Numerical control system

In a numerical control system in which a numerical controller is connected with a plurality of amplifiers via a daisy-chain serial bus, these amplifiers are grouped into a first group and a second group, and connected in an order of the amplifiers of the first group and the amplifiers of the second group from the numerical controller. Further, a communication cycle in the communication between the numerical controller and the amplifiers of the second group is set n times (n is an integer of 2 or larger) as large as a communication cycle of the first group.

RELATED APPLICATION DATA

This application claims priority under 35 U.S.C. §119 and/or §365 to Japanese Application No. 2013-267115 filed Dec. 25, 2013, the entire contents is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a numerical control system capable of appropriately controlling communication with communication devices and efficiently using a communication band.

2. Description of the Related Art

FIG. 6is a block diagram illustrating a numerical control system according to a related art.FIG. 7is a block diagram illustrating an example of transmission from a numerical controller to amplifiers in the numerical control system according to the related art. As illustrated inFIG. 7, in the numerical control system according to the related art, in communication from the numerical controller10to an amplifier, a numerical controller10transmits transmission data to all amplifiers in each communication cycle. Further, as illustrated inFIG. 8, in the numerical control system according to the related art, in communication from the amplifier to the numerical controller10, all the amplifiers transmit transmission data to the numerical controller in each communication cycle.

In an industrial network, it is important to guarantee that communication is necessarily executed (punctuality) within a certain communication period of time. As the punctuality is guaranteed, a network can be applied to an application in which a strict real time property such as synchronous control of motion control is required. In a numerical control system in which the punctuality is guaranteed, a communication period of time, a communication cycle, the number of communication devices, a communication data amount, a distance between communication devices, and the like are specifically decided and managed.

For example, IEEE1394 serving as an international standard is not an industrial communication standard, but isochronous transfer is specified as a method of guaranteeing punctuality of real-time data in which it is problematic if a reproduction operation stops in the middle of reproduction such as an image or a sound (see Japanese Patent Application Laid-Open No. 2002-319942). Specifically, a transfer band is divided into isochronous transfer and non-isochronous transfer in a time division manner, and a decided amount of data is transferred to a decided number of devices during a period of time allocated to the isochronous transfer.

In the related art, in communication in which punctuality is guaranteed, since a communication period of time, a communication cycle, the number of communication devices, a communication data amount, a distance between communication devices, and the like are specifically decided and managed, there is no flexibility in a communication system. As described above, in the communication scheme of the related art, the punctuality is secured in communication between the numerical controller and the amplifier, but since communication cycles are uniformly decided, even when there is an amplifier that can be controlled even in a slow communication cycle, it is necessary to adjust a communication specification according to an amplifier that desires a fastest communication cycle. As a result, the number of connectable amplifiers is limited, and if it is simply assumed that the numerical controller performs direct communication with the amplifiers via a serial bus in a one-on-one manner, and there is neither delay in a communication path nor circuit delay caused as a communication packet passes through each amplifier, the following inequality holds:
T×R>N×B

Here, T (s) indicates a communication cycle,

R (bps) indicates an effective communication rate,

N indicates the number of amplifiers, and

B (bit) indicates a communication amount per amplifier.

Further, transmission and reception data amount of serial communication is equal to transmission and reception data amount of all amplifiers.

In a system in which a communication rate of serial communication and a communication amount per amplifier are already decided, a communication cycle is in inverse proportion to the number of connectable amplifiers.

As described above, when there is an amplifier that desires a fast communication cycle and a serial communication cycle is made fast according to the amplifier, the number of connectable amplifiers is reduced.

SUMMARY OF THE INVENTION

In this regard, in light of the problems of the related art, it is an object of the present invention to provide a numerical control system which is capable of appropriately controlling communication with communication devices and efficiently using a communication band since there are many communication devices that desire punctuality but have a lax communication purpose, for example, do not care about a lengthy communication cycle or a small communication data amount.

In a numerical control system according to a first aspect of the present invention, a numerical controller and a plurality of units are connected via a daisy-chain serial bus, and transmission from the numerical controller to the plurality of units is performed via the serial bus and transmission from the plurality of units to the numerical controller is performed via the serial bus. The plurality of units are grouped into a first group and a second group, and are connected in an order of the units of the first group and the units of the second group from the numerical controller. And a communication cycle in the communication between the numerical controller and the units of the second group is set n times (n is an integer of 2 or larger) as large as a communication cycle in the communication between the numerical controller and the units of the first group.

Among the units of the second group, a certain number of units close to the numerical controller may be classified into a second group first subgroup and the remaining units may be classified into a second group second subgroup, and the units of the second group first subgroup may receive and store signals transmitted from the units of the second group second subgroup toward the numerical controller, and may select the stored signals or signals of the units of the second group first subgroup, and may transmit the selected signals to the numerical controller in each communication cycle of the first group.

The units may be amplifiers each driving and controlling a motor or an IO unit that transfers a DI/DO signal.

In a numerical control system according to a second aspect of the present invention, a numerical controller and a plurality of amplifiers are connected via a daisy-chain serial bus, each of the plurality of amplifiers drives a motor based on a command of a certain cycle transmitted from the numerical controller via the serial bus, and feedback data on the command is transmitted to the numerical controller via the serial bus. The plurality of amplifiers are grouped into a first group and a second group, and are connected in an order of the amplifiers of the first group and the amplifiers of the second group from the numerical controller. And a communication cycle in the communication between the numerical controller and the units of the second group is set n times (n is an integer of 2 or larger) as large as a communication cycle in the communication between the numerical controller and the units of the first group.

Among the amplifiers of the second group, a certain number of amplifiers close to the numerical controller may be classified into a second group first subgroup, and the remaining amplifiers may be classified into a second group second subgroup, and the amplifiers of the second group first subgroup may receive and store feedback data transmitted from the amplifiers of the second group second subgroup toward the numerical controller, and may select the stored feedback data or feedback data of the amplifiers of the second group first subgroup, and may transmit the selected feedback data to the numerical controller in each communication cycle of the first group.

According to the present invention, in a numerical control system in which punctuality is guaranteed, communication with a machine to which a long communication cycle is allowable is carried out in a cycle that is n times as large as a typical cycle (n is an integer of 2 or larger). Thus, it is possible to provide a numerical control system capable of increasing the number of communication devices and a total line length of a communication line without influencing communication with other communication devices.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1is a block diagram illustrating a numerical control system according to a first embodiment of the present invention.

The numerical controller10transmits a command value of a position, a speed, torque, or an electric current to each amplifier that drives and controls each motor equipped in a machine body, and receives feedback on a position, a speed, torque, or an electric current from each amplifier. InFIG. 1, a “command value” indicates a command value of a position, a speed, torque, or an electric current, and “feedback” indicates feedback on a position, a speed, torque, or an electric current.

In the numerical control system ofFIG. 1, an amplifier group A includes j amplifiers1to j, an amplifier group B includes k amplifiers1to k, and the numerical controller10is connected with the amplifier group A including the j amplifiers and the amplifier group B including the k amplifiers via a daisy-chain serial bus in the order illustrated inFIG. 1. A communication cycle Tb in which transmission and reception are performed between the numerical controller10and the amplifier group B is n times (n is an integer of 2 or larger) as large as a communication cycle Ta in which transmission and reception are performed between the numerical controller10and the amplifier group A.

In other words, a command is transmitted from the numerical controller10to the amplifiers through data transmission of the cycle Ta to the amplifier group A and data transmission of the cycle Tb (=Ta×n) to the amplifier group B. Meanwhile, similarly, feedback is transmitted from the amplifiers to the numerical controller10through data transmission of the cycle Ta from the amplifier group A and data transmission of the cycle Tb (=Ta×n) from the amplifier group B. At this time, among the amplifiers included in the amplifier group B, one or more amplifiers included in a cluster of m amplifiers (an amplifier subgroup B1including m amplifiers, that is, amplifiers1to m) closest to the numerical controller10in the daisy-chain is configured to store transmission data transmitted from the amplifiers (an amplifier subgroup B2including amplifiers (m+1) to k) at the subsequent stage and transmit the stored transmission data together with transmission data of their own in the cycle Ta. Here, m is assumed to be larger than k÷2 (m>k÷2).

The amplifier subgroup B1performs transmission and reception with the numerical controller10on the communication line in the same cycle (Ta) as the group A, and from a point of view of a communication capability, the amplifiers of the group A and the group B1can be connected to this communication line up to a limit of the number of amplifiers that allows to perform transmission and reception in the cycle Ta. In addition, the (k−m) amplifiers excluding the group B1among the amplifier group B, amplifier subgroup B2, are connected to this communication line, and it is possible to increase the number of amplifiers that can be connected to the communication line without completely changing the communication specification of the amplifiers group A.

FIG. 2is a block diagram illustrating a numerical control system according to a second embodiment of the present invention.

In the numerical control system according to this embodiment, a communication cycle of one of N amplifiers is set to be double, and one amplifier is newly added. In other words, a total line length of a system is increased such that a communication cycle of one (an amplifier N) of predetermined N connectable amplifies (amplifiers1to N) is set to be double, and another amplifier (an amplifier (N+1) having the same communication cycle (double the communication cycle) as the amplifier N is connectable. Since the communication band of the amplifier N of the related art is shared between the amplifier N and added another amplifier N+1, there is no influence on the amplifiers (the amplifiers1to N−1) other than the amplifier N.

FIG. 3is a diagram illustrating an example of transmission from the numerical controller10to the amplifiers in the numerical control system according to the present invention.

In the example ofFIG. 3, a communication protocol in which transmission data transmitted to all amplifiers are included in one packet is assumed. Further, assumed is a communication system in which the number of connectable amplifiers is 4 in the related art, whereas among the 4 amplifiers (the amplifiers1to4), the transfer cycles of the amplifier3and the amplifier4are set to be double, as a result, two amplifiers (amplifiers3-1and4-1) are connectable.

In consequence, in the example of the numerical control system ofFIG. 3, the communication band used for communication of the numerical controller10and the amplifiers3and4in the related art is alternately used by the amplifier3and the amplifier3-1or the amplifier4and the amplifier4-1. Even when the numerical control system ofFIG. 3is used instead of the numerical control system of the related art including the four amplifiers, there is no influence on communication between numerical controller10and the amplifier1and communication between the numerical controller10and the amplifier2at all.

FIG. 4is a diagram illustrating an example of an amplifier side reception timing of transmission data from the numerical controller10to the amplifiers in the numerical control system ofFIG. 3(a start code is omitted).

Since there is a delay according to a line length or a delay in a circuit at the time of passing through amplifiers until a packet arrives at each amplifier, an arrival time of an amplifier distant from the numerical controller10is delayed.

In the system configuration of the related art illustrated inFIG. 7, since a maximum of the number of connectable amplifiers is assumed to be 4, up to 4 amplifiers are guaranteed to be able to perform reception within a cycle as in a “cycle2” ofFIG. 4. Meanwhile, the configuration of the numerical control system of the present invention illustrated inFIG. 3, the amplifier3-1and the amplifier4-1are added, and the reception timings of the amplifier3-1and the amplifier4-1may be included in the next cycle as in a “cycle1” ofFIG. 4. Similarly, even when the number of amplifiers is increased and a total line length of the system is increased, the amplifier3-1and the amplifier4-1can perform reception within a “cycle1of double cycle,” and the punctuality is maintained in the double cycle.

<Transmission from Amplifiers to the Numerical Controller10>

FIG. 5is a diagram illustrating an example of transmission from the amplifiers to the numerical controller10in the numerical control system according to the present invention.

In the example ofFIG. 5, similarly to the numerical control system ofFIG. 3, a communication protocol in which transmission data transmitted to all amplifiers are included in one packet is assumed. Further, assumed is a communication system in which the number of connectable amplifiers is 3 in the related art, whereas among the 3 amplifiers (the amplifiers1to3), the transfer cycles of the amplifier3is set to be double, and one amplifier (an amplifier4) is connectable.

In the numerical control system illustrated inFIG. 5, it is determined whether the amplifier3transmits its own data (data of the amplifier3) based on a current cycle number or transmits data of the amplifier4. In other words, the amplifier3serves to organize its own transfer and the transfer of the amplifier4. Since transfer data of the amplifier4is transferred to and held in the amplifier3in a “cycle1” and a “cycle3,” the amplifier3can transmit the transfer data of the amplifier4in a “cycle2” and a “cycle4.”

In communication in which the punctuality is guaranteed, since a communication delay between the numerical controller10and a slave at a farthest end has to be within a communication cycle in view of a delay in a circuit or a delay caused by a line length, when a communication cycle of the system is decided, a maximum of the number of connectable amplifiers and a maximum of a total line length are decided.

In the case of the numerical control system ofFIG. 5, the number of connectable amplifiers is assumed to be 3 in the related art, therefore the number of amplifiers in which the punctuality is guaranteed is 3. In other words, when the amplifier4is simply added, data transmitted by the amplifier4is not guaranteed to reach the numerical controller10in the same cycle, and if data transmitted by the amplifier4does not reach the numerical controller10in the same cycle, its transmission timing extends to the next cycle, as a result, there is a possibility that the transmission timing of data transmitted by the amplifier4competes against a transmission timing of data transmitted by another amplifier in the next cycle. On the other hand, in the example of the numerical control system ofFIG. 5, data transmitted by the amplifier4is first held in the amplifier3during the “cycle1,” and then transmitted by the amplifier3in the “cycle2”, therefore the transmission timing of data transmitted by the amplifier4does not compete against a transmission timing of data transmitted by another amplifier.

As described above, in the communication from the amplifiers to the numerical controller10, even when an amplifier is added, and the total line length is increased, the punctuality of N times the cycle is secured. Further, even when the numerical control system ofFIG. 5is used instead of the numerical control system of the related art including three amplifiers, there is no influence on communication between the numerical controller10and the amplifier1and communication between the numerical controller10and the amplifier2at all.

Further, a configuration in which a plurality of units (IO units) for external signal input and output is employed between the numerical controller10and a machine tool (not illustrated) in order to receive and output a DI/DO signal (an input signal/output signal), and the DI/DO signal is usually transferred between the numerical controller10and the IO units. The present invention can be applied to a system in which a plurality of IO units, instead of amplifiers, are connected to the numerical controller10in the daisy-chain manner.