Electro-Permanent Magnetic Lifters: Failsafe and Variable Holding Power

Electro-permanent magnetic lifters counter the limitations of permanent and electromagnets by combining the advantages of both.

The restricted lifting capacity of permanent magnetic lifters and the non-failsafe operation of electromagnetic lifters are two limitations of these types of lifters. To overcome these limitations, lifting magnet designers have created the electro-permanent magnetic lifter, which combines the advantages of both the permanent and electromagnetic lifters in one module.

Types of Magnets

There are three types of magnetic lifter technologies: permanent magnetic, electro-magnetic and electro-permanent magnets. The permanent lifting magnets use failsafe, permanent magnets, but they do not have a variable holding power capability, which restricts both their load capacities and the variety of applications they are best suited for.

Electro-magnetic lifters use a controller to generate a DC voltage in a coil embedded within the lifter module to generate the magnetic work holding force. The DC controller’s voltage can be adjusted to vary the magnetic flux field, which, in turn, varies the holding force of the electromagnetic lifter. This feature makes electromagnetic lifters flexible holding devices and very cost-effective as well. But electromagnetic lifters require continuous electrical power to operate. A power failure will de-energize the electromagnet, shut down the magnetic field, and create a potential safety hazard. Electro-permanent magnetic lifters counter these limitations.

Electro-permanent Lifter Operation

Electro-permanent magnetic lifters (commonly called electroperms) are a hybrid of the permanent and electromagnetic types. They are constructed with a coil wound around a magnetic material that is permanent, embedded in the lifter module. When a DC voltage is applied, the material is charged, which takes about 1 second, and attracts the material to the lifter even after power is removed. The lifter will hold the load until the electro-permanent magnet is turned off. This features gives electro-perms a failsafe operation.

Another function of the electroperm’s coil is to control the amount of magnetic force of the lifter. This feature gives it a variable holding power capability similar to electromagnetic lifters. This feature extends the types of applications the electroperm is suited for. Electroperms can be used in tandem for beam lifting operations as well as for light load, pick and place, robotic operations. For pick and place operations, the electroperm is modified to be lightweight for maximizing end-of-arm capacity. They are constructed with special coil configurations for fast switching with minimum dwell times and soft pole shoes contoured to provide the easiest access to the part.

Battery Operation

Electro-permanent magnetic lifters are sometimes called battery lifters because a battery instead of a D.C. controller is used to provide the power for the electroperm switching cycle. The battery gives the lifter portability. It also makes for a simpler system design because a complex D.C. controller is not necessary. However, the battery will require maintenance and periodic charging.