In this Article, you will learn What is Rotary Encoder? What are the types of Rotary Encoders, What is the principle and working of Rotary encoders in detail. You might have searched for Rotary Encoders and read articles about it but the important information which is need might not be shown or unpublished. Which leads to questions rather than answers which you need.
So, in this Article leaving out the non-sense things and follow our explanation in simple terms for how Rotary Encoder works and what are the applications of them.
What is a Rotary Encoder?
A rotary encoder, also known as a shaft encoder, is a sensor that generates an electrical signal in response to rotational movement. This signal is used to determine or control the speed or position of a mechanical device. A rotary encoder is mounted on a cylindrical shaft and is often used in conjunction with mechanical conversion devices, such as linear guides and rack and pinions, to measure linear motion. Rotary encoders are used in a wide variety of precision equipment that requires tight position or speed control, including medical devices, robotics, assembly machines, and test equipment, among others.
Technologies used to build Rotary Encoders?
- Mechanical: Also known as conductive encoders. A series of circumferential copper tracks etched onto a PCB is used to encode the information via contact brushes sensing the conductive areas. Mechanical encoders are economical but susceptible to mechanical wear. They are common in human interfaces such as digital multimeters.
- Optical: This uses a light shining onto a photodiode through slits in a metal or glass disc. Reflective versions also exist. This is one of the most common technologies. Optical encoders are very sensitive to dust.
- On-Axis Magnetic: This technology typically uses a specially magnetized 2 pole neodymium magnet attached to the motor shaft. Because it can be fixed to the end of the shaft, it can work with motors that only have 1 shaft extending out of the motor body. The accuracy can vary from a few degrees to under 1 degree. Resolutions can be as low as 1 degree or as high as 0.09 degree (4000 CPR, Count per Revolution). Poorly designed internal interpolation can cause output jitter, but this can be overcome with internal sample averaging.
- Off-Axis Magnetic: This technology typically employs the use of rubber bonded ferrite magnets attached to a metal hub. This offers flexibility in design and low cost for custom applications. Due to the flexibility in many off axis encoder chips they can be programmed to accept any number of pole widths so the chip can be placed in any position required for the application. Magnetic encoders operate in harsh environments where optical encoders would fail to work.
Types of Rotary Encoders:
Encoders can be divided into two basic types: incremental and absolute encoders.
- Incremental Encoders
- Absolute Encoders
An incremental encoder will immediately report changes in position, which is an essential capability in some applications. However, it does not report or keeps track of the absolute position. As a result, the mechanical system monitored by an incremental encoder may have to be moved to a fixed reference point to initialize the position measurement.
The distinguishing feature of an incremental encoder is that it indicates a change in angle. That is, when an incremental encoder is turned on, it does not indicate its angular position until it is given a reference point from which it measures it.
An absolute encoder maintains position information when power is removed from the encoder. The position of the encoder is available immediately on applying power. The relationship between the encoder value and the physical position of the controlled machinery is set at assembly; the system does not need to return to a calibration point to maintain position accuracy.
An absolute encoder has multiple code rings with various binary weightings which provide a data word representing the absolute position of the encoder within one revolution. This type of encoder is often referred to as a parallel absolute encoder.
A multi-turn absolute rotary encoder includes additional code wheels and gears. A high-resolution wheel measures the fractional rotation, and lower-resolution geared code wheels record the number of whole revolutions of the shaft.
An absolute encoder unambiguously indicates its position within a scale or range. That is, when an absolute encoder is turned on, it indicates its angular position without the need for a reference or motion point.
How Rotary Encoder Works?
The encoder has a disk with evenly spaced contact zones that are connected to the common pin C and two other separate contact pins A and B, as illustrated below.
When the disk will start rotating step by step, pins A and B will start making contact with the common pin and the two square wave output signals will be generated accordingly.
Any of the two outputs can be used for determining the rotated position if we just count the pulses of the signal. However, if we want to determine the rotation direction as well, we need to consider both signals at the same time.
We can notice that the two output signals are displaced at 90 degrees out of phase from each other. If the encoder is rotating clockwise output A will be ahead of output B.
So if we count the steps each time the signal changes, from High to Low or from Low to High, we can notice at that time the two output signals have opposite values. Vice versa, if the encoder is rotating counter-clockwise, the output signals have equal values. So considering this, we can easily program our controller to read the encoder position and the rotation direction.
What is the resolution of a rotary encoder?
The resolution of a rotary encoder corresponds to the maximum number of points it can measure during one revolution. For an incremental encoder, the resolution is directly related to the number of pulses it outputs per revolution. For an absolute encoder, it is related to the number of encoding bits . For example, a 16-bit encoder will have a resolution of 65,536 points per turn.
The choice of encoder resolution is made based on the expected resolution for the application and the precision of the mechanical components that make up the measurement chain. The encoder is connected to an electronic device, controller or counter, which tolerates a maximum input frequency that must be met. In fact, a high resolution incremental encoder provides a higher number of pulses in one turn than a low resolution incremental encoder. Depending on the rotation speed imposed by the application, the encoder output signal may have a higher frequency than the device connected to the encoder is capable of supporting. In this case, a rotary encoder with a lower resolution should be used.
Applications of Rotary Encoders:
- Door control devices.
- Lens beveling machines.
- Testing machines.
- Ultrasonic welding.
- Warping machines and medical technical equipment.
- Parts assembly machines.
- Labeling machines.
- Graphical displays of X and Y axes.
- Analysis systems.
- Drilling machines.
- Mixing machines.
Advantages & Disadvantages of Rotary Encoders:
Advantages of an Encoder
- Highly reliable and accurate
- Low-cost feedback
- High resolution
- Integrated electronics
- Fuses optical and digital technology
- Can be incorporated into existing applications
- Compact size
Disadvantages of an Encoder
- Subject to magnetic or radio interference (Magnetic Encoders)
- Direct light source interference (Optical Encoders)
- Susceptible to dirt, oil and dust contaminates
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