Working Principle of Encoder for Revolving Door Positioning |TSTC

All automatic revolving doors from TSTC adopt Encoder for positioning, that’s also the reason why the door wings of our revolving doors always start or stop at the precise position. Here is a detailed explanation about how the encoder works .

I. Overview of Core Functions

Revolving doors rely on rotary encoders to collect real-time signals of spindle rotation angle, rotating speed and revolution count. The encoders convert mechanical rotation into electrical signals and transmit them to the controller, which feeds back the door wing position throughout operation. This enables high-precision positioning for start-stop, speed regulation, position locking after arrival, anti-pinch reset and automatic alignment, eliminating door wing misalignment, frame collision and parking position deviation.

II. Basic Structural Matching

1. Mounting Position: Installed synchronously on the drive motor spindle or reduction output spindle of the revolving door, rotating coaxially and synchronously with the door wings.

2. Common Types: Incremental encoder (for basic speed measurement and positioning) + Absolute encoder (stores accurate position after power cut, standard configuration for high-end revolving doors).

3. Supporting Components: Door control PLC / dedicated driver, limit origin sensor sheet, servo motor.

III. Complete Working Process of Precise Positioning

1. Origin Calibration (Zero Positioning upon Power-On)

After the equipment is powered on, the encoder cooperates with the origin photoelectric switch to complete zero calibration, and the controller records the standard stop reference position of the door wings.

– Advantages of absolute encoder: The current door wing position will not be lost after power failure. There is no need to re-search the origin, and the door wing angle can be accurately identified directly after startup.

– Incremental encoder: Position data will be lost after restart, and the door body needs to rotate automatically at low speed to search the origin for reset.

2. Real-Time Angle Acquisition to Track Door Wing Position Continuously

As the door rotates, the grating inside the encoder cuts light and outputs continuous pulse signals:

– Pulse quantity = rotation angle

– Pulse frequency = door wing rotating speed

– Positive/negative pulse = forward/reverse rotation

The controller reads pulse values thousands of times per second to convert the real-time angle of door wings (0°~360°), and keeps track of the current stop position of each door wing at all times.

3. Zoned Precision Speed Control & Smooth Parking Positioning

The operation of revolving doors is divided into four phases: acceleration, constant speed, deceleration and parking, all under closed-loop control based on encoder signals.

– Deceleration Prediction: When the encoder detects that the door wing is a fixed angle away from the standard stop position, the controller immediately sends a deceleration command to slow down the motor, preventing overshoot of the target position due to inertia.

– Precise Position Locking: When the encoder pulse value matches the preset stop angle (entrance alignment or closed partition position), the controller immediately cuts off drive output and locks the spindle via the electromagnetic brake. The door wings stop steadily without offset, ensuring uniform gaps and perfect alignment between door leaves and the frame.

4. Safety Linked Positioning (Anti-Pinch & Anti-Collision Protection)

If people or obstacles block the door wings, the encoder detects a sharp drop in pulse speed. The controller recognizes the stall signal and immediately reverses the door wings to retreat slightly to release the pinched area.

After an emergency stop caused by faults, the encoder records the shutdown angle. Upon restart, the door wings automatically fine-tune to return to the original position, avoiding asymmetric or half-offset door wings.

5. Synchronous Equal Division Positioning for Multi-Leaf Doors

For 3-wing and 4-wing revolving doors, the encoder calculates equal division angles (120° for 3-wing doors, 90° for 4-wing doors). The controller controls startup and shutdown strictly according to these angle intervals to guarantee uniform spacing between door wings and a centered, aligned passage at all times.

IV. Core Advantages of Encoder-Based Precise Positioning

1. High Precision: Pulse subdivision achieves positioning error as low as 0.1°, resulting in minimal parking offset, neat appearance and superior sealing performance.

2. Closed-Loop Feedback with Zero Cumulative Error: The motor rotation volume is corrected continuously in real time, so no gradual positional drift occurs during long-term continuous operation.

3. Power-Off Memory (Absolute Encoder): After power failure or manual emergency push reset, the system automatically retrieves the standard parking position on restart.

4. Intelligent Speed Regulation & Buffering: Pre-deceleration based on angle prediction delivers shock-free, vibrationless start and stop for enhanced user comfort.

5. Fundamental Support for Safety Protection: Position signals enable anti-pinch, anti-collision and reverse rotation prevention logic to prevent accidental door wing movement and injuries.