Patent Description:
Motion control for controlling the motions of motors used in machines and equipment may be performed using electronic cams. An electronic cam achieves the operation of a mechanical cam through electronic control and performs synchronization control for synchronizing a master axis and a slave axis to follow an electronic cam profile defined using software.

At an emergency stop of such an electronic cam system that performs synchronization control (hereafter, electronic cam control), a slave axis may stop at a position deviating from its intended position (hereafter, a position corresponding to the master axis) defined by a stop position of the master axis and the electronic cam profile. When resuming the electronic cam control with the slave axis deviating from the position corresponding to the master axis, the electronic cam system cannot operate each axis as intended. Techniques have been developed for calculating the position corresponding to the master axis using the position of the master axis after an emergency stop and for moving the slave axis to the calculated position corresponding to the master axis without moving the master axis (e.g., Patent Literature <NUM>).

Patent Literature <NUM>: <CIT>
<CIT> describes a position control device for controlling an axis of a machine in accordance with a command movement. The position control device obtains a command movement and calculates the position of the controlled axis and the position of a virtual axis. These positions are stored in a storage. The position control device then drives a controlled axis in a manner such that the controlled axis synchronously follows the virtual axis in accordance with the calculated positions. <CIT> describes a method and system of disengaging and engaging a servo axle group to be synchronized electronically with a master position value sequence. The method provides a synchronization of a speed and an angle of a servo group. The servo axles are driven by reference values, which are synchronized by master position values input into the axle group during engagement. The method further provides a synchronization of reference values of the servo axle group with master position values during disengagement based on a disengagement table of a correlation.

The slave axis can stop at the position deviating from the position corresponding to the master axis when the power to the controller is disconnected in, for example, a power outage or device maintenance. A known controller involves a manual operation of a worker to move the slave axis to the position corresponding to the master axis after the power disconnect.

One or more aspects of the present invention are directed to a controller that causes a slave axis to automatically return to a position corresponding to a master axis after a power disconnect.

In response to the above issue, a controller according to claim <NUM> is provided.

More specifically, a power disconnect in, for example, a power outage or device maintenance can cause the axes to be at reference positions different from the reference positions before the power disconnect. A known controller thus involves a manual operation of moving the slave axis to return to the position corresponding to the master axis after the power disconnect. The controller according to one or more aspects of the present invention recalculates the reference positions of the axes once power is restored. Thus, the controller causes the slave axis to automatically return to the position corresponding to the master axis after the power disconnect in, for example, a power outage or device maintenance.

The controller may further include an information provider that causes a state screen to appear on a display before the control is performed by the return control unit. The state screen may include a graph showing a relationship between the positions of the master axis and the slave axis and the electronic cam profile. The information provider may change the position of the slave axis shown in the graph in the return control in response to the return control being performed by the return control unit. The controller including the information provider allows a user to easily determine the situation. This controller increases user convenience.

The controller including the information provider may include the return control unit that starts the return control in response to a predetermined button on the state screen being operated.

The controller according to the present invention causes the slave axis to automatically return to the position corresponding to the master axis after a power disconnect in, for example, a power outage.

<FIG> is a diagram describing the configuration and implementation of a controller <NUM> according to one embodiment of the present invention.

The controller <NUM> according to the present embodiment is a programmable logic controller (PLC) developed for controlling a servo system <NUM>. The servo system <NUM> includes a master axis and multiple slave axes at positions controlled with reference to the position of the master axis.

The controller <NUM> may control any number of slave axis. The configuration and the functions of the controller <NUM> controlling the servo system <NUM> will be described below by way of example. The servo system <NUM> includes a motor 22a drivable by a servo driver 21a and a motor 22b drivable by a servo driver 21b as shown in <FIG>. The axis of the motor 22a is the master axis, and the axis of the motor 22b is the slave axis. Providing commands to control the position of the master axis (the axis of the motor 22a) and the position of the slave axis (the axis of the motor 22b) to the servo driver 21a or 21b may be hereafter simply referred to as controlling the positions of the master axis and the slave axis.

The controller <NUM> according to the present embodiment is a PLC connectable to an operation panel <NUM> and the servo system <NUM>. The controller <NUM> is programmed to be operable as a synchronization control unit <NUM>, a reference position storage <NUM>, a reference position updater <NUM>, a return control unit <NUM>, and a user interface (UI) control unit <NUM>. The operation panel <NUM> is a computer including a touchscreen, and functions as an input-output unit for the controller <NUM>.

The reference position storage <NUM> is a nonvolatile storage for storing the reference positions of the master axis and the slave axis. The reference position storage <NUM> also stores the positions of the master axis and the slave axis at the time when the master axis and the slave axis are synchronized with each other through cam control. These axis positions are hereafter referred to as the position of the master axis at cam synchronization and the position of the slave axis at cam synchronization. The controller <NUM> typically uses part of a rewritable nonvolatile memory such as a flash read-only memory (ROM), or storage such as a hard disk drive (HDD) that are included in the controller <NUM> as the reference position storage <NUM>.

The synchronization control unit <NUM> controls the position of the master axis (the rotation angle of the axis of the motor 22a). The synchronization control unit <NUM> also controls the position of the slave axis (the rotation angle of the axis of the motor 22b) to correspond to the position of the master axis to follow a preset electronic cam profile. The electronic cam profile used by the synchronization control unit <NUM> to control the slave axis includes information about the relationship between the phase of the master axis and the deviation of the slave axis shown in <FIG>. The phase of the master axis refers to a change in the position of the master axis either from its position at cam synchronization or from the reference position of the master axis. The deviation of the slave axis refers to a change in the position of the slave axis either from the position of the master axis at cam synchronization or from the reference position of the slave axis. For example, the information in the table shown in <FIG> can be used as the electronic cam profile. The data values (for phase and deviation) between the cam start point and the cam end point in <FIG> correspond to one cycle in <FIG>. The phase at the cam end point defined by the electronic cam profile is hereafter referred to as an end point phase, and the deviation at the same end point as an end point deviation. In the example in <FIG>, the end point phase is the phase of data at the cam end point, and the end point deviation is the deviation of data at the cam end point.

The reference position updater <NUM> performs a reference position update process every time the master axis reaches the cam end point during the cam control of the master axis and the slave axis performed by the synchronization control unit <NUM>. The reference position updater <NUM> also performs the reference position update process when the controller <NUM> resumes after a power disconnect in, for example, a power outage or device maintenance.

The reference position updater <NUM> performs the reference position update process by obtaining the position of the master axis from the servo system <NUM>, calculating the reference positions of the master axis and the slave axis based on the obtained master axis position, and updating the reference positions of the master axis and the slave axis stored in the reference position storage <NUM> using the calculation results. The reference position updater <NUM> calculates the reference positions of the master axis and the slave axis using Formulas (<NUM>) and (<NUM>) below. <MAT> <MAT>.

The current position of the master axis in Formulas (<NUM>) and (<NUM>) is the position of the master axis obtained from the servo system <NUM>. The floor refers to a floor function.

More specifically, as shown in <FIG>, when the position of the master axis at cam synchronization is <NUM>, the position of the slave axis at cam synchronization is <NUM>, the end point phase is <NUM>, the end point deviation is <NUM>, and the obtained current position of the master axis is <NUM>, the reference position of the master axis is calculated to be <NUM> and the reference position of the slave axis to be <NUM> by the calculations shown in the figure in the reference position update process.

The return control unit <NUM> (<FIG>) performs a return control process shown in <FIG>. The return control unit <NUM> performs the process after the controller <NUM> resumes and the reference position updater <NUM> completes the reference position update process after the power disconnect in, for example, a power outage or device maintenance.

Upon completion of the reference position update process by the reference position updater <NUM> after the power disconnect, the return control unit <NUM> starts the return control process by first reading the reference positions of the master axis and the slave axis from the reference position storage <NUM> (step S101). Subsequently, the return control unit <NUM> obtains the current position of the master axis from the servo system <NUM>, and calculates the current phase of the master axis by subtracting the reference position of the master axis from the obtained current position of the master axis (step S102).

The return control unit <NUM> then calculates, using the calculated current phase of the master axis and the electronic cam profile of the slave axis, the corresponding deviation of the slave axis, which is the deviation of the slave axis corresponding to the current position of the master axis (step S103). When the electronic cam profile is the information in the table in <FIG>, the return control unit <NUM> calculates the corresponding deviation of the slave axis, which is the deviation corresponding to the current phase of the master axis, using linear interpolation between the two deviation points at the two phases nearest the current phase of the master axis in the electronic cam profile in step S102, as in the example schematically shown in <FIG>.

After step S103, the return control unit <NUM> causes an operation screen to appear on the display of the operation panel <NUM> (step S103).

<FIG> is a diagram of an operation screen <NUM> appearing on the display of the operation panel <NUM> in step S103. As illustrated, the operation screen <NUM> includes an AUTO button <NUM>, an MPG button <NUM>, a RETURN button <NUM>, a graph area <NUM>, and parameter input fields <NUM> to <NUM>.

The graph area <NUM> includes a graph showing the relationship between the positions of the master axis and the slave axis (white circle) and the electronic cam profile (curve). The AUTO button <NUM> is to be pressed by a user for operation without specifying parameters, such as speed, used in controlling the position of the slave axis. The RETURN button <NUM> is to be pressed by the user for operation specifying parameters, such as speed, used in controlling the position of the slave axis. This button is to be pressed in response to intended values being entered in the parameter input fields <NUM> to <NUM>. The MPG button <NUM> is to be pressed by the user for manually controlling the position of the slave axis.

The return control unit <NUM> that has caused the operation screen <NUM> to appear on the display of the operation panel <NUM> waits for an instruction input by the user (step S103).

In response to the AUTO button <NUM> or the RETURN button <NUM> being pressed by the user, the return control unit <NUM> moves the slave axis to the corresponding position of the slave axis under the default conditions or the conditions specified by the user (step S104), and ends the return control process. In step S104, the return control unit <NUM> also changes the position of the white circle indicating the positions of the master axis and the slave axis in the graph on the operation screen <NUM> as the control proceeds.

In response to the MPG button <NUM> being pressed by the user, the return control unit <NUM> displays a control screen for manually controlling the position of the slave axis on the operation screen <NUM> in step S104. The return control unit <NUM> then controls the slave axis in accordance with the operation received on the control screen, and ends the return control process.

More specifically, in response to a power disconnect in, for example, a power outage or device maintenance, the axes can be at reference positions different from the reference positions before the power disconnect. A known controller thus involves a manual operation of moving the slave axis to return to the position corresponding to the master axis after the power disconnect. As described above, the controller <NUM> according to one or more embodiments recalculates the reference positions of the axes once power is restored after the power disconnect. Thus, the controller <NUM> causes the slave axis to automatically return to the position corresponding to the master axis without any inconvenience after the power disconnect.

The controller <NUM> described above may be modified variously. For example, the reference position updater <NUM> may perform the reference position update process at least once every cycle of control defined by the electronic cam profile. Thus, the reference position updater <NUM> may perform the reference position update process at a time different from the time described above (when the master axis reaches the cam end point). The reference position updater <NUM> may use any formulas other than Formula (<NUM>) or (<NUM>) described above to calculate the reference positions of these axes in the reference position update process.

Claim 1:
A controller (<NUM>) for performing synchronization control over a master axis and a slave axis to follow an electronic cam profile, the control device comprising:
a reference position storage (<NUM>) configure to store the reference position of the master axis and the slave axis, as well as the positions of the master axis and the slave axis at the time when the master axis and the slave axis are synchronized with each other through cam control;
a synchronization control unit (<NUM>) configured to control the position of the master axis and the position of the slave axis to correspond to the position of the master axis to follow the electronic cam profile;
a reference position updater (<NUM>) configured to, in response to power being restored after a power disconnect, obtain a position of the master axis and calculate a reference position of the master axis and a reference position of the slave axis based on the obtained position of the master axis, a position of the master axis at cam synchronization, and the electronic cam profile; and
a return control unit (<NUM>) configured to perform return control to determine a position of the slave axis corresponding to a current position of the master axis based on the current position of the master axis, the electronic cam profile, and the reference position of the master axis and the reference position of the slave axis calculated by the reference position updater (<NUM>), and to move the slave axis to the determined position,
wherein the electronic cam profile presents information indicating the relationship between the phase of the main axis and the displacement amount of the slave axis, wherein the phase of the master axis refers to a change in the position of the mater axis either from its position at cam synchronization or from the reference position of the master axis, and the deviation of the slave axis refers to a change in the position of the slave axis either from the position of the master axis at cam synchronization or from the reference position of the slave axis.