Les codeurs optiques

Summary

This video explains the functioning of optical encoders, which are used to measure the angular position of an object. It covers two main types of encoders: incremental and absolute. The incremental encoder works by counting pulses from a light beam interrupted by a rotating disk, allowing the calculation of the object's position. The absolute encoder, on the other hand, uses multiple tracks and provides unique positions for each angle without needing resets. The video also discusses the resolution, accuracy, and advantages/disadvantages of each type, highlighting their applications and importance in industrial automation.

Takeaways

• 😀 Optical encoders are used to measure angular positions in machines, such as CNC lathes, with high precision.
• 😀 An optical encoder works by using a disk with tracks (A, B, Z) that emit light beams, generating electrical pulses when interrupted.
• 😀 The A and B tracks provide signals in quadrature, allowing detection of both the position and the direction of rotation.
• 😀 The Z track provides one pulse per full rotation, helping to count the number of complete turns.
• 😀 The precision of an incremental encoder is determined by the number of pulses per revolution; for example, 16 pulses correspond to a 22.5-degree precision.
• 😀 The angular position of the tool in an incremental encoder system can be calculated by counting the pulses from the A and B tracks.
• 😀 The absolute encoder uses multiple tracks to give an absolute position value at any given time, unlike incremental encoders that rely on counting pulses from a reference.
• 😀 Absolute encoders are more expensive and complex than incremental encoders but offer better reliability since they don't require reset after power loss.
• 😀 The resolution of an absolute encoder is calculated as 2 raised to the power of the number of tracks (n), providing a high level of precision.
• 😀 A significant advantage of absolute encoders is their insensitivity to power loss, as they retain position information without needing reinitialization.
• 😀 While incremental encoders are simpler and cheaper, absolute encoders are preferable in applications where maintaining absolute position is crucial and power interruptions are a concern.

Q & A

What is an optical encoder?

An optical encoder is a device that measures angular position using light sensors to detect interruptions caused by patterns on a rotating disk, providing a digital output representing the position.

How do incremental encoders work?

Incremental encoders work by generating pulses as a disk rotates. Each pulse corresponds to a specific angular position, and the number of pulses is counted to determine the position. These encoders are typically used for measuring rotations from a reference point.

What are the key components of an optical encoder?

The key components of an optical encoder include a rotating disk with multiple tracks (often including A, B, and Z tracks), light emitters, and receivers that detect the interruptions in the light beam caused by the disk's patterns.

What is the purpose of the Z track in an optical encoder?

The Z track in an optical encoder is used to count the number of full rotations of the disk. It generates a unique pulse for each complete revolution, serving as a reference to reset the count for subsequent measurements.

How is angular precision calculated in an incremental encoder?

Angular precision in an incremental encoder is calculated by dividing 360° by the number of pulses per rotation (the number of points). This determines the smallest measurable angle of rotation for the encoder.

What is the difference between the A and B tracks in an incremental encoder?

The A and B tracks in an incremental encoder are offset by 90 degrees in phase. This allows for the detection of rotation direction by comparing the timing of the signals from both tracks.

What are the advantages of absolute encoders over incremental encoders?

Absolute encoders provide a unique position reading for every angle of rotation, eliminating the need to reference the position after power loss. They are more reliable in applications where uninterrupted position tracking is essential.

What is the resolution of an absolute encoder?

The resolution of an absolute encoder is determined by the number of tracks on the encoder disk, calculated as 2^n, where n is the number of tracks. The precision is the smallest angular movement that the encoder can detect.

What is the main disadvantage of absolute encoders compared to incremental encoders?

The main disadvantage of absolute encoders is that they are more expensive, larger, and require more input channels for processing, making them less cost-effective for some applications.

How does an absolute encoder differ from an incremental encoder in terms of power loss handling?

An absolute encoder retains its position even during power loss, as each position corresponds to a unique output. In contrast, an incremental encoder loses its position information during power loss and must be recalibrated or referenced.