Vibration motors can be controlled by varying the applied voltage, this is how haptic devices create different vibration patterns. Increase the voltage, and the motor turns faster thereby increasing the vibration strength and the vibration frequency. Reverse the polarity and the motor is forced to turn in the opposite direction, commonly used to stop it quickly.
To help customers understand the performance, our datasheets show how each motor performs over a range of voltages. However, if you explore further into the datasheet you will find we actually include 4 different voltages to profile our products.
We’ll take the 306-101 as an example to explain each in turn, and why they’re important.
Typical Start Voltage
The key word here is typical. This is the voltage at which the motor will normally start to vibrate. Due to manufacturing tolerances, there are slight variations in the behaviour of each motor – even those from the same batch.
The Typical Start Voltage is an average value calculated from our in-house testing. It matches with the start of the Typical Performance Characteristics graph and is the minimum voltage you can expect to start the motor turning.
However, as the motor requires a little extra help to overcome the inertia of the eccentric mass the Typical Start Voltage is actually a little higher than the minimum voltage. In other words, if the motor is already running it can continue to operate at voltages below the Typical Start Voltage.
Certified Start Voltage
This is part of the motor’s specification, and the voltage where the motor is guaranteed to start working. Although the motor would typically start before this voltage – it is not considered defective if it operates here.
This would not normally show on the performance graph as the Certified Start Voltage is always above the Typical Start Voltage (otherwise the motor’s would be typically defective!)
This is where the motor is designed to operate. Almost all other specifications and characteristics are taken at the Rated Voltage. The vibration system is almost always designed to operate at or around this value, although haptic feedback products are almost constantly varying the applied voltage.
Note that a higher Rated Voltage does not necessarily mean a stronger motor there are influences from other factors in the internal construction and other design aspects.
Maximum Operating Voltage
This is the highest voltage you can apply to the motor – the further above it the higher the risk of causing the motor to fail. Even operating at this voltage can reduce the lifetime of the motor due to the increased mechanical wear from the increase speed and operating temperature.
However, it is very common for haptic feedback designs to power the motor at the maximum operating voltage. The advanced technique of ‘overdrive’, a feature found in many haptic drivers, involves applying the Maximum Operating Voltage to the motor for a short period. This rapidly increases the vibration strength to produce a lower start time, and crisper haptic experience for the user. In this instance, the motor life is not effected as the driver reduces the applied voltage as the actuator gets up to speed.