: The production of IMU-enabled GPS devices. An IMU allows a GPS receiver to work when GPS-signals are unavailable, such as in tunnels, inside buildings, or when electronic interference is present. IMUs are used in VR headsets and smartphones , and also in motion tracked game controllers like the Wii Remote . An inertial measurement unit works by detecting linear acceleration using one or more accelerometers and rotational rate using one or more gyroscopes . Some also include

1147-445: The program device that controlled the sequence of events on those missions. The next mission flown after SA-7 was SA-9. It carried a new version of the Instrument Unit, one that was unpressurized and 2 feet (0.61 m) shorter than version 1. Version 2 flew on the remaining Saturn I missions (SA-8, 9, and 10). Inertial measurement unit An inertial measurement unit ( IMU ) is an electronic device that measures and reports

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1184-426: The relationship between gravitational acceleration and gravitational force . It can also be called mass-specific weight (weight per unit mass), as the weight of an object is equal to the magnitude of the gravity force acting on it. The g-force is an instance of specific force measured in units of the standard gravity ( g ) instead of m/s², i.e., in multiples of g (e.g., "3 g "). The (mass-)specific force

1221-556: The targeted applications and to be able to make the proper sensor choice, it is very important to consider the needs regarding stability, repeatability, and environment sensitivity (mainly thermal and mechanical environments), on both short and long terms. Targeted performance for applications is, most of the time, better than a sensor's absolute performance. However, sensor performance is repeatable over time, with more or less accuracy, and therefore can be assessed and compensated to enhance its performance. This real-time performance enhancement

1258-422: The whole production. Calibration will typically improve a sensor's raw performance by at least two decades. High performance IMUs, or IMUs designed to operate under harsh conditions, are very often suspended by shock absorbers. These shock absorbers are required to master three effects: Suspended IMUs can offer very high performance, even when submitted to harsh environments. However, to reach such performance, it

1295-534: Was a passenger on this mission, not guiding the vehicle but generating test data for later evaluation. The active guidance system on SA-5 was similar to that of earlier flights. The passenger system was the ASC-15 and the ST-124 inertial platform . Guidance was open loop; that is guidance commands were functions only of time. SA-5 also saw the introduction of the Instrument Unit . On SA-6, while open loop ST-90S guidance

1332-452: Was the same as for the Titan II: 100 revolutions/second × 64 words/revolution × 27 bits/word = 172.8 kilobits/second. The time for an addition operation was 156 μs ; for a multiplication, 1,875 μs ; and for a division, 7,968 μs . No guidance computer was used for Saturn I Block I (missions SA-1, 2, 3 and 4). The guidance system for SA-2 is shown in Figure 4. The pitch program was provided by

1369-401: Was used for the first stage (S-I), after separation the ST-124 and ASC-15 used path adaptive guidance (closed loop) to control the second stage (S-IV). The SA-6 guidance system is shown in Figure 5. The effectiveness of the path adaptive guidance was demonstrated inadvertently when premature shutdown of S-I engine number eight had virtually no effect on the vehicle trajectory. The arrangement of

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