JPS6220561B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preventing a control device from malfunctioning due to noise in a device controlled by a computer, particularly a microcomputer.

2. Description of the Related Art Conventionally, a circuit as shown in FIG. 1 has been used to prevent malfunctions of a print start button or the like of a copying machine. In other words, the start signal Q from the flip-flop FF is prevented from being output due to the closing of the switch s, which lasts only for a time shorter than the time constant determined by the resistance r and the capacitance c, or the occurrence of a noise pulse. . Note that I is an inverter. In order to identify noise in an electric circuit and prevent malfunctions in the control device, as in this circuit, a considerable number of logic elements are required, resulting in a complex structure, which can lead to high costs and reduced reliability. becomes.

On the other hand, microcomputers have recently been developed,
As it has become possible to centrally control the operation timing of copying machines, etc. using microcomputers, it has become possible to identify the true control signal and eliminate noise generated inside and outside the copying machine, switch chatter, etc. In order to prevent malfunctions, using an appropriate combination of software and hardware is very effective in terms of making control devices such as copying machines more compact, easier to maintain, and reducing the number of parts.

The present invention has been made in view of the above points, and will be described in detail below with reference to the drawings.

FIG. 2 is a schematic diagram of the main parts of an embodiment of the present invention.
is a microcomputer built into the control device (hereinafter referred to as microcomputer), 2 is a switch for commanding various operations of the machine, and 3 is an operation command signal P3.
4 is a sampling signal output terminal that generates a sampling signal P4 that detects the open/closed state of switch 2, 5 is an input terminal for a signal P5 that represents the open/closed state of switch 2, and 11 and 12 are memory and It is a counter.

Next, the operation of the embodiment of the present invention will be explained with reference to FIGS. 2 to 4. A sampling pulse P4 having a constant interval t is constantly outputted from the terminal 4, and the switch 2 is, for example, a start switch for a controlled machine, and when the switch 2 is open, the operation command signal P3 is 0, and the switch 2 Assume that it becomes 1 in the closed state of . When the switch 2 is now closed at time _T1 from the state where the switch 2 is open, that is, the command signal P3 is 0,
One sampling pulse P4=1 is input to the input terminal 5 of the microcomputer 1 (steps in Fig. 3).
S1). This input is stored in the memory 11, and the memory content M is set to 1 (step S2). The sampling pulse immediately returns to 0 (step S3). In step S4, the microcomputer 1 checks whether the command signal P3 is 0 or 1. Since the command signal P3 is still 0 according to the above assumption, 1 is added to the counter 12 in step S6 after passing through the next step S5.
In this case, the count value C becomes 1. The count value is compared with the preset value N ₁ (N ₁ = 5 in this example) (step S7), but since they are not equal, it is set to 1.
It waits for the sampling interval t or performs other work (step S17). After the interval t, the sampling pulse P4 is generated again, and the value C of the counter 12 is changed through each of the steps described above.
is counted up to 2. By repeating the above operations, when the value C of the counter 12 becomes equal to the preset value _N1 , the operation command signal P3 is switched from 0 to 1 (step S8), and at the same time the counter 12 is cleared (step S9). When switch 2 is opened at time T ₂ , the sampling signal P
Since 4 is no longer input to microcontroller 1, P5 becomes 0.
Then, in step S2, the content M of the memory 12 becomes 0.
be made into At this time, since the operation command signal P3 is 1, the process passes through step S10, and in step S11, 1 is added to the counter and the value C becomes 1. In this state, the preset value N ₂ (in this example, N ₂ = 6
) has not been reached (step S1).
2) The system waits until the next sampling period or performs other work (step S17). After the interval t, the sampling pulse P4 is generated again, and the value C of the counter 12 is counted up to 2 by performing the same calculation. By repeating this process, when the value of the counter 12 becomes equal to the preset value _N2 , the operation command signal P3 is changed from 1 to 0 in step S13.
At the same time, the counter 12 is cleared (step S14).

Next, as shown in period A in Fig. 4, if the switch 2 is accidentally closed for a short time while it is open, or if a pulse is applied to the input terminal 5 of the microcomputer due to electrical noise, , P
Since 3 is 0, steps S4 to S in FIG.
6, the process proceeds to S7, but the input signal P5 becomes 0 before the value C of the counter 12 reaches _N1 , and the content M of the memory 11 becomes 0, so the counter 12 is cleared in step S15 and returns to the initial state. , the command signal P3 will not be switched to 1 by mistake. Furthermore, as shown in period B in FIG. 4, if the switch 2 is accidentally opened while it is closed, or if a 0 pulse is applied to the microcomputer input terminal 5 due to electrical noise,
Since P3 is 1, steps S4 to S10, S
11, the process proceeds to S12, but as before, the input signal P5 becomes 1 before the value C of the counter 12 reaches _N2 , and the content M of the memory 11 becomes 1, so the counter 12 is cleared in step S16 and the initialization is completed. state, and the command signal P3 is mistakenly set to 0.
It is never switched to.

FIG. 5 is a functional block diagram of the embodiment, in which the same reference numerals as in FIG. 2 represent the same or equivalent parts. This will be explained below.

The sampling pulse P4 generated by the sampling pulse generating means 21 is supplied to the AND circuit 22 together with a signal representing the open/closed state of the switch 2. The output of the AND circuit 22 (which obviously corresponds to the microcomputer input P5 in FIG. 2) is input to the exclusive OR circuit 23 together with the operation command P3, which is the signal at the output terminal 3. The logic output of the exclusive OR circuit 23 is directly supplied to the input terminal of the counter 12, and is also supplied to the inverter 24.
Resetting (clearing) the counter 12 via
Supplied to terminal R.

Therefore, when the two inputs to the exclusive OR circuit 23 are equal, the counter 12 is cleared, and when the two inputs are not equal, the count value of the counter 12 is incremented by one. The count value of the counter 12 is supplied to a comparator 25,
There, it is compared with the value preset in the reference value setting means 26 (this corresponds to the preset value _N1 or _N2 mentioned above). When the count value of the counter 12 increases and exceeds the preset value, the comparator 25 outputs a control signal and the command signal inverting means 27
is driven to invert the command signal at the operation command output terminal 3.

Note that the reference value set in the reference value setting means 26 can also be switched as shown by the dotted line in FIG. 5 in accordance with the command signal P3.

As described above, in the present invention, the logical product of the sampling pulse P4 and the microcomputer input P5 representing the open/closed state of the switch 2 is taken, and the operation is performed only when the value is the same continuously for a predetermined time (or number of times). Since the command signal P3 is changed, it is possible to prevent malfunctions caused by accidentally touching a switch or generating electrical noise. Further, according to the present invention, malfunctions can be prevented by the built-in microcomputer's own calculations, so the structure is simplified and reliability is improved without increasing costs. In addition, the preset value
N ₁ and N ₂ can be made equal, and the sampling pulse can also be supplied externally. The present invention is of course applicable to general control devices, but is particularly applicable to numeric keyswitches for setting the number of sheets of copying machines, micro switches for counting the number of sheets,
It is convenient to apply to a switch for setting and clearing the number of sheets.

[Brief explanation of the drawing]

Figure 1 shows one example of a malfunction prevention device for a conventional control device.
A block diagram showing an example, FIG. 2 is a schematic diagram of essential parts of an embodiment of the method of the present invention, FIG. 3 is a flowchart showing the operation of an embodiment of the method of the present invention, and FIG. 4 is a timing chart thereof. FIG. 5 is a functional block diagram of the present invention. 1...Microcomputer, 2...Switch, 3
...Operation command output terminal, 4...Sampling signal output terminal, 5...Input terminal.

Claims (1)

[Scope of Claims] 1. A control incorporating a microcomputer that receives as input a signal representing the open/closed state of a switch that commands the operation of a machine, and generates an operation command signal that controls the operation of the machine in response to the signal input. A device for preventing malfunction of the device, which includes a sampling pulse generating means for generating sampling pulses at scheduled time intervals, and 2 representing the open/closed state of the operation command switch.
an open/close state detection means that generates a value signal; an AND circuit that calculates the AND of the sampling pulse and the binary signal; and an exclusive OR circuit that calculates the exclusive OR of the AND and the operation command signal. a counter that counts the output of the exclusive OR circuit and is cleared by an inverted signal of the output; a count value of the counter is compared with a preset reference value; A malfunction prevention device for a control device, comprising: a comparator that generates an output when a numerical value is equal to or greater than a reference value; and means for inverting the operation command signal in response to the output of the comparator. 2. The malfunction prevention device for a control device according to claim 1, wherein the reference value is switched in accordance with an operation command signal being generated at the time.