What is an Encoder?

1. What is an Encoder?

“Encoder” is classified as electronic components using sensors to detect mechanical movement, direction, and angle, and output the information as electrical signals.

Encoders are widely used in various industries such as machine tools, industrial robots, and act as high-precision position control sensors. In recent years, reflective encoders have been used in ultra-compact actuators and collaborative robots that require a small footprint.

 

2. Types of Encoders

Encoders are classified according to 1) Detection method of electrical signals, 2) Detection target, and 3) Output method.

1) Detection method of electrical signals

Optical encoders

This type of encoder uses an optical sensor to detect whether light is on or off. This encoder characterized by its ability to handle high precision and high magnetic fields.

Optical encoders include reflective, transmissive, and diffraction grating types. Since ultra-thin stainless-steel plates or glass disks are used as rotating discs, mechanical vibration and shock may be a problem.

Magnetic encoders

This type of encoders uses a magnetic sensor to detect changes in the magnetic field. This encoder has a simple and compact design and high durability.

Magnetic encoders combine a magnetic drum with a magnetoresistive element or other magnetoelectric conversion element. In addition, they have a structure that is easy to increase mechanical strength.

2) Detection target

Linear encoders

This is a type of encoder that measures linear shaft movement and outputs it as position information.

One of the typical applications is a sensor that detects translational displacement by recording a sinusoidal magnetic pattern of a certain wavelength on a scale and measuring the magnetic signal with a magnetic flux response head.

Other methods have also been developed, such as those that use an optical sensor to detect a slit pattern instead of a magnetic pattern, and those that use capacitance change.

Rotary encoders

This is a type of encoder that measures the rotational movement (angle) and outputs it as position information.

This type of encoder is often used as a sensor in robotics. It reads graduations evenly spaced on a disc. This encoder is considered to be a rounded version of linear scale, and the same technology is used for manufacturing this product.

They are used in a variety of applications, from inexpensive devices built into printers to high-precision control and measurement devices.

3) Output method

Incremental type

This type of encoder measures the disc rotation angle by converting the number of detected pulses. It also calculates the rotation speed from the pulse interval or the number of pulses in a unit time.

Incremental types only detect the change in the disc rotation. Strictly speaking, it detects the change in the sensor output from the reference position, and stores the information in a counter or memory.

Absolute type

The absolute type outputs the absolute value of the rotation angle. It detects the mechanical position of a disc immediately after power-on.

While the incremental type outputs only the incremental value and requires the origin to be aligned, the absolute type has a one-to-one correspondence between the disk angle and the output code.

Thus, the absolute type doesn’t require adjusting origin. However, the scale pattern is more complicated, and the resolution tends to be lower than that of the incremental type.

3. Where are encoders used?

Joints of Robot Arm

 

There are many types of mechanical position/posture sensors, but generally, manufacturers in robotics industry use articulated arms with rotary encoders placed at the joints.

It is necessary to use either a 3-DOF type that measures only position or a 6-DOF type that measures both position and posture depending on the number of joints to be measured.

In some special case, there is also a motion capture device with encoders placed at the positions corresponding to the joints of the human body to measure its movement.

Doors of Elevator

There is a motor controlling opening and closing the elevator door, and it requires low noise due to the close proximity of passenger.

There is an encoder used in the motor which controls the speed of the door movement. It also helps to determine the position of the doors.

Printers

Encoders are used to control the operation of ink heads of inkjet printers.

The encoder sends pulse signals to the industrial inkjet printer as the attached pulley rotates. The inkjet printer uses the interval between the pulse signals to recognize the speed of the object.

The use of an encoder in the printer makes it possible to print beautifully an accurately. Encoders are also used to control the rotating drum that moves the paper.

Machine tools

Encoders are used to control the horizontal movement of the table where the workpiece is placed.

For example, NC milling machines and electrical discharge machines require finishing accuracy in the range of a few microns to a few tens of microns. To achieve this, they require encoders with a resolution about 10 times higher than the required finishing accuracy.

4. How does an encoder work?

Photo-interrupter

In this section, we will explain the principle of encoder operation using an optical transmission rotary encoder as an example.

This type of encoder mainly consists of a light source (on the infrared LED side), a light receiving element (on the photo IC side), and an encoder disc. The encoder disk is engraved with bars that serve as scales.

The encoder disk, which is used to measure the number of rotations of the motor, is mounted between the U-shaped parts shown in the illustration. This U-shaped part is called a “photo interrupter”.

The photo interrupter contains an infrared LED and a photo IC placed between the discs. When infrared light is irradiated, this mechanical part measures the number of times the LED light passes through the bar hole of the disc.

The number is converted into an angle to detect the rotation angle and speed of the disc.

5. How to choose an encoder

【Step 1】 Model (Rotary or Linear?)

The first step in selecting an encoder is to decide whether to use a rotary or a linear encoder.

You can select an encoder based on whether the final motion of the drive system will be linear or rotary.

【Step 2】 How to detect the electrical signal (Optical or Magnetic?)

Magnetic encoders detect changes in the magnetic field and therefore have the advantage of being environmentally resistant and resistant to contamination by dust, oil and water. For this reason, magnetic encoders are suitable for use in dusty, oily, or watery environments.

Optical encoders, on the other hand, have the advantage that their accuracy and resolution can be easily improved by customizing the shape of the bar. In addition, since they are not affected by the surrounding magnetic field, they can be used under a strong magnetic field environment.

【Step 3】 Output method (Incremental or Absolute?)

The resolution is the same for both absolute and incremental.

The absolute type provides absolute position information even when the power is turned off. Therefore, it does not require home positioning.

On the other hand, incremental types require various sensors for home positioning, which can be costly. However, the incremental type is simply structured and is relatively inexpensive. Also, this type is suitable for measuring speed and motion direction.

【Step 4】 Resolution and specification (Does it have appropriate Size and Resolution?)

When choosing the resolution of encoders, it is common to select a resolution that provides 1/2 to 1/4 of the total mechanical system accuracy.

Their dimensions should be determined according to the system in which they are incorporated. This means that you need to measure the housing diameter, length, and output shaft diameter when choosing the size of encoders.

If you cannot find an off-the-shelf encoder with the appropriate resolution and size, consider making a custom one.

6. Our specialty

We produce Optical Encoder Disks and Optical Linear Encoder Strips, which are essential for motion controlling technology and are currently used in many applications as follows.

  • Industrial robotics
  • Positioning servos
  • Factory automation
  • Auto industry

The “Encoder Disk” is a disc-shaped scale built into a rotary encoder device .

The “Linear Encoder Strip is a linearly shaped scale that is incorporated into an encoder device detecting the position of a linear axis and outputs it as position information.

Here are our products

Optical Encoder Disk
Optical Linear Encoder Strip
PAGE TOP