Improve Haptic Motor Power-efficiency
05/11/2022 Emily Zhang

Haptic Technology creates a tactile sensation when humans communicate or interact with electronic, automotive and industrial devices by means of force, resistance, rotation or vibration. Haptic technology has made remarkable breakthroughs since Immersion Corporation began licensing of haptic technology in 2010. Developers and haptics users have been mutually innovating more solutions to enhance interactive haptic effects and improve feedback systems. However, higher energy consumption is becoming a gating factor in haptic technology. Most devices incorporating haptics, such as tablets, smartphones, laptops, and wearables use a limited battery-based power source and haptics applications are one of the more power intensive systems in most electronics.

Consuming high energy is a major issue slowing haptic technology expansion. As one of the most critical components of the haptics system, haptic motors consume a large quantity of energy. Many innovations to the motor design, components and constructure are necessary to minimize the energy consumption while retaining or improving the haptic feedback effects.

Higher power-efficiency is a solution where the motor is designed to output more power while retaining the same motor volume. That means the motor construction must be re-created. For instance, game controller motors, an ERM driven by DC current, has a typical rotor/stator matching, i.e. a pair of magnets (2-pole) in the stator, reacting with a rotor which has 3-slot iron laminations and 3-sector commutator. If we increase to 2 pairs of magnets into the stator (4-pole), and stack 6-slot iron laminations and 6-sector communicator, it is possible the same volume is equivalent running 2 typical motors at the same time, and it would be capable of maximizing the output power within limited body. A Current controller trigger motor, diameter 12mm and 12mm length, has 2-pole stator and 3-slot rotor constructure, it can output 1.0g-cm torque at the rated loading rotation. If in the same shell, a 4-pole stator and 6-slot rotor constructure is introduced, such 12x12mm cyclinder will be generating 3.9g-cm torque at maximum efficiency point, indicating a 290% increase. The users are projected to detect stronger interactive feedback and more immersive gaming experiences. The feedback quality is absolutely improved, also more haptic complexity is added combining with the multiple-pattern haptic driver.

ERM is a rotation (as opposed to linear) type motor, whose rotor consists of coil windings on an iron core with slots/openings. Usually, the iron laminations are vertically straight, but if the rivet fixture is modified, so as to rivet out the chute-slot laminations, the outline of the lamination looks twisted at a certain angle, and the coil winding has an offset compared to the regular. That will change the intersection angle between the brush and the commutator, which is welded/soldered with the coil, during phase altering. The chute-slot rotor contributes to the forward phase switch, requiring lower stalling voltage as an energy saving solution, such chute-slot morot is benefical for shortening the starting time as well.

In considering potential variable changes, it is possible to get lower current at the same voltage by changing to a smaller coil wire diameter or adding more turns in the winding, but this is on the baisis that the motor performance is allowed to be changed. If the application requires a certain performance or output power, in order to cut the energy consumption, we may need to re-arrange the coil winding and re-design the filling rate of the coil winding in each slot. In addition, we need to care for other concerns related to potential copper coil loss. The multi-layer coil distribution needs to be taken into the account.

Iron loss is a major efficiency concern, we propose to think about three major elements to lower the iron loss, including quality iron material with lower iron loss, optimizing the iron structure/shape and properly design the slot/opening for the coil winding. All three potential optimizations can be investigated in FEA simulation. It is highly recommended to do a component material study before designing the motor combining the motors expected use and application constraints.

EMC (electromagnetic compatibility) supression performance is also a useful pathway to reduce the energy consumption and sustain motor life longevity. The varistor can be placed very close to the commutator circuit to protect against the back electromotive force to reduce the inrush spike voltage, a small ceramic capacitor will do the job as well if necessary. Another simple EMC solution is PCB ring, capacitor charge-discharge based, which is beneficial to balance and protect the circuit for EMC purpose.

For other tips about lowering the energy consumption of haptic motors, we may need to discuss the horizontal stray field induced by the tororidal field coils and primary windings, controlling the interplace between rotor and magnetic tiles, and internal mechanical friction consumption. All the considerations aim to save energy in haptics enabled devices, especially those battery-based, from the component material identificaiton, semi-assembly design to manufacturing details. A series of factors must be significantly evaluated to unlock a pathway to make the best use of a haptic motor.

To learn more about Quadrant's haptic technology, contact us here.