All electric motors operate with inherent losses from a number of different areas. Some are inherently mechanical (think friction losses as heat) while others are electrical, from current in conductors, also known as I²R losses, to losses due to hysteresis and eddy currents in the iron components of a motor.

One type of loss that is especially pernicious is leakage current from the motor to ground. The fact is that some small amount of current can flow from the motor to ground in all electrical equipment, usually as a result of some type of fault in the equipment or cabling. The amount for the most part is small, perhaps on the order of milliamps, but it is present nonetheless and poses a safety risk to human operators.

Several sources of leakage current are shown here including from the motor itself as well as from the motor cable. (Image via TDK)

Leakage currents can flow through the insulation surrounding conductors. Electrically speaking, insulators have both resistance and capacitance, and leakage current can flow through both. Old or damaged insulation means a lower resistance and hence more potential current flow. Also, the longer the conductor the more capacitance, and therefore more leakage current flow. Typical allowable leakage currents in IT and medical equipment, for instance, are in the range of a milliamp or two to sub-milliamps.

So what is likely to cause leakage currents? For one, unshielded cables. Also, any other sources of electrical noise that can couple to the motor or motor cabling. Remember, leakage current can be an indicator of trouble in conductors and insulators. A common way to check for leakage current is to use a clamp-type current meter that fits around a conductor and gives a read-out of the current. The best ways to prevent leakage current are to always use shielded cables on motor installations and to make sure that these cables are grounded at both ends. Also, check cables and insulation for damage and replace ones that are broken or damaged.

Integration in motion control is commonplace. Integrated servocontrols can refer to both the way in which the integration of the controller into a servo system (or motor) takes place as well as the control options and functions integrated into the controls themselves.

By integrated here we mean that the controller is integrated into the motor. This is a fairly common practice these days and in fact most manufacturers offer servomotors with some level of built-in controls. Such systems are often dubbed integrated servomotors. As for what exactly is integrated, there can be a range of components so that an integrated servomotor can include the motor itself along with any combination of a drive, controller, or encoder.

The benefits of integration are well known. They include the fact that they make for a more compact drive unit and eliminate the need for cables between the motor and drive, which simplifies installation and also lowers the overall system cost. The tight integration of controls with the motor and other components makes for a compact design, with the ability to fit into smaller spaces but also pack more into that same space than before. Another benefit of these systems is the elimination of control cabinets, with the control itself being distributed and local at the servomotor itself.

These ACSI EtherNet/IP integrated servos from Tolomatic feature a servomotor integrated with a drive and controller.

The kinds of options can mean which functions are included in the controls. For example, this includes basics like the number of inputs and outputs as well as signal types (analog or digital.) Other common options may include the type of control, such as current of speed control.

Other options can include specific control functions such as PID loop control, trajectory generation, program execution, I/O control and communication options such as whether the servocontroller operates as a stand-alone controller or connected into a network with other controllers.