Technical Note:
Picomotor Motion Definitions of Characteristics

99-PICOSTEP
Average Picomotor actuator step size vs. load. This data was taken using an interferometer as the Picomotor actuator lifted loads ranging from 1 to 6 lbs.

Angular Resolution

The smallest rotation you can make with the Picomotor™ actuator. This is the typical rotation caused by applying a single voltage pulse to the Picomotor actuator. Since the Picomotor actuator relies on friction to turn the screw (it’s a stick–slip actuator), the actual angle change per pulse varies a small amount with the direction of rotation, load, temperature, and wear of the unit. We typically observe variations of a few percent (or less) in angle change per pulse, while moving in one direction at a constant load and temperature.

Angular Travel

The maximum total change in the angle of the mounting plate relative to the base in our motorized stages.

Degrees of Freedom

The total number of translation directions plus rotation directions that you can change by rotating the adjustment screws on our mounts and stages (whether motorized or not).

Flip-to-Flip Repeatability

The difference in angular position between consecutive flips.

Holding Force

The amount of force exerted by the motors to keep the position of the stage.

Lifetime

The total number of hours that the motor can be continuously operated at the indicated pulse repetition rate.
For the Picomotor actuators there is a linear relationship between lifetime and pulse repetition rate; running the motors at a slower rate will result in a proportionally longer life.

Linear Travel

The maximum possible Picomotor actuator translation. This is limited only by the length of the Picomotor actuator’s screw.

Maximum Load

For the Picomotor actuator, the maximum weight the stage can handle. The force that the Picomotor actuator or stage (or Picomotor actuator-equipped mount or stage) can exert before stalling. Since the Picomotor actuator and closed-loop stages depend on friction to move, large loads can prevent the actuator from moving at all. As the maximum load on a Picomotor actuator is approached, the typical step size is decreased. (See graph below.) For closed-loop stages, the maximum load is the load the stage can hold and still move.

Minimum Incremental Motion

The smallest translation you can make.

Motorized Axes

Of the possible degrees of freedom of the mount or stage, the number that are motorized.

Operating Temperature

Our specifications are guaranteed only in this temperature range. If your application demands high- or low-temperature operation, call us for more information.

Speed

For linear positioners, this is the Picomotor actuator’s translation rate with no load; for the rotary, it is the rotation rate. The speed of the device is directly related to the rate at which pulses are applied, the minimum angular resolution, and, in the case of linear positioners, the screw thread pitch. We calculated speed assuming a pulse rate of 1 kHz, which all our drivers can produce.

Step Size

The typical translation caused by applying a single voltage pulse to the Picomotor actuator. Since the Picomotor actuator relies on friction to turn a screw, the step size will vary slightly from pulse to pulse. (See “Angular Resolution” for more information.)

Torque

The torque that the Picomotor actuator can exert before stalling. Since the Picomotor actuator depends on friction to move, overloads can prevent the actuator from moving at all. As maximum torque load is approached, typical step size decreases.

Total Repeatability

The difference in angular position between the first flip and the 10,000th flip.

Typical Accuracy

A measure of the degree to which a given displacement matches a standard.

Typical Bi-Directional Repeatability

A measure of how well the device returns to a set position over many attempts and when approached from either direction.