“There are hidden dangers of jamming, squeezing, and possible injury to the power windows or door devices that can be automatically closed in the car. They must be able to move in the opposite direction to prevent the force applied by the motor from exceeding normal limits. This characteristic means that the speed, current, and position of the glass must be continuously monitored.
There are hidden dangers of jamming, squeezing, and possible injury to the power windows or door devices that can be automatically closed in the car. They must be able to move in the opposite direction to prevent the force applied by the motor from exceeding normal limits. This characteristic means that the speed, current, and position of the glass must be continuously monitored.
Electric equipment in modern cars
At present, Electronic components and systems in high-end passenger cars account for more than 20% of the cost. Increasing the number of electronic devices can better control sensors and actuators, thereby enhancing the comfort and safety of the car. It can be predicted that most middle or high-end cars will be systematically equipped with electric windows or door systems. The vast majority of these devices are fully automatic, which means that they must be accompanied by safety systems to prevent injuries or mechanical failures. There are already laws and regulations that must be followed by electric systems. This is especially true for the lifting of windows and sliding of doors. This application note describes how to implement an anti-pinch algorithm, which was originally used in power window systems, but can be easily transplanted to other movable devices.
Automotive power windows are subject to international standards, such as MVSS118 in the United States or 74/60/EEC in Europe. In terms of how to reduce the risk to children, the requirements of these documents are as follows: detection area: 4mm to 200mm; maximum clamping force is 100N; can be reversed when clamped; determining deflection angle test: 5N/mm to 20N/mm .
About the hardware
The different detection strategies for determining whether there are obstacles in the critical inclusion area are:
(1) No mechanical contact. There is a reaction before the force of the clamping force is applied to the object. Because there is no external force exerted on the object, this is the best way of protection. It also does not rely on vibration, aerodynamic changes or deformation. However, this method requires integrated sensors (infrared, ultrasonic, etc.) and related circuit modules and circuits, resulting in additional costs.
(2) There is mechanical contact. The measured pressure is transmitted to the system to indicate that an object is clamped. In this regard, designers also have two basic techniques available: orientation measurement (mechanical sensors or contactors are integrated into the door seal, these solutions have always been costly and limit the style design of the windows/doors), or Non-directional measurement through physical monitoring (this is an overall cost-optimal solution).
Details of anti-pinch algorithm
The object detection algorithm must meet the requirements of the standard (FMVSS118 & 74/60/EEC) from the beginning: the detection area is 4 to 200 mm; the maximum force is 100 N; the direction is reversed when the object is clamped; the standard confirmation test .
The reasons for having to be self-adapted include: C. The mechanical parts in the lifting system will change over time (aging, local deformation, wear, etc.); C. The electronic characteristics will change greatly; C. The impact of the environment on friction Influence (temperature, humidity, icing, etc.); the system should not respond to disturbances and incorrect detection of inclusions. It must be robust to air friction, road vibration, power failure, etc.
Physical parameters of the solution using the motor
It must be possible to calculate the force exerted on the glass by the current of the motor. In terms of speed, it can continuously provide the position information of the moving parts. These parameters can be used to determine whether an object is encountered and whether the object is in the detection area; whether the applied force exceeds limit
This article describes an anti-pinch algorithm that works by measuring motor current and Hall-effect speed indicators. With very few changes, the algorithm can be used in systems such as sliding doors or roofs.
Inclusion detection algorithm
Under normal circumstances, the operation of the object detection algorithm is through indirect measurement of the window lifting system, including current (torque) and position (speed). Application notes related to algorithms use two techniques, which are based on:
C. Calibration torque stored in conflict-free memory: Perform a preliminary learning sequence and store the torque value in the memory. This technique is very memory intensive and requires a calibration sequence.
C Speed derivation calculation: a very meaningful technique, because it requires less memory, but requires more calculations, and has the advantages of two methods.
Implementation on AVR
The algorithms detailed in the previous paragraphs have been implemented and tested on an AVR ATmega88 development board. Figure 2 describes the hardware used to implement the algorithm. It uses a standard ATmega88 and analog chain to measure the motor current. The hardware has two Hall effect sensors. The direction of the motor is controlled by a two-pole delay, and a field effect tube is used to activate the switch of the motor.
In-system programming Flash
In-system programming allows any AVR microcontroller located in the end system to be programmed and reprogrammed. Through a simple three-wire SPI interface, the in-system programmer performs serial communication with the AVR microcontroller to reprogram all the non-volatile memory on the chip. In-system programming does not require the chip to be physically taken out of the system. This saves time and money whether it is in the development stage of the laboratory or the upgrade of on-site software or parameters. When uploading code into Flash memory in the final product stage, using the same standard AVR Flash microcontroller in multiple applications and custom versions can simplify total management.
All codes are implemented in C language using IAR EWAVR 4.1. The realization of basic functions (position management, initialization, current management, window operation, anti-pinch monitoring) requires 2KB Flash. Add extended functions such as calibration, blocking point detection and storage, and the code size can be expanded to 4KB. The software code is available on Atmel’s website, and its structure is as follows:
The initialization pin changes the interrupt to be used through a Hall-effect sensor (sensitive to the rise and fall of the signal edge). It also initializes the clock and ACD used to measure speed and motor current.
This function loads the window lift parameters from EEPROM or with initial values to initialize the window lifter. These parameters include the size of the car window, sensor value, clipping threshold, clipping area, known last position, etc. If the position parameter is a default value, it can request a descending command to limit the bottom end Initialize the window lifter on the value.
This function saves the window lift parameters into EEPROM.
This function contains the window lift state machine. It controls the operation of the car window through the existing event parameters. Monitor the position of the window, the limits of the rising and falling ends, and the state of the anti-pinch system. Return the state of the window lifter (the same value as the get_window_state function).
This interrupt sub-case is executed on the edge of the Hall sensor. It calculates the rolling direction, position, derived speed and motor current reference value. By calculating continuous direction changes, it can also detect the default value of the Hall effect sensor (the sensor is not connected to an interrupt pin).
This function forces the window to stop after a defined step. The function returns the state of the window lifting state machine (this return value is used in the window_ctrl function).
Establishing the window lift status: used in mandatory operations (such as stop requests…)
Calculate the average value of the last 8 sampling points to filter the motor current.
This function monitors the start button, generates operation command events and passes them to the window_ctrl function.
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