Note: Descriptions are shown in the official language in which they were submitted.
CA 02818367 2014-01-28
INPUT/OUTPUT UNIT AND CONTROL SYSTEM
FIELD OF DISCLOSURE
[0001] The present invention relates to an input/output unit and a control
system.
BACKGROUND
[0002] A control system used in a workplace where the first priority is given
to safety
assurance, such as a chemical plant or a nuclear power plant, needs to clear
rigorous
requirements imposed on its availability (characteristics defined to indicate
how well the
1 0 particular system is able to withstand trouble, also referred to as an
availability factor),
since if the system goes down due to any type of trouble, a serious accident
may result.
Japanese laid open patent publication no. 2011-113415 discloses a technology
whereby
better availability is assured by connecting a plurality of RIO (remote
input/output) units
in a duplex circuit system achieved through a duplex CPU device configuration.
1 5 [0003] FIG. 5 is a block diagram showing the structure disclosed in
Japanese laid open
patent publication no. 2011-113415, i.e., a block diagram of the structure
that includes a
plurality of RIO (remote input/output) units (input/output units) in a duplex
circuit
system achieved through a duplex CPU device configuration. If an optical cable
S1
and an optical cable S4 become cut off from each other, the locations where
the
2 0 abnormality (error) has occurred must be detected through a two-step
procedure by first
detecting the error in the optical cable S4 and then detecting the error in
the optical cable
S1 only after the problem in the optical cable S4 has been corrected in the
structure
disclosed in Japanese Laid Open Patent Publication No. 2011-113415.
SUMMARY
2 5 [0004] According to the first aspect of the present invention, an
input/output unit
comprises: an input/output device that controls a control target device in
response to a
control request frame originating from a control device, and transmits, in
response to the
control request frame, a control response frame to the control device by
superimposing
the control response frame upon an electrical signal; a first conversion
device that is
30 included in a first system communication path and converts an optical
signal, upon
which the control request frame transmitted via the first system communication
path is
superimposed, to an electrical signal; a second conversion device that is
included in the
first system communication path and converts the electrical signal, upon which
the
control response frame is superimposed, to an optical signal; a third
conversion device
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that is included in a second system communication path and converts the
electrical signal,
upon which the control response frame is superimposed, to an optical signal;
and a
fourth conversion device that is included in the second system communication
path and
converts an optical signal, upon which the control request frame transmitted
via the
second system communication path is superimposed, to an electrical signal. The
first
conversion device transmits, in response to a status request frame originating
from the
control device, a status response frame including a reception status of the
optical signal
to the control device by superimposing the status response frame upon an
electrical
signal; the second conversion device converts the electrical signal with the
status
response frame superimposed thereupon, which is transmitted by the first
conversion
device, to an optical signal; the fourth conversion device transmits, in
response to a
status request frame originating from the control device, a status response
frame
including a reception status of the optical signal to the control device by
superimposing
the status response frame upon an electrical signal; and the third conversion
device
converts the electrical signal with the status response frame superimposed
thereupon,
which is transmitted by the fourth conversion device, to an optical signal,
obtains, from
the first conversion device, the reception status at the first conversion
device and
transmits, in response to a status request frame originating from the control
device, a
status response frame including the reception status at the first conversion
device to the
control device by superimposing the status response frame upon an optical
signal.
[0005] According to the second aspect of the present invention, a control
system
comprises: an input/output unit as previously described; and the control
device. The
control device decides that the first system communication path has a fault if
the control
device does not receive the status response frame returned by the first
conversion device
2 5 within a predetermined length of time following transmission of the
status request frame
to the first conversion device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 is a block diagram showing the structure of the control system
according
to the present invention.
[0007] FIG. 2 shows the structure of a communication frame.
[0008] FIG. 3 presents a communication time chart pertaining to communication
carried out under normal circumstances.
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[0009] FIG. 4 presents a communication time chart pertaining to communication
carried out in an error state.
[0010] FIG. 5 is a block diagram of the structure adopted in a control system
in the
prior art.
DETAILED DESCRIPTION
[0011] FIG. 1 shows the structure of a control system that includes RIO units
(input/output units) according to the present invention. The control system,
which
includes a CPU unit 5A, a CPU unit 5B, an RIO unit 1, an RIO unit 2 and an RIO
unit 3
is connected to a command device 4. The CPU unit 5A, the RIO unit 1, the RIO
unit 2
and the RIO unit 3 are individually connected with one another through optical
cables S1
through S4 and T1 through T4. The CPU unit 5B, the RIO unit 1, the RIO unit 2
and
the RIO unit 3 are individually connected with one another through optical
cables Ul
through U4 and V1 through V4. The CPU unit 5A, the CPU unit 5B and the command
device 4 are connected with one another via a command line 41.
[0012] The CPU unit 5A includes a CPU device (control device) A1 and electro-
optical
conversion devices A31 and A32. The CPU device A1 is connected to the
electro-optical conversion device A31 via a system-1 electrical cable A21 and
is also
connected to the electro-optical conversion device A32 via a system-2
electrical cable
A22. As will be described in detail later, the CPU device A1 transmits a
control request
frame addressed to an RIO device within an RIO unit or a status request frame
addressed
to an electro-optical conversion device within an RIO unit. It also receives a
control
response frame from the RIO device in the RIO unit or a status response frame
from the
electro-optical conversion device in the RIO unit. While request frames R,
including
2 5 the control request frame and the status request frame, and response
frames A, including
the control response frame and the status response frame, are each
superimposed upon
an electrical signal and transferred through an electrical cable, they are
each
superimposed upon an optical signal and transferred through an optical cable.
The
electro-optical conversion devices A31 and A32 each transmit a frame having
been
received through the electrical cable, toward the optical cable side and also
transmit a
frame having been received through the optical cable, toward the electrical
cable side.
Namely, the electro-optical conversion devices A31 and A32 each achieve
switchovers
between electrical signals and optical signals. upon which the request frames
R and the
response frames A are superimposed. While the electrical-side interface is
configured
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so as to enable integrated transmission/reception, transmission and reception
are carried
out independently of each other through the optical-side interface. Each
electro-optical
conversion device can be independently disengaged. This means that even when
the
electro-optical conversion device A31 connected to the system-1, for instance,
malfunctions and needs to be replaced, the system can operate without
interruption with
the electro-optical conversion device A32 connected to the system-2. The two
electro-optical conversion devices A31 and A32 are connected with each other
via a link
bus A33, which is an electrical cable enabling information exchange between
the two
electro-optical conversion devices A31 and A32.
[0013] The CPU unit 5B assumes a structure similar to that described above.
The
command device 4 controls the CPU device Al and a CPU device B1 via the
command
line 41, by designating either one as a main system and designating the other
as a
subsystem.
[0014] The RIO unit 1 includes an RIO device 11, and electro-optical
conversion
devices 121, 122, 141 and 142. The RIO device 11 is connected to the electro-
optical
conversion devices 121 and 141 through a system-1 electrical cable 131 and is
also
connected to the electro-optical conversion devices 122 and 142 through a
system-2
electrical cable 132. An operator 150 and a sensor 151 are connected to the
RIO device
11 and the operator 150 and the sensor 151 are also connected to a control
target device.
2 0 As are the electro-optical conversion devices included in the CPU
units, two of the
electro-optical conversion devices included in the RIO unit 1, i.e., the
electro-optical
conversion devices 121 and 122, are connected with each other via a link bus
123 and
the other two electro-optical conversion devices 141 and 142 in the RIO unit 1
are
connected with each other via a link bus 143. The RIO unit 2 and the RIO unit
3 adopt
structures similar to that of the RIO unit 1.
[0015] FIG. 2 shows a communication frame. A start flag Fl indicates a
starting
point of the frame. A CPU, an RIO or an electro-optical conversion device
receives a
frame bearing a recipient address F2 matching its own address but does not
receive any
frame with a recipient address that does not match its own address. It is to
be noted
3 0 that the CPUs, the RIOs and the electro-optical conversion devices are
each assigned
with a unique address different from any other address, except for two electro-
optical
conversion devices, one connected to the system-1, the other connected to the
system-2
and connected with each other via a link bus, which bear a single, common
address.
For instance, the electro-optical conversion device A3I and the electro-
optical
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conversion device A32 are assigned with a common address. The electro-optical
conversion device 121 and the electro-optical conversion device 122 also share
a single
address. A frame transmitted by a CPU, an RIO or an electro-optical conversion
device
bears its address in a sender address F3. In a type F4, information
distinguishing the
particular frame as a request frame (REQ) or a response frame (ACK) is
provided. A
circuit primary station transmits a request frame, and a circuit secondary
station responds
by transmitting a response frame. An RIO puts input data or output data in a
data F5.
In addition, two electro-optical conversion devices connected with each other
via a link
bus report a system-1 optical reception status and a system-2 optical
reception status to
each other at all times through data communication carried out via the link
bus. This
enables each electro-optical conversion device to possess the information on
the
reception statuses in both system 1 and system 2, which will indicate any
error in an
optical signal received through either system, at all times. As a result, the
electro-optical
conversion device is able to place the reception statuses indicating any error
in an optical
signal received through system 1 or system 2, in the data F5. For instance,
the
electro-optical conversion device 121 places the information on the system-1
optical
reception status corresponding to the optical cable Sl, having been collected
by the
electro-optical conversion device 121 itself, and the information on the
system-2 optical
reception status corresponding to the optical cable V1, having been collected
by the
electro-optical conversion device 122 connected to the electro-optical
conversion device
121 via the link bus, in the data F5. An end flag F6 indicates an ending point
of the
frame.
100161 When the CPU device A1 is designated as the main system device, the CPU
device Al acts as the circuit primary station that engages in communication
with the
secondary stations, i.e., the RIO devices 11, 21 and 31, so as to individually
prompt the
RIO devices 11, 21 and 31 to output data to the corresponding control target
devices via
operators 150, 250 and 350 respectively and to take in data from the control
target
devices via sensors 151, 251 and 351 respectively. The CPU device B1 takes in
(snoops on) the contents of communication in which the CPU device Al is
engaged.
The term "snoop", usually meaning "eavesdrop", is used in this context to mean
"monitor" a network or the like. The snoop operation is enabled through a
function of
the electro-optical conversion devices 121 and 342 that allows them to
constantly
transmit a frame, addressed to the CPU device A1 and received through the
optical side,
toward both the optical side (the side on which the optical cables Ul and V4
are
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=
connected) and the electrical side (the side on which the system-1 electrical
cable 131 is
connected). The snoop operation is enabled as the frame addressed to the CPU
device
A1 is transmitted to the CPU device B1 via the optical cables Ul and V4. A
similar
function is provided through the electro-optical conversion devices 122 and
341 when
the CPU device B1 is designated as the main system CPU device. Since the
electro-optical conversion devices 121, 122, 341 and 342 fulfill a unique
function
different from that of the other electro-optical conversion devices, they are
each notated
as E/O-RC in FIG. 1. In addition, the electro-optical conversion devices A31,
A32,
B31 and B32 within the CPU units 5A and 5B, which are also distinct from the
other
electro-optical conversion devices E/O, are each notated as E/O-CP in FIG. 1.
[0017] FIG. 3 presents a communication time chart pertaining to a
communication
frame transmission/reception that may be executed at the CPU unit 5A under
normal
circumstances. The communication is executed cyclically. The CPU device
engages
in communication with an RIO device, a system-1 electro-optical conversion
device and
a system-2 electro-optical conversion device. The CPU device transmits a
single
request frame R both through the system 1 circuit and the system 2 circuit,
whereas the
RIO device transmits a single response frame A both through the system 1
circuit and the
system 2 circuit. First, the CPU device transmits a request frame R addressed
to an
RIO device via the optical cable S1 in the system-1 circuit and via the
optical cable 14 in
the system-2 circuit. The request frame R, having been transmitted from the
CPU
device as described above, is then transferred via the electro-optical
conversion devices
and sent back to the CPU device. However, since the communication frame bears
an
address different from its own address, the CPU device does not receive the
returning
request frame. Next, the CPU device receives a response frame A transmitted
from the
RIO device and addressed to the CPU device, via the optical cable S4 in the
system-1
circuit and via the optical cable T1 in the system-2 circuit.
[0018] Subsequently, the CPU device transmits a request frame R addressed to a
system-1 electro-optical conversion device via the optical cable S1 in the
system-1
circuit and transmits a request frame R addressed to a system-2 electro-
optical
conversion device via the optical cable 14 in the system-2 circuit. The
request frames
R, having been transmitted by the CPU device as described above, are
transferred via the
electro-optical conversion devices and sent back to the CPU device. However,
the
request frames do not bear addresses matching its own address and thus, the
CPU device
does not receive either of the returning request frames. The electro-optical
conversion
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devices each transmit a frame through the circuit in which the particular
electro-optical
conversion device is connected. The CPU device receives a response frame A.
originating from the system-1 electro-optical conversion device and addressed
to the
CPU device, via the optical cable S4 in the system-1 circuit and receives a
response
frame A, originating from the system-2 electro-optical conversion device and
addressed
to the CPU device, via the optical cable T1 in the system-2 circuit. The time
chart in
FIG. 3 indicates how such communication is carried over a single cycle. While
FIG. 3
presents an example of communication carried out by the CPU device with a
single RIO,
a single system-1 electro-optical conversion device and a single system-2
electro-optical
1 0 conversion device connected thereto, the CPU device may be in fact
connected with
multiple RIO devices, system-1 electro-optical conversion devices and system-2
electro-optical conversion devices. In such a case, communication will be
carried out
repeatedly multiple times, each in correspondence to one of the communication
partners
connected to the CPU device. Such communication is indicated with dotted lines
in FIG.
3. The electro-optical conversion devices (E/Os, E/O-RCs and E/O-CPs) each
transmit
a response frame through the two circuits, i.e., the optical circuit and the
electrical circuit,
so as to report the optical reception status to the two CPU devices, the CPU
device A1
and the CPU device BI.
[0019] FIG. 4 presents a communication time chart pertaining to communication
carried out in a state of error. In this "state of error", the optical cables
S1 and S4 in
FIG. I both have a fault. While normal transmission/reception can be carried
out in
system 2, full frame reception cannot be achieved in system 1. After
transmitting a
control request frame or a status request frame, the CPU device A 1 waits in
standby to
receive a control response frame from the RIO device or a status response
frame from
2 5 the electro-optical conversion device. If it does not receive the
control response frame
or the status response frame within a predetermined length of time, it
terminates the
reception. At this time, a response timeout is detected. The time to elapse
between
the request frame transmission and the response timeout detection is set as a
response
timeout length. The response timeout length is set so as to assume a value
equal to or
3 0 greater than the maximum value representing the length of time allowed
to elapse after
the request frame is transmitted until the response frame is received when the
optical
cables S1 and S4 are both in a normal state. Based upon the response timeout
detected
as described above, the CPU device Al decides that the system-1 communication
path
constituted with the optical cables Sl, S2, S3 and S4, i.e., the system-1
communication
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path that includes the electro-optical conversion devices 121 and 141, has a
fault.
Based upon this decision. the CPU device A1 is then able to shift into
processing for
transmitting the next control request frame or status request frame. Likewise,
if the
system-2 communication path, constituted with the optical cables 11, 12, 13
and 14, i.e.,
the system-2 communication path that includes the electro-optical conversion
devices
142 and 122, has a fault, the CPU device A1 is able to decide that the system-
2
communication path has a fault based upon a response timeout detected in a
similar
manner. Upon making such a decision, the CPU device A1 is able to shift into
processing for transmitting the next control request frame or status request
frame
regardless of which system communication path has the fault.
[0020] As shown in FIG. 1, the RIO unit (input/output unit) 1 according to the
present
invention includes the RIO device 11, the electro-optical conversion device
121, the
electro-optical conversion device 141, the electro-optical conversion device
122 and the
electro-optical conversion device 142. The RIO device 11 controls the control
target
device in response to a control request frame R originating from the CPU
device A 1 and
transmits, in response to the control request frame R, a control response
frame A to the
CPU device Al by superimposing it upon an electrical signal. The electro-
optical
conversion device 121, which is included in the system-1 communication path,
converts
an optical signal upon which the control request frame R transmitted via the
system-1
communication path, is superimposed, to an electrical signal, and transmits,
in response
to a status request frame R originating from the CPU device A 1, a status
response frame
A, including the optical signal reception status, to the CPU device Al by
superimposing
the status response frame A upon an electrical signal. The electro-optical
conversion
device 141 converts the electrical signal upon which the control response
frame A is
superimposed, to an optical signal, and also converts the electrical signal
upon which the
status response frame A is superimposed, transmitted by the electro-optical
conversion
device 121, to an optical signal. The electro-optical conversion device 122,
which is
included in the system-2 communication path, converts an optical signal upon
which the
control request frame R transmitted via the system-2 communication path, is
superimposed, to an electrical signal, and also converts an electrical signal
upon which a
status response frame A is superimposed, transmitted by the electro-optical
conversion
device 142, to an optical signal. The electro-optical conversion device 122
further
obtains, from the electro-optical conversion device 121, the reception status
at the
electro-optical conversion device 121, and transmits, in response to the
status request
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frame R originating from the CPU device Al, the status response frame A
including the
reception status at the electro-optical conversion device 121. to the CPU
device A 1 by
superimposing the status response frame A upon an optical signal. The electro-
optical
conversion device 142, which is included in the system-2 communication path,
converts
the optical signal upon which the control request frame R, transmitted through
the
system-2 communication path, is superimposed, to an electrical signal, and
also
transmits, in response to the status request frame R originating from the CPU
device Al,
a status response frame A including the optical signal reception status, to
the CPU device
Al by superimposing the status response frame A on an electrical signal. This
means
that even when the optical cables S1 and S4 are both cut off, the CPU device
Al is able
to detect, based upon the status response frame A originating from the electro-
optical
conversion device 122 and addressed to the CPU device Al, that the optical
cable S1 has
a fault. In other words, the present invention provides an RIO unit
(input/output unit)
that makes it possible to determine a specific location where a circuit fault
has occurred.
[0021] In the embodiment described above, data are transmitted and received
via the
link buses at all times. However, the present invention is not limited to this
example.
For instance, upon receiving a request frame originating from the CPU device,
an
electro-optical conversion device may output a status inquiry command, which
includes
a request for data indicating the optical reception status in the other
system, to the
electro-optical conversion device in the other system via the link bus, and
receive a
status report response, which includes data indicating the optical reception
status in the
other system, transmitted in response. In
this case, the need for constantly reporting
the optical reception status in the system-1 and the optical reception status
in the
system-2 to each other, will be eliminated, making it possible to achieve
better efficiency
in conserving the performance level of the data communication processing via
the link
bus. The electro-optical conversion device will then transmit a response
frame,
prepared in response to the request frame originating from the CPU device,
which
carries the optical reception status in the other system obtained as described
above, as
well as the optical reception status in the subject system, to the CPU device.
[0022] Before a switchover between the main system CPU device (CPU device Al)
and the subsystem CPU device (CPU device B1) occurs, fault information
indicating any
malfunction occurring in any of the optical cables Ul through U4 can be
collected via
the system-2 circuit through data communication enabled via the link buses
connecting
the electro-optical conversion devices connected in the system-1 and the
electro-optical
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conversion devices connected in the system-2. The fault information indicating
a
malfunction in any of the optical cables Ul through U4, collected by the CPU
device B1
as described above, is then provided to the command device 4. As a result, the
operator
of the command device 4 is able to cancel the CPU device system switchover, so
as to
preempt a communication failure that would otherwise occur immediately after
the
switchover and would ultimately disable control of the control target by the
CPU device.
100231 The status of the subsystem CPU device B1 is synchronized with that of
the
main system CPU device Al on a regular basis in preparation for a CPU device
system
switchover. The electro-optical conversion device 121, in turn, transmits, in
response
1 0 to the status request frame R originating from the CPU device Al , a
status response
frame A including the optical signal reception status to the CPU device Al by
superimposing the status response frame A upon an electrical signal, and also
transmits
the status response frame A including the reception status to the CPU device
B1 via the
optical cable Ul by superimposing the status response frame A upon an optical
signal.
In addition, the electro-optical conversion device 123 obtains, from the
electro-optical
conversion device 121, the reception status at the electro-optical conversion
device 121,
transmits, in response to the status response frame R originating from the CPU
device
A1, a status response frame A, which includes the reception status at the
electro-optical
conversion device 121, to the CPU device A1 by superimposing the status
response
2 0 frame A upon an optical signal, and also transmits the status response
frame A, which
includes the reception status at the electro-optical conversion device 121 to
the
subsystem CPU device Bl, the status of which is synchronized with the status
of the
CPU device Al, by superimposing the status response frame A upon an electrical
signal.
The status response frame A including the reception status at the electro-
optical
2 5 conversion device 121 superimposed upon the electrical signal is
superimposed upon an
optical signal at the electro-optical conversion device 342 and is transmitted
to the
subsystem CPU device B1 via the optical cable V4. Through these measures, the
CPU
device B1 is able to snoop on the response frame transmitted from the electro-
optical
conversion device to the CPU device Al, which makes it possible to identify
the fault
30 location sooner than would be possible through regular status
synchronization.
[0024] The above described embodiment is an example, and various modifications
can
be made without departing from the scope of the invention.
