In astronomy, when scientists use large telescopes to track stars, the telescope needs to choose the right encoder to achieve a certain speed control accuracy. However, the encoder requirements are very high at this time, for example, when the star speed is 0.004%, the resolution of 26-bit encoder is required to meet the speed measurement requirements.
In addition, there are elevator-specific encoders, machine-specific encoders, servo motor-specific encoders and so on, it can be said that encoders are everywhere.
From stepper motors to intelligent systems, how do encoders choose?
So what exactly is an encoder?
By definition, an encoder is a device that compiles signals (such as bitstreams) or data and converts them into signals that can be used for communication, transmission, and storage.
A simple understanding is to convert signals that humans cannot directly understand into signals that we humans can directly understand, so that we can dictate devices or devices.
In addition, there are elevator-specific encoders, machine-specific encoders, servo motor-specific encoders and so on, it can be said that encoders are everywhere.
From stepper motors to intelligent systems, how do encoders choose?
So what exactly is an encoder?
By definition, an encoder is a device that compiles signals (such as bitstreams) or data and converts them into signals that can be used for communication, transmission, and storage.
A simple understanding is to convert signals that humans cannot directly understand into signals that we humans can directly understand, so that we can dictate devices or devices.
The encoder can be divided into incremental, absolute and hybrid according to the scale method and signal output form.
Incremental and absolute are common, but the difference between the two has become a problem for the vast number of users.
Therefore, only incremental and absolute comparisons are made here, allowing users to make a better choice when choosing in the future.
First, the two work differently:
1, incremental encoder works:
An incremental encoder converts a displacement into a periodic electrical signal, which is then converted into a counting pulse, representing the size of the displacement by the number of pulses.
Take pour water to describe, incremental encoder is like, find a cup that does not know the size and then pour water into it, when poured full once, empty the cup once, and then pour water, and finally according to the number of times the cup is poured to calculate the distance.
Structurally, incremental encoders consist of connection shafts, code disks, light sources, and output circuits. In fact, the encoder is basically this composition, the following is no longer repeated.
The incremental encoder obtains four sets of sine wave signals from the photoelectronic transmitter and receiver devices, which are combined into A, B, C and D, each with a difference of 90 degrees and four sets with a difference of 360 degrees (i.e., one week wave). The C and D signals are reversed and superimposed on the A and B phases, thus enhancing the role of the stable signal; In addition, a Z-phase pulse is output per revolution to represent the zero reference bit.
Because A, B two phases before and after the difference of 90 degrees, so you can compare A, B two phases which come to judge the positive and reverse encoder.
The zero reference bit of the encoder can be obtained by the zero pulse. The distance and angle aresods are calculated by zero reference bits and the number of pulses.
2, absolute encoder works
There are many lines on the code plate of the absolute encoder to arrange every position on the encoder. Because each location is different, you want to know the displacement size, as long as you know the starting and terminating positions, you don't have to count like an incremental encoder.
Or take pouring water as an example, absolute encoder is like looking for a scaled, higher cup, pouring water into it, and finally calculating the distance based on the start and end scales.
Structurally, there are many optical channels on the absolute encoder optical code disk, each with 2 lines, 4 lines, 8 lines, 16 lines... Orchestration, so that anywhere in the encoder, you can get a set of unique binary encodings (gray codes) from the zero-square of 2 to the n-1 side of the n-1 side by reading the pass and dark of each line, which is also the n-bit absolute encoder.
Such encoders are determined by the mechanical position (start and end position) of the photocode disk and are therefore not affected by power outages or external interference, which is one of the excellent characteristics of absolute encoders.
Because of this feature, absolute encoders do not need to remember, do not need to find zero reference points, and do not have to count all the time, therefore, the anti-jamming characteristics of the encoder, data reliability has been greatly improved.
Based on the construction of an absolute encoder, it is bound to face a problem: counting to the maximum value.
In order to solve this problem, a multi-circle absolute encoder has emerged.
For multi-circle absolute encoders, there are three common design options:
First, inside the encoder, multiple axes are coupled with mechanical gears to calculate the total number of turns.
Take the example of pouring water, that is, the previously mentioned scaled cup, when the cup is full, and then find a scaled, larger cup, pour the water in the small cup into the large cup, the last size of the cup to calculate the distance.
The second is to use electronic counters and capacitors to calculate the total number of turns.
From stepper motors to intelligent systems, how do encoders choose?
Or take the example of pouring water, this time when the scaled cup is full, pour out the water, while using a counter to measure the number of times the pour is full, and finally by the counter and the cup add up to calculate the distance.
Third, in some magnetic encoders, the Wigan gold line is used and the Wigan effect is used to count.
All three methods come at a cost, for example, the first, because of the use of mechanical gears, which can cause wear and tear on the encoder, resulting in reduced accuracy.
As for the scheme that constitutes a multi-circle absolute encoder, there is not much to describe here, and interested friends can go to consult the relevant information.
There are two very big differences between the two because of the difference in working principle and mechanical composition:
1, power-off memory is different
Incremental encoder has no memory, power-off restart must return to reference zero, in order to find the required position, each power-off to start again.
The most common incremental encoder is the positioning of the printer scanner, every time the printer is turned on, we can hear a crackling sound, in fact, this is the printer looking for reference zero points, after which to work.
The absolute encoder has a memory, the power-off restart does not need to go back to zero, you can know where the target is located. This makes absolute encoders undisturbed in the process, and their anti-jamming properties and data reliability are greatly improved.
2, the code plate is different
Because the two count differently, the code plates are also very different.
The difference between a code disk is one of the biggest differences between an absolute encoder and an incremental encoder.
In addition to the above differences, there are many small differences between absolute encoders and incremental encoders:
3, the output signal is different
The incremental encoder outputs a pulsed signal, while the absolute encoder outputs a set of binary values.
4, the number of limited different
The number of incremental encoders is unlimited, and absolute encoders cannot exceed the range of increments.
5, the application area is not exactly the same
The use of breakpoint memory makes incremental encoders and absolute encoders very different in the field of application, incremental encoders are more suitable for determining speed, distance or direction of motion, and absolute encoders are more and more widely used in the field of industrial positioning due to their characteristics.
6, the price is not the same
Due to the excellent quality of absolute encoders, the price is higher than that of incremental encoders.
With the difference between the two, let's look at what you need to be aware of when choosing an encoder:
Whether a power outage is required to hold
Absolute encoders must be used in cases where continuous checks are required.
The required measurement accuracy
In contrast, absolute encoders are more accurate than incremental encoders.
Resolution
The resolution of the encoder, i.e. the number of pulses output by the encoder when the motor rotor shaft is rotated one turn. The resolution is one of the most critical factors affecting the speed measurement effect.
The maximum speed required
The speed measurement method of encoder is divided into three categories: T method, N method and M/T method.
Generally speaking, the T method has the best speed measurement effect in the low speed zone, and the M method is better than the T method in the high speed zone. Although the M/T method is implemented much higher than the M and T methods, in most cases, its speed measurement accuracy is also better than the other two.
The required disk material
The encoder code plate is made of glass, metal and plastic.
From stepper motors to intelligent systems, how do encoders choose?
Glass code plate is a very thin line deposited on the glass, its thermal stability is good, high precision.
Metal code plate directly to pass and not through the line, not easy to break, but because the metal has a certain thickness, accuracy may be affected, its thermal stability is much worse than glass.
Plastic code disk is economical, its cost is low, but accuracy, thermal stability, life is worse.
In addition to the factors listed above, the choice of encoder, there are many other factors, specifically based on the use of the occasion and environment to make a choice.
The best option is to communicate directly with the manufacturers and communicate their needs and concerns to them, and they will give good advice. At that point, you can consider their suggestions based on your knowledge.
Incremental and absolute are common, but the difference between the two has become a problem for the vast number of users.
Therefore, only incremental and absolute comparisons are made here, allowing users to make a better choice when choosing in the future.
First, the two work differently:
1, incremental encoder works:
An incremental encoder converts a displacement into a periodic electrical signal, which is then converted into a counting pulse, representing the size of the displacement by the number of pulses.
Take pour water to describe, incremental encoder is like, find a cup that does not know the size and then pour water into it, when poured full once, empty the cup once, and then pour water, and finally according to the number of times the cup is poured to calculate the distance.
Structurally, incremental encoders consist of connection shafts, code disks, light sources, and output circuits. In fact, the encoder is basically this composition, the following is no longer repeated.
The incremental encoder obtains four sets of sine wave signals from the photoelectronic transmitter and receiver devices, which are combined into A, B, C and D, each with a difference of 90 degrees and four sets with a difference of 360 degrees (i.e., one week wave). The C and D signals are reversed and superimposed on the A and B phases, thus enhancing the role of the stable signal; In addition, a Z-phase pulse is output per revolution to represent the zero reference bit.
Because A, B two phases before and after the difference of 90 degrees, so you can compare A, B two phases which come to judge the positive and reverse encoder.
The zero reference bit of the encoder can be obtained by the zero pulse. The distance and angle aresods are calculated by zero reference bits and the number of pulses.
2, absolute encoder works
There are many lines on the code plate of the absolute encoder to arrange every position on the encoder. Because each location is different, you want to know the displacement size, as long as you know the starting and terminating positions, you don't have to count like an incremental encoder.
Or take pouring water as an example, absolute encoder is like looking for a scaled, higher cup, pouring water into it, and finally calculating the distance based on the start and end scales.
Structurally, there are many optical channels on the absolute encoder optical code disk, each with 2 lines, 4 lines, 8 lines, 16 lines... Orchestration, so that anywhere in the encoder, you can get a set of unique binary encodings (gray codes) from the zero-square of 2 to the n-1 side of the n-1 side by reading the pass and dark of each line, which is also the n-bit absolute encoder.
Such encoders are determined by the mechanical position (start and end position) of the photocode disk and are therefore not affected by power outages or external interference, which is one of the excellent characteristics of absolute encoders.
Because of this feature, absolute encoders do not need to remember, do not need to find zero reference points, and do not have to count all the time, therefore, the anti-jamming characteristics of the encoder, data reliability has been greatly improved.
Based on the construction of an absolute encoder, it is bound to face a problem: counting to the maximum value.
In order to solve this problem, a multi-circle absolute encoder has emerged.
For multi-circle absolute encoders, there are three common design options:
First, inside the encoder, multiple axes are coupled with mechanical gears to calculate the total number of turns.
Take the example of pouring water, that is, the previously mentioned scaled cup, when the cup is full, and then find a scaled, larger cup, pour the water in the small cup into the large cup, the last size of the cup to calculate the distance.
The second is to use electronic counters and capacitors to calculate the total number of turns.
From stepper motors to intelligent systems, how do encoders choose?
Or take the example of pouring water, this time when the scaled cup is full, pour out the water, while using a counter to measure the number of times the pour is full, and finally by the counter and the cup add up to calculate the distance.
Third, in some magnetic encoders, the Wigan gold line is used and the Wigan effect is used to count.
All three methods come at a cost, for example, the first, because of the use of mechanical gears, which can cause wear and tear on the encoder, resulting in reduced accuracy.
As for the scheme that constitutes a multi-circle absolute encoder, there is not much to describe here, and interested friends can go to consult the relevant information.
There are two very big differences between the two because of the difference in working principle and mechanical composition:
1, power-off memory is different
Incremental encoder has no memory, power-off restart must return to reference zero, in order to find the required position, each power-off to start again.
The most common incremental encoder is the positioning of the printer scanner, every time the printer is turned on, we can hear a crackling sound, in fact, this is the printer looking for reference zero points, after which to work.
The absolute encoder has a memory, the power-off restart does not need to go back to zero, you can know where the target is located. This makes absolute encoders undisturbed in the process, and their anti-jamming properties and data reliability are greatly improved.
2, the code plate is different
Because the two count differently, the code plates are also very different.
The difference between a code disk is one of the biggest differences between an absolute encoder and an incremental encoder.
In addition to the above differences, there are many small differences between absolute encoders and incremental encoders:
3, the output signal is different
The incremental encoder outputs a pulsed signal, while the absolute encoder outputs a set of binary values.
4, the number of limited different
The number of incremental encoders is unlimited, and absolute encoders cannot exceed the range of increments.
5, the application area is not exactly the same
The use of breakpoint memory makes incremental encoders and absolute encoders very different in the field of application, incremental encoders are more suitable for determining speed, distance or direction of motion, and absolute encoders are more and more widely used in the field of industrial positioning due to their characteristics.
6, the price is not the same
Due to the excellent quality of absolute encoders, the price is higher than that of incremental encoders.
With the difference between the two, let's look at what you need to be aware of when choosing an encoder:
Whether a power outage is required to hold
Absolute encoders must be used in cases where continuous checks are required.
The required measurement accuracy
In contrast, absolute encoders are more accurate than incremental encoders.
Resolution
The resolution of the encoder, i.e. the number of pulses output by the encoder when the motor rotor shaft is rotated one turn. The resolution is one of the most critical factors affecting the speed measurement effect.
The maximum speed required
The speed measurement method of encoder is divided into three categories: T method, N method and M/T method.
Generally speaking, the T method has the best speed measurement effect in the low speed zone, and the M method is better than the T method in the high speed zone. Although the M/T method is implemented much higher than the M and T methods, in most cases, its speed measurement accuracy is also better than the other two.
The required disk material
The encoder code plate is made of glass, metal and plastic.
From stepper motors to intelligent systems, how do encoders choose?
Glass code plate is a very thin line deposited on the glass, its thermal stability is good, high precision.
Metal code plate directly to pass and not through the line, not easy to break, but because the metal has a certain thickness, accuracy may be affected, its thermal stability is much worse than glass.
Plastic code disk is economical, its cost is low, but accuracy, thermal stability, life is worse.
In addition to the factors listed above, the choice of encoder, there are many other factors, specifically based on the use of the occasion and environment to make a choice.
The best option is to communicate directly with the manufacturers and communicate their needs and concerns to them, and they will give good advice. At that point, you can consider their suggestions based on your knowledge.