HOFMANN motor Germany HOFMANN model HOFMANN price

HOFMANN motors are a type of electric motor powered by simultaneously connecting to 380V three-phase AC current (with a phase difference of 120 degrees). Because the rotor of a three-phase asynchronous motor rotates in the same direction but at a different speed than the stator's rotating magnetic field, there is slip, hence the name three-phase asynchronous motor. The rotor speed of a three-phase asynchronous motor is lower than the speed of the rotating magnetic field. The rotor windings generate electromotive force and current due to relative motion with the magnetic field, interacting with the magnetic field to produce electromagnetic torque, achieving energy conversion.

HOFMANN motor performance

Common lubrication methods for motor spindle bearings include grease lubrication, oil mist lubrication, oil-air lubrication, jet lubrication, and under-ring lubrication. Grease lubrication requires no additional equipment and is widely used for low-speed spindles. Oil mist lubrication atomizes lubricating oil (such as turbine oil) using compressed air to lubricate the bearings. This method is easy to implement and uses simple equipment; the oil mist provides both lubrication and cooling. However, oil mist is difficult to recover and causes significant environmental pollution, so it is gradually being replaced by the newer oil-air lubrication method. Oil-air lubrication delivers small amounts of lubricating oil directly to the bearing lubrication zone along dedicated oil-air pipes using compressed air at regular intervals and quantities, without atomization. The lubricating oil provides lubrication, while the compressed air drives the oil movement and cools the bearings. The oil and air remain separated, which facilitates oil recovery and avoids environmental pollution. When implementing oil-air lubrication, each bearing generally requires a separate oil-air nozzle, with strict requirements for the injection position to ensure effective lubrication. The effectiveness of oil-air lubrication is also influenced by compressed air flow and oil-air pressure. Generally, increasing air flow improves cooling, while increasing oil-air pressure not only improves cooling but also helps the lubricating oil reach the lubrication zone, thereby helping to increase bearing speed. Experiments show that increasing pressure can increase bearing speed by 20% compared to conventional pressure oil-air lubrication. Jet lubrication directly uses high-pressure lubricating oil to lubricate and cool the bearings, resulting in high power consumption and cost.

HOFMANN motor operating mode

Motor starting methods: Soft start. With the rapid development of microcomputer control technology, a series of electronic soft-start controllers have been successfully developed in relevant control engineering fields and are widely used in motor starting processes, replacing reduced-voltage starters. Current electronic soft-start facilities use thyristor voltage regulation circuits, configured as follows: six thyristors, connected in anti-parallel pairs and then in series to the three-phase power supply. Upon receiving a start signal from the system, the microcomputer-controlled starter immediately performs data calculations and sends trigger signals to the thyristors. This controls the conduction angle of the thyristors, adjusting the output voltage according to the given output to achieve motor control. This starting method is suitable for starting control of three-phase AC asynchronous motors of various power ratings, including six-wire and three-wire connection configurations. Direct start. This is the most basic and simplest motor starting method. First, a knife switch is used to connect the motor to the grid. The motor starts and runs at rated voltage. Characteristics of this method include low investment, simple equipment, and few components. Although the starting time is short, the starting torque is low and the current is high, making it more suitable for starting low-capacity motors. Reduced-voltage start. Due to the significant disadvantages of direct starting, reduced-voltage starting was developed. This method is suitable for no-load and light-load conditions. Since reduced-voltage starting limits both starting torque and starting current, the circuit must be restored to its rated state after the starting process is complete.

HOFMANN motor control principle

When the motor rotates, the control unit compares the speed composed of the speed and acceleration/deceleration rates set by the driver with the speed of hall-sensor signal changes (or via software calculation) to determine which next set of switches (AH, BL or AH, CL or BH, CL or ...) conducts, as well as the conduction duration. If the speed is insufficient, the conduction time is lengthened; if the speed is excessive, it is shortened. This part of the work is completed by PWM. PWM determines whether the motor speed is fast or slow; how to generate such PWM is core to achieving precise speed control. High-speed control must consider whether the system's CLOCK resolution is sufficient to handle the processing time of software instructions. Additionally, the data access method for hall-sensor signal changes affects processor performance, judgment accuracy, and real-time capability. For low-speed control, especially low-speed starting, the returned hall-sensor signal changes more slowly. Therefore, the signal acquisition method, processing timing, and appropriate configuration of control parameters based on motor characteristics become very important. Alternatively, speed feedback can reference encoder changes to increase signal resolution for better control. Smooth motor operation and good response cannot ignore the appropriateness of P.I.D control. As previously mentioned, brushless DC motors use closed-loop control, so the feedback signal indicates to the control unit how much the motor speed deviates from the target speed, which is the error.

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