JP2845241B2 - Air puff tonometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention operates a piston driving means by an electric current supplied from a power supply to compress air in a cylinder,
The present invention relates to an air-puff tonometer for ejecting compressed air from a nozzle toward an eye to be examined. (Prior Art) Conventionally, an air puff type tonometer of this type is known, for example, as shown in FIG. In this device, an arm 2 of a rotary solenoid 1 (piston driving means) is connected to a piston rod 4 integrated with a piston 3, and a compression chamber 6 of a cylinder 5 provided with the piston 3 is directed to an eye (not shown). It communicates with a nozzle (not shown). And the rotary solenoid 1
When the power is supplied, the arm 2 rotates counterclockwise, and when the power is stopped, the arm 2 returns to the current state by the spring force of a spring (not shown). In such a configuration, when the rotary solenoid 1 is operated to rotate the arm 2 in the counterclockwise direction, the piston 3 is displaced upward via the piston rod 4, whereby the air in the compression chamber 6 is compressed. Then, it is sprayed from the nozzle onto the eye to be examined. By the way, when blowing compressed air from the nozzle, that is, when generating air puff, the piston 3
Therefore, a large current flows through the rotary solenoid 1 via the constant current circuit 9. This large current is generated by storing charge in the capacitor 8 by the capacitor charging circuit 7 and releasing the stored charge in a short time. The constant current circuit 9 converts the large current to a constant current and supplies the constant current to the rotary solenoid 1. The constant current circuit 9 operates the rotary solenoid 1 so that the piston 3 compresses air with a predetermined force to make the pressure of the air puff constant. ing. (Problems to be Solved by the Invention) However, in the air puff type tonometer, a constant current is supplied to the rotary solenoid 1 by the constant current circuit 9 so that the piston 3 compresses air with a predetermined force. Therefore, if the gap between the piston 3 and the cylinder 5 changes due to wear or the like, the pressure of the compressed air in the cylinder 5 changes. Therefore, since the pressure of the air puff ejected from the nozzle also changes, particularly in the case of a tonometer that measures the time from the occurrence of an air puff to the time when the cornea applanates and determines the intraocular pressure from this measurement time, There is a problem that the measurement error becomes very large. (Objects of the Invention) Therefore, the present invention has been made in view of the above problems, and always keeps the pressure of compressed air in a cylinder at a predetermined pressure even when the gap between the piston and the cylinder changes. It is an object of the present invention to provide an air puff tonometer capable of performing the above-mentioned measures (means for solving the problems). An air puff tonometer for ejecting the compressed air from a nozzle toward a subject's eye; a pressure detecting means for detecting a pressure in the cylinder; and a reference signal indicating a predetermined predetermined pressure change is output. A reference signal output unit for performing a comparison between the pressure signal output from the pressure unit and the reference signal, and a control unit for controlling the piston driving unit based on a difference signal between the two signals. Characterized in that was. (Operation) The pressure detecting means detects a pressure signal corresponding to the pressure in the cylinder, the reference signal output means outputs a reference signal indicating a predetermined change in pressure, and the control means outputs the pressure signal from the pressure means. Since the pressure signal and the reference signal are compared and the piston driving means is controlled based on the difference signal between the two signals, the pressure of the air compressed by the piston can always be kept at a predetermined pressure. (Embodiment) Hereinafter, an embodiment of an air puff tonometer according to the present invention will be described with reference to the drawings. The same components as those shown in FIG. 3 are denoted by the same reference numerals, and the description thereof will be omitted. FIG. 1 is a block diagram showing a control system of an air puff tonometer. In the drawing, reference numeral 11 denotes a pressure for detecting a pressure in a compression chamber 6 of a cylinder 5 and outputting a voltage (pressure signal) corresponding to the detected pressure. A detecting device (pressure detecting means), which is constituted by, for example, a strain gauge type pressure detector. An error amplifier circuit 12 amplifies a difference between the voltage of the pressure signal output from the pressure detection device 11 and a reference wave voltage signal output from a reference wave voltage generation circuit (reference signal output means) 13 described later. It is composed of a differential amplifier circuit and the like. The reference wave voltage generation circuit 13 outputs a reference wave voltage signal having the same waveform as the pressure signal output by the pressure detection device 11 when the pressure in the compression chamber 6 of the cylinder 5 in the compression stroke changes ideally. In consideration of the delay time T with respect to the feedback control of the entire apparatus, the time point t _{0 is} advanced by the time T from the time point t ₁ at which the piston 3 starts to rise.
Output a reference wave voltage signal from the
(See (A) in the figure.) Numeral 14 designates a rotary solenoid 1 from the capacitor 8 so that the error amplification signal output from the error amplification circuit 13 becomes zero.
This is a current control circuit for controlling the current supplied to the transistor, which is composed of, for example, a power transistor, and controls the current flowing through the collector by inputting the error amplification signal to the base of the transistor. The error amplifier 12, the reference wave voltage generator 13, and the current controller 14 constitute a current controller. Next, the operation of the air-puff tonometer of the above embodiment will be described. Now, when the compression chamber 6 of the cylinder 5 is not compressed, that is, when the piston 3 is at the position shown in the drawing,
Capacitor 8 is charged by the capacitor-charging circuit 7, a reference wave voltage generation circuit 13 as shown in of FIG. 2 (A), and outputs the linear reference wave voltage signal Vt from time t _0. On the other hand, since the pressure signal Vp output from the pressure detection device 11 is zero, the error signal Vg output from the error amplification circuit 12 is
Becomes a voltage proportional to the reference wave voltage signal Vt and is input to the current control circuit 14, and the current control circuit 14
The discharge current from is supplied to the rotary solenoid 1. This current starts to flow through the rotary solenoid 1 and the time T
(Delay time) rotary solenoid from the time t ₁ after a lapse of 1
Is activated and the piston 3 rises, and the pressure detecting device 11
Output a pressure signal Vp proportional to the pressure in the compression chamber 6 as shown in FIG. Then, an error signal Vg error amplification circuit 12 in accordance with the difference between the pressure signal Vp and the reference wave voltage signal Vt to output time point t ₁ after as shown in the FIG. 2 (C), the error signal Vg is zero The current control circuit 14 supplies a current proportional to the voltage of the error signal Vg to the rotary solenoid 1 as shown in FIG. That is, the current is supplied to the rotary solenoid 1 so that the pressure signal Vp output from the pressure detecting device 11 matches the reference wave voltage signal Vt shown in FIG. Therefore, since the piston 3 compresses the air in the compression chamber 6 of the cylinder 5 so as to approach the ideal pressure, an air puff having a predetermined pressure can be obtained. By the way, the pressure signal Vp output from the pressure detecting device 11 as the gap between the cylinder 5 and the piston 3 changes due to wear or the like and the pressure in the compression chamber 6 decreases as shown by the broken line in FIG. , The difference between the pressure signal Vp and the reference wave voltage signal Vt output from the reference wave voltage generation circuit 13 increases, and the voltage of the error signal Vg output from the error amplification circuit 12 increases. As a result, the current control circuit 14 increases the current supplied to the rotary solenoid 1, so that the piston 3 rises with a stronger force, whereby the air in the compression chamber 6 reaches a predetermined pressure. On the other hand, when the pressure signal Vp and the reference wave voltage generation circuit 13
And the difference from the reference wave voltage signal Vt output from
The voltage of the error signal Vg output from the error amplifying circuit 12 decreases, whereby the current control circuit 14
, The piston 3 rises with a lower force, which brings the air in the compression chamber 6 to a predetermined pressure. As described above, when the gap between the cylinder 5 and the piston 3 changes due to wear or the like and the pressure in the compression chamber 6 is about to change, the current control circuit 14 controls the current supplied to the rotary solenoid 1 to , The air in the compression chamber 6 can always be compressed to a predetermined pressure. In the above embodiment, the case where the gap between the cylinder 5 and the piston 3 is changed due to abrasion or the like is described. However, the same effect can be obtained when the rotary solenoid 1 is deteriorated and the pressure in the compression chamber 6 is changed. Can be obtained. Further, if the present invention is applied to an air puff tonometer of a type that measures the pressure in the cylinder 5 to estimate the pressure of the air puff at the position of the eye to be measured and measures the intraocular pressure based on the estimated pressure, A measurement can be made. Furthermore, if the error amplifier circuit 13 has P, I, D (comparison, integration, and differentiation) characteristics, the pressure change in the compression chamber 6 during the compression stroke can be made closer to the ideal pressure change. If an error function is added to the error amplification circuit 13 so that an alarm is issued when the difference between the ideal pressure and the actual pressure of the compression chamber 6 becomes larger than a predetermined value, the alarm is supplied to the rotary solenoid 1. It is possible to notify the measurer of an abnormality such as the current or the inside of the cylinder 5. Further, the case where the piston 3 is driven by a force proportional to the current has been described. However, the present invention is not limited to this, and it is needless to say that the piston 3 can be applied to a device driven by a force proportional to a voltage. (Effects of the Invention) As described above, the present invention is configured as described above. Therefore, even if the clearance between the cylinder and the piston changes due to wear or the piston driving means deteriorates. This has the effect that the air in the cylinder can be constantly compressed to a predetermined pressure, and more accurate intraocular pressure can be measured.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a control system of an air puff tonometer according to an embodiment, and FIGS. 2 (A) to 2 (D) show signals output from respective circuits and pressures in a compression chamber. FIG. 3 is an explanatory diagram showing a schematic configuration of a conventional air-puff tonometer. 1 Rotary solenoid 5 Cylinder 11 Pressure detector 12 Error amplification circuit 13 Reference voltage generator 14 Current control circuit

Claims (1)

(57) [Claims] In an air puff tonometer for activating piston driving means to compress air in a cylinder and ejecting the compressed air from a nozzle toward an eye to be examined, a pressure detecting means for detecting a pressure in the cylinder; A reference signal output unit that outputs a reference signal indicating a set predetermined pressure change; a pressure signal output from the pressure unit and the reference signal; comparing the reference signal with the piston driving unit based on a difference signal between the two signals; An air puff-type tonometer characterized by comprising control means for controlling.