A、 The forced deceleration device is malfunctioning. When the elevator loses control and rushes towards the top or bottom of the shaft, the first thing it passes through is the forced deceleration switch. If this switch fails or the deceleration relay head is stuck and not released, the elevator cannot decelerate before reaching the end station, that is, the car still runs at a constant speed until squatting or rushing to the top;

B、 The position switch is malfunctioning. If the forced deceleration switch fails to slow down or stop the elevator, especially when the elevator crosses the bottom level with full load, the lower limit switch will fail and the control circuit cannot be disconnected to apply the brake. Even if the limit switch is effective, the elevator will still experience a squatting accident. Therefore, when the elevator reaches the limit switch position, the distance between the car collision plate and the top surface of the buffer is only 150mm~200mm.

Can the car be smoothly stopped within this limited distance? From a kinematic perspective, the braking distance is mainly determined by the magnitude of the braking force of the inertia of the moving object. Assuming that the braking force remains constant, the greater the inertia, the slower the braking deceleration and the longer the braking distance. For an elevator that is fully loaded and descending without deceleration, it is impossible to stop the car without causing a squatting accident

C、 The switch is malfunctioning. Under the condition that both the forced deceleration switch and the limit switch fail, if the limit switch fails, accidents such as squatting or toppling will be inevitable;

D、 The adhesion or slow release of the directional contactor causes the brake to not hold or the holding time to lag.

2. Insufficient braking torque

The braking performance of the brake is an important indicator for the safe operation of elevators. GB10060 stipulates that "reliable braking" is required during traction capacity checks, operational tests, and overload tests.

A、  The brake release clearance is too large;

B、  Adjust the brake pad in a timely manner after the brake shoe wears out, i.e. the spring force is too small;

C、  There is oil stains on the brake wheel and brake shoe surface.

These factors have varying degrees of impact on the occurrence of dangerous situations in elevators. If one of these factors is severe and the elevator is in a state of full load down or empty load up, regardless of whether there are electrical or mechanical safety devices, squatting or toppling may occur.

3. Insufficient gravity

One of the important guarantee conditions for the safe operation of a traction elevator is the friction between the traction rope groove and the traction rope. If the friction is insufficient, even if the brake is reliable, the car cannot stop reliably because the safety device only prevents accidental car falls and dangerous acceleration.

Reasons for insufficient drag force:

A、  Worn groove or reduced diameter of traction rope. Due to the fact that friction is not a constant throughout the entire lifespan of an elevator. With the wear of the rope groove and the continuous reduction of the rope diameter, the traction rope gradually approaches the bottom of the groove, causing the clamping force between the traction rope and the cutting point of the rope groove (for V-shaped traction rope grooves) to gradually decrease, resulting in insufficient friction force;

B、  The diameter of the traction wheel pitch is uneven. During the ascent of the elevator car, the traction rope wound on the groove with a larger pitch diameter has a higher circumferential speed than the traction rope wound on the groove with a smaller pitch diameter, resulting in an increase in tension. Due to the uneven tension of each traction rope, the contact pressure between the traction rope and the groove is different, that is, the tension ratio of each traction rope is too different, and the sliding amount of the traction rope also increases;

C、  The wrap angle of the traction rope on the traction wheel groove is smaller than the design requirement;

D、  The reprocessing of the newly replaced traction rope and traction rope groove does not match the original design.

4. The balance coefficient does not comply with the standard requirement of Gb10058: the balance coefficient of various elevators is 40%~50%. During the elevator's ascent and descent, the counterweight and the car should work in a balanced state as much as possible. Otherwise, it will increase the load on the motor, cause heating and damage to the motor coil, and also affect the safety performance of the car's leveling or operation. As is well known, the traction rope of an elevator must be greater than the difference between the car and the load on the counterweight side in order for the elevator to operate normally.

4. Speed limiter malfunction

A、 The electrical safety switch of the speed limiter is malfunctioning. After the elevator exceeded the speed limit, the control circuit was not disconnected and the brake was not applied;

B、 The mechanical switch of the speed limiter is malfunctioning;

C、 Although the speed limiter operates, it cannot control the action of the car safety clamp. The reason is that the wear of the speed limiter wheel groove reduces the friction between the pulley and the speed limiter rope. When the elevator exceeds the speed limit, although the speed limiter operates, the tension of the speed limiter cannot make the safety clamp work;

D、 The speed regulating part of the speed limiter has become loose. This phenomenon usually does not occur.

6. Safety pliers malfunction

A、 After the installation or maintenance of the safety gear, if it is not tested and adjusted, it may not reach the effective operating position or the safety gears on both sides cannot move synchronously. There is a sequence between the safety clamp on one side of the car catching the guide rail and the safety clamp on the other side of the car catching the guide rail, or the gap between the safety clamp wedge on one side of the car and the side of the guide rail is too large, and the safety clamp on that side fails to stop the car, causing the car to fall;

B、 The surface friction coefficient of the sliding wedge block of the safety clamp decreases. If the actual friction force between the safety clamp wedge block and the side of the guide rail after the action of the safety clamp is less than the force required to act on the guide rail during the action of the safety clamp;

C、 The dirt and rust on the safety gear machinery have not been repaired and cleaned in a timely manner; The selection of safety clamps does not comply with national standards for elevator speed;

In addition, failure to comply with the rated load capacity (number of members) of the elevator results in severe overloading and downward movement; The significant deviation in estimating the weight of goods and the possibility of overloading and descending can lead to dangerous situations in elevators.