A multi-axis servo control system includes a plurality of motors and a plurality of drive control apparatuses. The drive control apparatuses are connected to each other through an external field bus. Each drive control apparatus includes a control unit and a plurality of drive units. The drive units are connected to the control unit in series by a plurality of local buses to form a series-connected communication loop of sequentially transmitting data. Each drive unit controls at least one of the motors. The control unit receives multi-axis position commands through the external field bus, and the drive units correspondingly receive multi-axis commands through the local buses so as to control the motors in a decentralization manner.

A protective redundancy circuit is provided for a power tool having an electric motor. The protective redundant subsystem is comprised of: a motor switch coupled in series with the motor; a motor control module that controls the switching operation of the motor switch; and a protective control module that monitors switching operation of the motor switch and disables the power tool when the switching operation of the motor switch fails. In the context of an AC powered tool, the switching operation of the motor switch is correlated to and synchronized to the waveform of the AC input signal. During each cycle or half cycle, the motor control module introduces a delay period before closing the motor switch and the protective control module determines the operational status of the motor switch by measuring the voltage across the motor switch during the delay period.

A speed control system of a universal motor is electrically connected with a universal motor and includes a speed detecting unit and a controller. The controller is provided with a slow start unit, a speed control unit and a stopping-protecting unit. The slow start unit enables the rotating speed of the universal motor to increase smoothly, and the speed control unit controls and compensates the rotating speed of the universal motor in a way of closed loop, able to achieve effect of stepless speed adjustment and, when used at low speed, having cutting ability similar to that when operated at high speed. The stopping-protecting unit is able to automatically cut off power and carry out protection when machine table is stopped.

In a current sensor abnormality diagnosis device, an abnormality judgment section determines that the phase current sensors are operating normally when a sum of three phase currents is not more than a threshold value, and a bus current sensor is operating normally based on a comparison result between three phase currents and a bus current. The abnormality judgment section detects which the phase current sensor has failed based on the three phase currents and the bus current when the sum of the three phase currents is more than the threshold value. Because of using the comparison results of the three phase currents with the bus current in addition to the sum of the three phase currents, it is possible for the abnormality judgment section to detect the occurrence of abnormality of each of these current sensors even if the detected current has an undefined value.

In a current sensor abnormality diagnosis device, an abnormality judgment section determines that the phase current sensors are operating normally when a sum of three phase currents is not more than a threshold value, and a bus current sensor is operating normally based on a comparison result between three phase currents and a bus current. The abnormality judgment section detects which the phase current sensor has failed based on the three phase currents and the bus current when the sum of the three phase currents is more than the threshold value. Because of using the comparison results of the three phase currents with the bus current in addition to the sum of the three phase currents, it is possible for the abnormality judgment section to detect the occurrence of abnormality of each of these current sensors even if the detected current has an undefined value.

A multi-axis servo control system includes a plurality of motors and a plurality of drive control apparatuses. The drive control apparatuses are connected to each other through an external field bus. Each drive control apparatus includes a control unit and a plurality of drive units. The drive units are connected to the control unit in series by a plurality of local buses to form a series-connected communication loop of sequentially transmitting data. Each drive unit controls at least one of the motors. The control unit receives multi-axis position commands through the external field bus, and the drive units correspondingly receive multi-axis commands through the local buses so as to control the motors in a decentralization manner.

The subject matter of this specification can be embodied in, among other things, a system that includes a flexible structure, a power inverter, a first electromechanical device configured to urge movement of a first portion of the flexible structure based on power received from the power inverter, a second electromechanical device configured to urge movement of a second portion of the flexible structure based on power received from the power inverter, a feedback sensor configured to provide a feedback signal indicative of alignment between the first portion and the second portion, and a controller configured to control operation of at least one of the first electromechanical device and the second electromechanical device based on the feedback signal.