Servo control unit

Abstract

Servo control device (100) comprising a command receiving unit (110) configured to asynchronously receive a command at each command reception period, which is issued by a control device (200) at each command update period, and a servo control calculation unit (120) configured to control a motor in response to the command, - wherein the command receiving unit (110) asynchronously receives a counter in a measurement mode for each command reception period, which is output by the control unit (200) for each command update period, - comprising the servo control device (100): - an event recording unit (111) configured to detect, in measurement mode, the occurrence of an event that causes fluctuations in the meter's reception intervals, - a deviation calculation unit (112) configured to calculate, based on an event occurrence period and the command reception period in measurement mode, a deviation amount between respective clock cycles of the control device (200) and the servo control device (100), wherein the deviation amount represents a progression of time at each command reception period, output by the clock cycle of the servo control device (100), with respect to a time specified by the clock cycle of the control device (200). 1 , and - a receive period setting unit (114) configured to set the command receive period based on the amount of deviation in an operating mode.

Description

Background of the inventionField of the invention

[0001] The present invention relates to a servo control device, and more particularly to a servo control device in which fluctuations of command reception intervals can be improved. Description of the related prior art

[0002] Motion systems for asynchronous communication between a control device as a motion control device (e.g. a numerical control device) and a servo control device (e.g. a servo drive) are known, as in Fig. 1 (see Japanese Patent Application Laid-Open Nos. 2006-350768 and 2008-176673). In these motion systems, the controller outputs a command at a specified time, and a command receiving unit of the servo controller receives the command within the specified time. A servo control calculation unit drives a motor in response to the received command. A pulse generator feeds a position or speed back to the servo control calculation unit.

[0003] In motion systems of this type, even though the controller performs a command update (or command output) within the specified time period, the servo controller may sometimes be unable to receive the command within the specified time period. In particular, a phenomenon periodically occurs that the command reception time is shifted by a period corresponding to one operating cycle of the servo controller.

[0004] Fig. Figure 2 shows a specific example. The control device periodically updates the command according to a command update period M. The servo control device periodically attempts to receive the command according to a command reception period S. For example, if the command update period M is set by M = S (command reception period) x 3, the servo control device should theoretically be able to receive the command without exception every third command reception period. In reality, however, as shown in Fig. 2, in each specified period, the phenomenon occurs that the command is received at the fourth, not the third, command reception period.

[0005] The main reason for the occurrence of such a phenomenon may be that the control device and the servo control device have their own independent clocks. Although it is ideal if the respective clocks of the two devices are completely consistent with each other in terms of reference time and clock intervals, they are actually subject to small deviations. When these deviations accumulate and when the accumulated deviations exceed the command reception period S, the above phenomenon inevitably occurs.

[0006] The controller and the servo controller perform control based on the assumption that the command is updated and received within the specified time period. Therefore, if the servo controller fails to receive the command within the specified time period, the motor speed or position commanded by the controller will not match the speed or position of the motor driven by the servo controller, inevitably resulting in a decrease in positioning accuracy. Furthermore, the response time from the command update until the servo controller receives the command and drives the motor will be undesirably delayed.

[0007] Fig. Figure 3 shows the result of a comparison between a motor speed (solid line) based on a motion command issued by the controller and a motor speed (dashed line) based on the command received by the servo controller at a specific time. When command reception is performed within a completely fixed period in the servo controller, that is, when the command update period M is exactly an integer multiple of the command reception period S, the two speeds should initially match each other.When the command reception in the servo controller experiences a deviation of one period, a difference equal to (1 x command reception period S) is inevitably generated between the motor speed (solid line) based on the movement command issued by the controller and the motor speed (dashed line) based on the command received by the servo controller, as shown by the circle. Fig. 3 the speed command is given as an example, the same problem can also be caused by the position command.

[0008] JP 2013-62928 A discloses a control system for controlling a drive device in synchronization with a control cycle of a control device. The control system is configured to determine a number of periods of the drive device to be adjusted that are within a period of the control device.

[0009] The present invention has been made to solve these problems and aims to provide a servo control device in which fluctuations of command reception intervals can be improved. Summary of the invention

[0010] A servo control device according to the present invention is provided in claim 1. The servo control device comprises a command receiving unit configured to asynchronously receive, at each command receiving period, a command issued by a controller at each command update period, and a servo control calculation unit configured to control a motor in response to the command. In a measurement mode, the command receiving unit asynchronously receives, at each command receiving period, a counter output by the controller at each command update period.The servo control device includes an event detection unit configured to detect, in the measurement mode, the occurrence of an event that causes fluctuations in reception intervals of the counter, a deviation calculation unit configured to calculate a deviation amount between respective clocks of the control device and the servo control device based on an occurrence period of the event and the command reception period in the measurement mode, and a reception period setting unit configured to set the command reception period based on the deviation amount in an operation mode.

[0011] In the servo control device according to one embodiment of the present invention, the setting time of the command reception period by the reception period setting unit is an integer multiple of a minimum clock value of the servo control device.

[0012] In the servo control device according to one embodiment of the present invention, the phase of the command reception period after being set by the reception period setting unit is shifted by substantially half a period length from that before the setting.

[0013] The servo control device according to one embodiment of the present invention further includes a deviation buffer unit configured to store the deviation amount.

[0014] According to embodiments of the present invention, a servo control device can be provided in which fluctuations of command reception intervals can be improved. Brief description of the drawings

[0015] The above and other objects and features of the present disclosure will become apparent from the description of the embodiments with reference to the accompanying drawings. Fig. 1 is a diagram showing the structure of a motion system including a servo control device; Fig. 2 is a diagram showing the operation of a motion system including a conventional servo control device; Fig. 3 is a diagram showing the operation of the motion system including the conventional servo control device; Fig. 4 is a diagram showing a method in which the servo control device calculates deviation amounts; Fig. 5 is a diagram showing a method in which the servo control device calculates deviation amounts; Fig. 6 is a diagram showing the operation of a motion system including a servo control device according to Example 1; Fig. 7 is a diagram showing the operation of the motion system including the servo control device according to Example 1; Fig. 8 is a diagram showing the operation of a motion system including a servo control device according to Example 2; Fig. 9 is a diagram showing the operation of the motion system including the servo control device according to Example 2; Fig. 10 is a diagram showing the structure of a motion system including a servo control device; and Fig. 11 is a diagram showing another example of the structure of the motion system including the servo control device. Detailed description of the preferred embodiments

[0016] The following is a description of the operation of a servo controller 100 according to embodiments of the present invention. The servo controller 100 includes a device for detecting and correcting fluctuations in command reception intervals. The servo controller 100 has two operating modes: a measurement mode and an operation mode.

[0017] The measurement mode is a mode for calculating the amount of deviation between the respective timings of a controller 200 and the servo controller 100 before an actual command-based operation. It is assumed that the following relationship between the respective command update periods of these two devices is stored in advance in the servo controller 100. Command update period M = command reception period S xa (a = 1, 2, 3...)

[0018] A method for calculating the amount of deviation between the respective clocks of the two devices is described with reference to Fig. 4 and Fig. 5. The control device 200 periodically outputs a signal called a counter instead of the command. The counter output period is the command update period M. The servo control device 100 periodically attempts to receive the counter. The reception attempt period is the command reception period S. In most cases, the servo control device 100 receives the counter at each of a number of reception attempts. However, as the clock deviation accumulates, a phenomenon (hereinafter referred to as an "event") occurs that the counter cannot be received at each of a number of reception attempts. Specifically, when the event occurs, the servo control device 100 receives the counter at an (a + 1)-th (see Fig. 4) or an (a - 1)-th (see Fig. 5) Reception attempt since the last reception. The event occurrence has a periodicity, and its period repeats every x number of counter updates. The servo controller 100 measures this period x. A deviation amount t is calculated from the event occurrence period x and the command reception period S according to the following equations. The deviation amount t represents the progression of time at each command reception period S specified by the clock of the servo controller 100 with respect to a time specified by the clock of the controller 200. Note that the clock of the servo controller 100 is faster when the deviation amount t is positive and slower when the deviation amount t is negative.

[0019] In the case where the servo controller 100 receives the counter, if a number (a + 1) of reception attempts are performed for each number x of counter updates (see Fig. 4), the deviation amount t can be represented by the following equation: t=S / (x×a)(reception interval>a).

[0020] In the case where the servo controller 100 receives the counter, if a number (a - 1) of reception attempts are performed for each number x of counter updates (see Fig. 5), the deviation amount t can be represented by the following equation: t=−S / (x×a)(Reception interval <a).

[0021] The operation mode is a mode in which the operation is performed based on the actual command issued by the controller 200. Based on the timing deviation amount calculated in the measurement mode, the servo controller 100 adjusts the command reception period S so that the event no longer occurs every time a command is received. Specifically, the servo controller 100 changes the length of the command reception period S.

[0022] Deviation amounts D n at an nth command reception in the servo control device 100 can be represented by the following equation: Dn=t+Rn−1, where t is a deviation amount for each command reception period S and R n-1 Deviation amounts (hereinafter referred to as "carry-over times") that could not be set at the last or (n - 1)th command reception.

[0023] Of the amounts D nA deviation amount (hereinafter referred to as "setting time") that can be set at the nth command reception depends on a minimum clock value T. The minimum clock value T is a clock period that defines the timing of each processing of the servo controller 100 and represents a minimum time unit for setting the length of the command reception period S. Thus, the setting time is an integer multiple of the minimum clock value T and can be represented as follows: Response time=Qn×T, where Q n an integer part of the quotient of D n / T is.

[0024] The servo controller 100 adds the calculated adjustment time to the command reception period S. The length of the command reception period S is then adjusted. The deviation amounts that could not be adjusted at the nth command reception are treated as carryover times at the next or (n + 1)th command reception. Carryover times R n for the (n + 1)th command reception can be represented as follows: Rn=Dn−(Qn×T).

[0025] According to these processing steps, the reception period is set in units of the minimum clock value T at each command reception. Thereby, the accumulation of the deviation amount t between the respective clocks of the controller 200 and the servo controller 100 is eliminated as necessary, so that the occurrence of the event is suppressed.

[0026] Since the deviation amount t does not change even when a motion system 1 including the servo controller 100 is restarted, recalculation is unnecessary. However, the processing start time changes. Therefore, after the restart, the time of the next event occurrence should be predicted once in the measurement mode, which is to be switched to the operation mode to set the command reception period S.

[0027] Fig. 10 is a block diagram showing the structure of a motion system 1 including a servo controller 100 according to an embodiment of the present invention. The motion system 1 includes the servo controller 100, a controller 200, a motor 300, and a pulse generator 310.

[0028] The controller 200 is a host controller, such as a numerical control device or PLC (programmable logic controller). The controller 200 outputs a counter in measurement mode and position and speed commands in operation mode to the servo controller 100.

[0029] The servo control device 100 includes a command receiving unit 110, an event detecting unit 111, a deviation calculating unit 112, a deviation buffering unit 113, a receiving period setting unit 114, and a servo control calculating unit 120.

[0030] The command receiving unit 110 receives the counter or commands, such as the position and speed commands, output by the controller 200.

[0031] In the measurement mode, the event detection unit 111 detects the occurrence of the event in the servo control device 100.

[0032] In the measurement mode, the deviation calculation unit 112 calculates the relative deviation amount t between the respective internal clocks of the controller 200 and the servo controller 100 based on the event occurrence period x (in which the event occurs every x number of counter updates) and the command reception period S.

[0033] The deviation buffer unit 113 temporarily stores the deviation amount t calculated by the deviation calculation unit 112 in the measurement mode.

[0034] In the operation mode, the reception period setting unit 114 sets the command reception period S based on the deviation amount t stored by the deviation buffer unit 113, thereby suppressing the occurrence of the event.

[0035] The servo control calculation unit 120 outputs a command pulse signal in response to a command for the motor 300. The motor 300 is driven at a rotation angle and speed corresponding to the command pulse signal. The encoder 310 detects the rotation angle and speed of the axis of the motor 300 and feeds them back to the servo control calculation unit 120 as encoder signals. The servo control calculation unit 120 performs feedback control based on the encoder signals, thereby adjusting the command pulse signal.

[0036] A specific operation example of the servo controller 110 is disclosed as an example. Example 1

[0037] The operation of a motion system 1 comprising a servo control device 100 according to Example 1 is described with reference to Fig. 6 and Fig. 7. In the measuring mode, the control device 200 outputs, as shown in Fig. 6, the counters were off in the command update period M ≈ 1 ms. Before adjustment or in the measurement mode, the servo controller 100 attempted to receive the counters in the command reception period S = 250 µs. Consequently, events with long command reception intervals occurred periodically, resulting in x = 5,000 and a = 4. Thus, the command reception unit 110 received the counter in most cases every fourth reception attempt, but in rare cases, it received the counter on the fifth reception attempt (event occurrence). An event occurred every 5,000th command update. Consequently, the deviation calculation unit 112 calculated the deviation amount t for each command reception period S as 12.5.

[0038] In the operation mode, the reception period setting unit 114 of the servo control device 100 has the deviation amount D n , the setting amount Q n and the transfer time R n calculated. Fig. 7 shows changes in the calculated deviation amount D n , the setting amount Q n and the transfer time R n . In command reception cycles (marked by stars) with the setting amount Q n of 1, the command reception period S was set in units of the minimum clock value T = 20 ns, so that the accumulation of the deviation amount was partially eliminated. It is therefore understood that the deviation amount D n was reduced in the next command reception cycle.

[0039] As in Fig. As shown in Figure 6, after adjustment or in the operating mode, the servo controller 100 has set the command reception period S to 250 µs + 20 ns in the command reception cycles marked by asterisks. Since no adjustment is made in the unmarked command reception cycles, the command reception period S remains at 250 µs. The accumulation of the clock deviation amount t has been eliminated, if necessary, by this adjustment. Thus, no event has occurred in the operating mode.

[0040] Preferably, the servo control device 100 should be as shown in Fig. 6, the phase of the command reception period after adjustment can be shifted by approximately a / 2 from that before adjustment by interrupting when the measurement mode transitions to the operation mode, that is, when the adjustment is started. In this way, command reception can be started at a time when an event is least likely to occur. In addition, this interruption should preferably be performed at a time one cycle or more before a command reception cycle in which the occurrence of the event is expected. This can ensure a processing time for setting the command reception period S, so that the mode can be smoothly switched to the operation mode. Example 2

[0041] The operation of a motion system 1 comprising a servo control device 100 according to Example 2 is described with reference to Fig. 8 and Fig. 9. In the measuring mode, the control device 200 outputs, as shown in Fig. 8, the counters were output in the command update period M ≈ 1 ms. Before adjustment or in the measurement mode, the servo controller 100 attempted to receive the counters in the command reception period S = 250 µs. Consequently, events occurred periodically with short command reception intervals, resulting in x = 5,000 and a = 4. Thus, the command reception unit 110 received the counter in most cases every fourth reception attempt, but in rare cases, it received the counter on the third reception attempt (event occurrence). An event occurred every 5,000th command update. Consequently, the deviation calculation unit 112 calculated the deviation amount t for each command reception period S as 12.5.

[0042] In the operation mode, the reception period setting unit 114 of the servo control device 100 has the deviation amount D n, the setting amount Q n and the transfer time R n calculated. Fig. 9 shows changes in the calculated deviation amount D n , the setting amount Q n and the transfer time R n . In command reception cycles (marked by stars) with the setting amount Q n of -1, the command reception period S was set in units of the minimum clock value T = 20 ns, so that the accumulation of the deviation amount was partially eliminated. It is therefore understood that the absolute value of the deviation amount D n was reduced in the next command reception cycle.

[0043] As in Fig. As shown in Figure 8, after adjustment or in the operating mode, the servo controller 100 sets the command reception period S to 250 µs - 20 ns in the command reception cycles marked by asterisks. Since no adjustment is made in the unmarked command reception cycles, the command reception period S remains at 250 µs. The accumulation of the clock deviation amount t has been eliminated, if necessary, by this adjustment. Thus, no event has occurred in the operating mode.

[0044] Preferably, the servo control device 100 should also be in Example 2, as in Fig. 8, the phase of the command reception period after adjustment can be shifted by approximately a / 2 from that before adjustment by interrupting when the measurement mode transitions to the operation mode, that is, when the adjustment is started. In this way, command reception can be started at a time when an event is least likely to occur. In addition, this interruption should preferably be performed at a time one cycle or more before a command reception cycle in which the occurrence of the event is expected. This can ensure a processing time for setting the command reception period S, so that the mode can be smoothly switched to the operation mode.

[0045] According to the present embodiment, even when the command update by the controller 200 and the command reception by the servo controller 100 are asynchronous, the servo controller 100 calculates the deviation amount between the respective clocks of these two devices and adjusts the command reception period based on the deviation amount. Thus, the servo controller 100 can suppress fluctuations in the command reception intervals. Consequently, a mismatch between the command issued by the controller 200 and the actual command to be issued by the servo controller 100 can be reduced, thus improving responsiveness. Furthermore, positioning accuracy is improved. Furthermore, machining accuracy is improved to reduce the defect rate, thus increasing productivity.In addition, a test facility can be operated stably.

[0046] The present invention is not limited to the embodiment described above, and various changes may be made without departing from the spirit of the invention. As in Fig. For example, as shown in Figure 11, a plurality of servo control devices 100 may be connected to the control device 200. In this case, the processing described in connection with the above embodiment is performed between the control device 200 and the individual servo control devices 100.

Claims

[1] A servo control device (100) comprising a command receiving unit (110) configured to asynchronously receive, at each command receiving period, a command issued by a control device (200) at each command update period, and a servo control calculation unit (120) configured to control a motor in response to the command, - wherein the command receiving unit (110) in a measurement mode asynchronously receives a counter for each command receiving period, which counter is output by the control device (200) for each command update period, - wherein the servo control device (100) comprises: - an event detection unit (111) configured to detect, in the measurement mode, the occurrence of an event causing fluctuations in the reception intervals of the counter, - a deviation calculation unit (112) configured to calculate, based on an occurrence period of the event and the command reception period in the measurement mode, a deviation amount between respective clocks of the control device (200) and the servo control device (100), wherein the deviation amount represents a progression of a time at each command reception period output by the clock of the servo control device (100) with respect to a time indicated by the clock of the control device (200) 1 , and - a reception period setting unit (114) configured to set the command reception period based on the deviation amount in an operation mode. [2] The servo control device (100) according to claim 1, wherein the setting time of the command reception period by the reception period setting unit (114) is an integer multiple of a minimum clock value of the servo control device (100). [3] The servo control device (100) according to claim 1, wherein the phase of the command reception period after being set by the reception period setting unit (114) is shifted by substantially half a period length from that before the setting. [4] The servo control device (100) according to claim 1, further comprising a deviation buffer unit (113) configured to store the deviation amount.

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