The current collector is one of the most important components
in the sliding contact line system.
The current collector is the main device for picking up electrical energy on the current collection side in the sliding contact line system. It directly conducts electrical energy to the electrical appliance through the sliding contact between the carbon brush and the guide rail, thereby achieving mobile power supply for the system. The current collector consists of two parts: a mechanical tension device and a carbon brush that directly slides in contact with the guide rail.
The mechanical tension device determines the sliding contact pressure between the carbon brush and the guide rail and the stability of the mechanism. The carbon brush is the conductor that slides in contact with the guide rail to pick up electrical energy. Its performance, conductive quality, and the quality of its material composition will directly affect the safe operation quality of the entire system equipment.
There are many types of current collectors, and those commonly used in testing include: pull-wire type, brush type, and inductive type. The first two are contact-type current collectors, while the latter is a non-contact type.
Pull-wire type current collector
The structural principle of the pull-wire type current collector is shown in the figure on the right.
Pull-wire type current collector
On the circular shaft 1, a bakelite inner ring 2 is fixed, and on its groove, a collector ring 3 is embedded, which is connected to the strain gauge attached to the shaft. In this way, electrical signals are transmitted from the collector ring 3, through the pull wire 4, insulating plate 5, and terminal 6, to the measuring instrument. The pull wire 4 is tensioned by a spring 7 to ensure good contact with the collector ring.
This type of current collector is suitable for situations with relatively low linear speed (≤4 m/s) and short operation time. Its advantages are simple structure, low process requirements, and reliable contact, but it has high wear and low lifespan.
Brush type current collector
Brush type current collectors can be divided into radial brush type and end-face brush type. Radial brush type
Brush type current collector
In the radial brush type, the circumferential surface of the collector ring contacts the brush, while in the end-face brush type, the side surface of the collector ring contacts the brush. The structural principle is shown in the figure on the right. The inner ring 1 of the current collector is fixed on the rotating shaft being measured, and it has three (for half-bridge measurement) or four (for full-bridge measurement) collector rings 3, which are insulated from each other and from the inner ring, and are connected by wires to the strain gauges attached to the shaft. On the housing, mutually insulated brushes 2 are fixed, and springs 4 press the brushes against the collector rings. Each brush has a lead wire. In this way, the electrical signals on the rotating shaft are transmitted to the measuring instrument through the contact between the collector rings and the brushes.
The radial brush type current collector has a simple structure and is easy to use, but the contact resistance is not very stable, so it is only suitable for low speed and low precision requirements. The end-face brush type current collector relies on side contact, and the contact resistance is relatively stable, making it suitable for higher speed and high precision requirements.
When designing a current collector, the following points should be noted:
① The materials of the collector ring and brush should be selected appropriately to ensure low contact resistance and low friction coefficient. For general current collectors, the collector ring can be made of red copper, and the brush can be made of graphite-copper alloy. For current collectors with high measurement precision, the collector ring is best made of pure silver or Monel alloy, and the brush is best made of graphite-silver alloy.
② The number of brushes on each collector ring affects the magnitude and stability of contact resistance. Too few brushes make operation unreliable, while too many complicate the structure. Generally, it is appropriate to arrange 2 to 4 brushes symmetrically.
③ The contact pressure between the brush and the collector ring also affects the magnitude and stability of contact resistance. If the pressure is too low, the contact resistance is large and unstable; if too high, it causes wear and heat, reducing lifespan. Generally, the pressure should be between 60 and 80
.
④ The pressure springs for each brush on the same collector ring should preferably have different natural frequencies to ensure that during strong vibration, the brushes do not bounce up simultaneously and maintain good contact.
Inductive type current collector
The inductive type current collector is also called a rotary transformer type or non-contact type current collector. Its working principle is to use electromagnetic induction to transmit the measurement electrical signals from the rotating part to the fixed part, eliminating various contact points, so there are no problems such as contact resistance.
Inductive type current collector
