ADXL371
Recommended for New Designs
The ADXL371 is an ultra low power, 3-axis, ±200 g microelectromechanical system (MEMS) accelerometer that consumes 28 µA at a 2560 Hz output data rate...
Datasheet
ADXL371 on Analog.com
ADXL372
Recommended for New Designs
The ADXL372 is an ultralow power, 3-axis, ±200 g MEMS accelerometer that consumes 22 µA at a 3200 Hz output data rate (ODR). The ADXL372 does not power...
Datasheet
ADXL372 on Analog.com
ADXL314
Recommended for New Designs
The ADXL314 is a ±200 g range, 13-bit resolution, 3-axis digital accelerometer. The digital output data is formatted as 16-bit, twos complement data and...
Datasheet
ADXL314 on Analog.com
ADXL375
Recommended for New Designs
The ADXL375 is a small, thin, 3-axis MEMS accelerometer that provides low power consumption and high resolution measurement up to ±200 g. The digital output...
Datasheet
ADXL375 on Analog.com
ADT7320
Recommended for New Designs
The ADT7320 is a high accuracy digital temperature sensor that offers breakthrough performance over a wide industrial temperature
range, housed in a 4...
Datasheet
ADT7320 on Analog.com
ADP320
Recommended for New Designs
The ADP320 200 mA triple output LDO combines high PSRR, low
noise, low quiescent current, and low dropout voltage in a voltage
regulator ideally suited...
Datasheet
ADP320 on Analog.com
LT3023
Recommended for New Designs
The LT3023 is a dual, micropower, low noise, low dropout regulator. With an external 0.01µF bypass capacitor, output noise drops to 20µVRMS over a 10Hz...
Datasheet
LT3023 on Analog.com
LT3029
Recommended for New Designs
The LT3029 is a dual, micropower, low noise, low dropout linear regulator. The device operates either with a common input supply or independent input supplies...
Datasheet
LT3029 on Analog.com
AD7380
Production
The AD7380/AD7381 are a 16-bit and 14-bit pin-compatible family of dual simultaneous sampling, high speed, low power, successive approximation register...
Datasheet
AD7380 on Analog.com
AD7866
Production
The AD7866 is a dual 12-bit high-speed, low power, successive-approximation ADC. The part operates from a single 2.7 V to 5.25 V power supply and features...
Datasheet
AD7866 on Analog.com
AD7760
Production
The AD7760 is a high performance, 24-bit S-? analog-to-digital converter (ADC). It combines wide input bandwidth and high speed with the benefits of S...
Datasheet
AD7760 on Analog.com
ADA4622-4
Recommended for New Designs
The ADA4622-1/ADA4622-2/ADA4622-4 are the next generation of the AD820/AD822/AD824 single-supply, rail-to-rail output (RRO), precision junction field effect...
Datasheet
ADA4622-4 on Analog.com
LTC6702
Recommended for New Designs
The LTC6702 is an extremely small dual comparator designed to maximize battery life while providing both speed and low voltage operation in applications...
Datasheet
LTC6702 on Analog.com
MAX22506E
Production
The MAX22506E ESD-protected RS-485/RS-422 transceiver
is optimized for high-speed communication up to
50Mbps. This transceiver features integrated hot...
Datasheet
MAX22506E on Analog.com
ADM3066E
Production
The ADM3061E/ADM3062E/ADM3063E/ADM3064E/ADM3065E/ADM3066E/ADM3067E/ADM3068E are 3.0 V to
5.5 V, IEC electrostatic discharge (ESD) protected RS-485
transceivers...
Datasheet
ADM3066E on Analog.com
ADM4168E
Production
The ADM4168E is a dual RS-422 transceiver suitable for high speed communication on point to point and multidrop transmission lines. The ADM4168E is designed...
Datasheet
ADM4168E on Analog.com
MAX22500E
Production
The MAX22500E/MAX22501E half-duplex ESD-protected RS-485/RS-422 transceivers are optimized for high-speed (up to 100Mbps) communication over long cables...
Datasheet
MAX22500E on Analog.com
MAX32672
Recommended for New Designs
In the DARWIN family, the MAX32672 is an ultra-low-power, cost-effective, highly integrated, and highly reliable 32-bit microcontroller enabling designs...
Datasheet
MAX32672 on Analog.com
MAX32662
Recommended for New Designs
In the DARWIN family, the MAX32662 is an ultra-low-power, cost-effective, highly integrated 32-bit microcontroller designed for small battery-powered devices...
Datasheet
MAX32662 on Analog.com
by Richard Anslow and Michael Jackson
The previous blog in this series discussed motor encoder technologies (optical, magnetic) and reviewed critical metrics for specifying an encoder in a robot application. This blog looks at the function and operation of absolute and incremental encoders which are based on these technologies, and discusses the relative advantages and disadvantages of each.
What are Incremental Encoders and How do they Work?
An incremental encoder provides information about the position of a shaft relative to its starting point by producing a stream of binary pulses proportional to the rotational movement. Knowing an encoder's resolution (the total number of pulses per rotation) and counting the pulses generated as the shaft rotates, a controller can calculate its speed and position relative to a fixed reference referred to as 'home'. However, a limitation of single-channel incremental encoders is that they can't determine the direction of a rotating shaft. Determining direction requires a dual-channel design that produces two output pulses ("A" and "B"), 90° out of phase with each other (quadrature), and monitoring which channel goes high first. Incremental encoders are well suited for harsh environments because they are robust in the presence of vibrations. However, a significant drawback is that if a system experiences a temporary power outage, the encoder loses track of where it is relative to its starting point and requires resetting to its 'home' location after power is restored. Resetting can be problematic for some applications like, for example, a robot arm performing precision cutting of a metal sheet, which would be unable to continue from its original position, wasting raw material or potentially causing damage.
Figure 1 Incremental encoder
What are Absolute Encoders and How Do They Work?
An absolute rotary encoder provides exact coordinates for the location of a motor shaft during one (or several) revolutions. Coordinates are represented as fixed digital codes, meaning this encoder type can still maintain a record of the shaft position if power fails. Once returned, the system can immediately resume motion without resetting the shaft to its 'home' location. Absolute encoders use a coded disc to create a unique binary representation of each point during a revolution. As the code's disc rotates, the motor control system periodically reads the code and converts it into a multi-bit digital number. By regularly polling the encoder, the controller can determine the position of the rotating shaft and use multiple readings to calculate its velocity. Even if a system misses a location reading, this is not a problem, as the encoder will provide the changed shaft position at the next reading. Many manufacturers provide standard single-turn encoders with 12- or 16-bit resolution, but higher-end models can resolve up to 22 bits. Tracking more than one shaft rotation requires a multi-turn encoder. These have a secondary disk geared to the primary disk, and the secondary disk code increments each time the primary disk completes a revolution. Multi-turn encoders typically provide coordinates for 4096 (12-bit) unique locations for up to 4096 (12-bit) revolutions.
Figure 2 Absolute encoder
Which Type to Use and Where?
The type of encoder to use depends on the application requirements. Incremental encoders are excellent for monitoring speed and direction. They are also easy to integrate and require little maintenance, making them a good choice for less complex and lower-cost applications like monitoring the speed of conveyors in a factory. Whether the appropriate incremental encoder is a single-channel, or a quadrature depends upon whether the application is direction sensitive. Absolute encoders are more suitable for safety-critical applications like high-performance computer numerical control (CNC) machines. Figure 3 shows a signal-chain block diagram for the commonly used optical-based incremental encoder, while Table 1 provides a list of recommended ICs from Analog Devices for each block.
Figure 3 Signal chain block diagram for an optical-based incremental encoder
|
Component |
Recommended Part Numbers |
|
MEMS Accelerometer |
ADXL371, ADXL372, ADXL314, ADXL375 |
|
Temperature Sensor |
ADT7320 |
|
Power (LDO) |
ADP320, LT3023, LT3029 |
|
ADC, 12-,16-bit, 24 bit |
AD7380, AD7866, AD7760 |
|
Precision Op-Amp |
ADA4622-4 |
|
Dual Comparator |
LTC6702 |
|
Transceiver (RS-485, RS-422) |
MAX22506E, ADM3066E, ADM4168E, MAX22500E |
|
Microcontroller, integrated ADC |
MAX32672, MAX32662 |
Table 1 Recommended ICs from Analog Devices for each block in the signal chain.
The following blog in this series will look at some future trends for motor encoder technologies.
