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59-457: It defines a two-way communication protocol between the stylus and the computer and allows the stylus to remember user preferences for ink color and stroke. It support 9-axis inertial measurement . Products started coming to market in 2019 including one stylus and several Chromebooks from different manufacturers. By 2019, there were over 30 members, including Google and 3M, but some major players like Apple and Microsoft had not joined. As of 2022,

118-480: 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

177-416: 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

236-551: 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

295-508: 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

354-514: A number of rotary speed sensors that may be found in various parts of the vehicle. Speed sensor failures are frequent, and are mainly due to the extremely harsh operating conditions encountered in rail vehicles. The relevant standards specify detailed test criteria, but in practical operation the conditions encountered are often even more extreme (such as shock / vibration and especially electromagnetic compatibility (EMC)). Although rail vehicles occasionally do use drives without sensors, most need

413-448: 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

472-457: A rotary speed sensor for their regulator system. The most common type is a two-channel sensor that scans a toothed wheel on the motor shaft or gearbox which may be dedicated to this purpose or may be already present in the drive system. Modern Hall effect sensors of this type make use of the principle of magnetic field modulation and are suitable for ferromagnetic target wheels with a module between m =1 and m = 3.5 (D.P.=25 to D.P.=7). The form of

531-446: A shaft stub attached to the wheelset and fitted with a torque converter connected to the bogie frame to prevent it from rotating. The extreme vibration in this location leads to a considerable load on the pulse generator bearing, which, with this method of installation has to carry not only the relatively small mass of the pulse generator shaft but that of the entire pulse generator. When we consider that bearing life reduces with at least

590-412: A side effect on size and mass. A wireless IMU is known as a WIMU. Wheel speed sensor A wheel speed sensor ( WSS ) or vehicle speed sensor ( VSS ) is a type of tachometer . It is a sender device used for reading the speed of a vehicle's wheel rotation . It usually consists of a toothed ring and pickup. The wheel speed sensor was initially used to replace the mechanical linkage from

649-419: A slotted disk. Experience shows that the possible number of channels achievable by this technique is still not enough. A number of subsystems therefore have to make do with looped-through signals from the wheel slide protection electronics and are therefore forced to accept, for instance, the available number of pulses, although a separate speed signal might well have some advantages. The use of optical sensors

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708-497: A special problem: the circulating air that keeps the motors cool carries swarf abraded from the wheels and rails. This collects on the heads of magnetic sensors. There are also increasingly motors in which sensors have to scan aluminium target wheels, for instance because the impellers are made of an aluminium alloy and the manufacturer does not wish to have to shrink on a separate ferromagnetic gear rim. For these applications there are speed sensors available that do not require

767-453: A target magnet. A number of transmitting and receiving coils are used to generate an alternating electric field with a frequency of the order of 1 MHz and the modulation of the coupling between senders and receivers is then evaluated. This sensor is installation and signal compatible to the magnetic sensors; for most common target wheel modules the units can simply be replaced without any other measures being necessary. Customers often want

826-492: A wider range of air gap. The primary signal from a Hall sensor loses amplitude sharply as the air gap increases. For Hall sensor manufacturers this means that they need to provide maximum possible compensation for the Hall signal's physically induced offset drift. The conventional way of doing this is to measure the temperature at the sensor and use this information to compensate the offset, but this fails for two reasons: firstly because

885-462: Is a passive sensor with signal conditioning circuitry built into the device. This signal conditioning may be amplifying the signal's magnitude; changing the signal's form to PWM , square wave, or others; or encoding the value into a communication protocol before transmission. The vehicle speed sensor (VSS) may be, but is not always, a true wheel speed sensor. For example, in the Ford AOD transmission,

944-582: Is an electronic device that measures and reports 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

1003-456: 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

1062-403: 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

1121-534: 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

1180-504: Is increased over Hall sensors in fluctuating gap applications. Also the signal quality is much higher, enabling [interpolation] within the sensor/encoder or by an external circuit. There is a limit on the number of pulses achievable by Hall sensors without integrated bearings: with a 300 mm diameter target wheel it is normally not possible to get beyond 300 pulses per revolution. But many locomotives and electric multiple units (EMUs) need higher numbers of pulses for proper operation of

1239-469: Is narrowing rapidly. Magnetic Hall and magnetoresistive sensor systems can be imbedded in plastic or potting material, which increases mechanical reliability and eliminates damage from water and grease. Wheel speed sensors can also include hysteresis . This suppresses any extraneous pulses while the vehicle is at a standstill. Pulse generators constructed in accordance with this principle have been successfully field tested by several rail operators since

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1298-433: 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

1357-425: Is used to generate rectangular pulses from the sine/cosine signal periods. The precision encoder also possesses amplitude and offset correction functions. This makes it possible to further improve the signal quality, which greatly improves traction regulation. Bearingless speed sensors may be found in almost every wheelset of a rail vehicle. They are principally used for wheel slide protection and usually supplied by

1416-433: Is wider than that for conventional speed sensors on module m = 2 target wheels. On a module m = 2 target wheel the new speed sensors can tolerate gap of as much as 2.2 mm. It has also been possible to markedly increase the signal quality. Both the duty cycle and the phase displacement between the two channels is at least three times as stable in the face of fluctuating air gap and temperature drift. In addition, in spite of

1475-404: Is widespread in industry. They have two fundamental problems in functioning reliably for years, the optical components are extremely susceptible to dirt, and the light source ages too quickly. Traces of dirt greatly reduce the amount of light that passes through the lens and can cause signal dropout. These encoders are therefore required to be very well sealed. Further problems are encountered when

1534-455: 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

1593-594: The LED, but unfortunately this further accelerates the aging process. The principle used in scanning a ferromagnetic measuring scale magnetically does not exhibit these deficiencies. During many years’ experience of using magnetic encoders there have been occasions when a seal has failed and a pulse generator has been found to be completely covered in a thick layer of brake dust and other dirt, but such pulse generators still functioned perfectly. Historically, magnetic sensor systems cost more than optical systems, but this difference

1652-506: The VSS is mounted to the tailshaft extension housing and is a self-contained tone ring and sensor. Though this does not give wheel speed (as each wheel in an axle with a differential is able to turn at differing speeds, and neither is solely dependent on the driveshaft for its final speed), under typical driving conditions this is close enough to provide the speedometer signal, and was used for the rear wheel ABS systems on 1987 and newer Ford F-Series ,

1711-508: 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

1770-623: 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

1829-414: The bearing shells or covers of wheelsets offer a solution. Using a number of bearingless speed sensors would also involve additional cables, which should preferably be avoided for outdoor equipment because they are so susceptible to damage, for instance from flying track ballast . From one to four channels can be implemented, each channel having a photosensor that scans one of at most two signal tracks on

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1888-464: The beginning of 2005. The type test specified in EN 50155 has also been successfully completed, so that these pulse generators can now be delivered. Inside-journal bogies make particular demands on the pulse generator designer because they have no bearing cover on the end to serve as the basis from which the rotation of the wheelset shaft could be registered. In this case the pulse generator has to be mounted on

1947-546: 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

2006-439: The case of unitized bearing assemblies). The number of teeth is chosen as a trade-off between low-speed sensing/accuracy and high-speed sensing/cost. Greater numbers of teeth will require more machining operations and (in the case of passive sensors) produce a higher frequency output signal which may not be as easily interpreted at the receiving end, but give a better resolution and higher signal update rate. In more advanced systems,

2065-559: The complex electronics it has also been possible to increase the mean time between failures for the new speed sensors by a factor of three to four. So they not only provide more precise signals, their signal availability is also significantly better. An alternative to Hall effect sensors with gears are sensors or encoders which use [magnetoresistance]. Because the target wheel is an active, multipole magnet, air gaps can be even larger, up to 4.0 mm. Because magnetoresistive sensors are angle-sensitive and amplitude-insensitive, signal quality

2124-419: The construction more compact. In this case the maximum possible air gap is only 0.5 to 0.8 mm. For the design engineer, the visible air gap that the sensor ends up with is primarily the result of the specific machine design, but is subject to whatever constraints are needed to register the rotary speed. If this means that the possible air gap has to lie within a very small range, then this will also restrict

2183-446: The drift does not vary linearly with the temperature, and secondly because not even the sign of the drift is the same for all sensors. Some sensors now offer an integrated signal processor that attempts to correct the offset and amplitude of the Hall sensor signals. This correction enables a larger maximum permissible air gap at the speed sensor. On a module m = 1 target wheel these new sensors can tolerate an air gap of 1.4 mm, which

2242-482: The first pickups with ABS. Wheel speed sensors are a critical component of anti-lock braking systems . Many of the subsystems in a rail vehicle, such as a locomotive or multiple unit , depend on a reliable and precise rotary speed signal, in some cases as a measure of the speed or changes in the speed. This applies in particular to traction control , but also to wheel slide protection , registration, train control, door control and so on. These tasks are performed by

2301-432: 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

2360-433: The magnet is modulated by the passing target teeth. This modulation is registered by the Hall sensors, converted by a comparator stage to a square wave signal and amplified in a driver stage. The Hall effect varies greatly with temperature. The sensors’ sensitivity and also the signal offset therefore depend not only on the air gap but also on the temperature. This also very much reduces the maximum permissible air gap between

2419-426: The manufacturer of the wheel slide protection system. These sensors require a sufficiently small air gap and need to be particularly reliable. One special feature of rotary speed sensors that are used for wheel slide protection is their integrated monitoring functions. Two-wire sensors with a current output of 7 mA/14 mA are used to detect broken cables. Other designs provide for an output voltage of around 7 V as soon as

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2478-484: The measuring scale, right down to module m = 0.22. Likewise, the magnetoresistive sensors offer even higher resolution and accuracy than Hall sensors when implemented in motor encoders with integrated bearings. For even greater signal accuracy a precision encoder can be used. The functional principles of the two encoders are similar: a multichannel magneto-resistive sensor scans a target wheel with 256 teeth, generating sine and cosine signals. Arctangent interpolation

2537-432: The mechanical tolerances of the motor housing and target wheels to prevent signal dropouts during operation. This means that in practice there may be problems, particularly with smaller pitched target wheels of module m = 1 and disadvantageous combinations of tolerances and extreme temperatures. From the point of view of the motor manufacturer, and even more so the operator, it is therefore better to look for speed sensors with

2596-462: 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

2655-540: 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

2714-590: 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

2773-511: The promoters include Google, Intel, Lenovo, Samsung, and Synaptics. Dell, Sharp, and Wacom are contributors. While USI promotes itself as an open standard , access to detailed specifications is restricted to paying members. USI was launched on April 23, 2015, by a group of prominent OEMs, stylus and touch controller manufacturers. This computer hardware article is a stub . You can help Misplaced Pages by expanding it . Inertial measurement unit An inertial measurement unit ( IMU )

2832-407: The pulse generators are used in environments in which the dew point is passed: the lenses fog and the signal is frequently interrupted. The light sources used are light-emitting diodes (LEDs). But LEDs are always subject to aging, which over a few years leads to a noticeably reduced beam. Attempts are made to compensate for this by using special regulators that gradually increase the current through

2891-410: The sensor and the target wheel. At room temperature an air gap of 2 to 3 mm can be tolerated without difficulty for a typical target wheel of module m = 2, but in the required temperature range of from −40 °C to 120 °C the maximum gap for effective signal registration drops to 1.3 mm. Smaller pitch target wheels with module m = 1 are often used to get a higher time resolution or to make

2950-420: The signal frequency drops below 1 Hz. Another method used is to detect a 50 MHz output signal from the sensor when the power supply is periodically modulated at 50 MHz. It is also common for two-channel sensors to have electrically isolated channels. Occasionally it is necessary to take off the wheel slide protection signal at the traction motor , and the output frequency is then often too high for

3009-556: 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

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3068-401: The teeth can be asymmetrically shaped to allow the sensor to distinguish between forward and reverse rotation of the wheel. A passive sensor typically consists of a ferromagnetic rod which is oriented to project radially from the tone wheel with a permanent magnet at the opposite end. The rod is wound with fine wire which experiences an induced alternating voltage as the tone wheel rotates, as

3127-481: The teeth interfere with the magnetic field. Passive sensors output a sinusoidal signal which grows in magnitude and frequency with wheel speed. A variation of the passive sensor does not have a magnet backing it, but rather a tone wheel which consists of alternating magnetic poles produce the alternating voltage. The output of this sensor tends to resemble a square wave , rather than a sinusoid, but still increases in magnitude as wheels speed increases. An active sensor

3186-436: The teeth is of secondary importance; target wheels with involute or rectangular toothing can be scanned. Depending on the diameter and teeth of the wheel it is possible to get between 60 and 300 pulses per revolution, which is sufficient for drives of lower and medium traction performance. This type of sensor normally consists of two hall effect sensors , a rare-earth magnet and appropriate evaluation electronics. The field of

3245-430: The third power of the load we can see that a reliable and durable pulse generator for such a situation cannot merely be adapted from the more common standard pulse generator for outside-journal bogies merely by fitting and intermediate flange or similar construction. It really is necessary to have a pulse generator with a modified design adapted to the requirements of such a location. Some transport companies are faced with

3304-404: The traction converter, for instance when there are tight constraints on the traction regulator at low speeds. Such Hall effect sensor applications may benefit from built-in bearings, which can tolerate an air gap many orders of magnitude smaller because of the greatly reduced play on the actual sensor as opposed to that of the motor bearing. This makes it possible to choose a much smaller pitch for

3363-468: The wheel slide protection electronics. For this application a speed sensor with an integrated frequency divider or encoder can be utilized. A rail vehicle, particularly a locomotive , possesses numerous subsystems that require separate, electrically isolated speed signals. There usually are neither enough mounting places nor is there sufficient space where separate pulse generators could be installed. Multi-channel pulse generators that are flange-mounted onto

3422-470: The wheels to the speedometer , eliminating cable breakage and simplifying the gauge construction by eliminating moving parts. These sensors also produce data that allows automated driving aids like ABS to function. The most common wheel speed sensor system consists of a ferromagnetic toothed reluctor ring ( tone wheel ) and a sensor (which can be passive or active). The tone wheel is typically made of steel and may be an open-air design, or sealed (as in

3481-422: 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

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