Hydraulic Lock-Based Braking Speed Control Apparatus for a Grinding Machine

Abstract

The present invention relates to a grinding machine braking device, and more specifically, to a hydraulic lock-based braking speed control device for a grinding machine that can quickly and safely stop a rotary table of a grinding machine driven by a hydraulic motor.

Description

Technology Field

[0001] The present invention relates to a grinding machine braking device, and more specifically, to a hydraulic lock-based braking speed control device for a grinding machine that can quickly and safely stop a rotary table of a grinding machine driven by a hydraulic motor. Background Technology

[0002] Generally, a grinder is a device that places a workpiece on a rotary table and rotates it while reciprocating a grinding member over the workpiece to grind the surface of the workpiece flat to a desired thickness.

[0003] As illustrated in FIG. 1, a conventional grinder (1) is composed of a rotary table (10) on which a workpiece (S) is placed, and a rotary grinding member (20) that grinds the surface of the workpiece (S) while moving back and forth toward the workpiece (S).

[0004] And, the rotary table (10) is typically driven by a hydraulic motor (30), and a large amount of cooling fluid is supplied through a nozzle (40) to cool the frictional heat generated during the grinding operation.

[0005] Accordingly, when the operator presses the stop button, the hydraulic fluid supply path (50) among the hydraulic fluid supply path (50) and hydraulic fluid discharge path (60) connected to the hydraulic motor (30) is closed so that the supply of hydraulic fluid is cut off, and accordingly, the output shaft (31) of the hydraulic motor (30) does not rotate, and the rotating table (10) rotating along the output shaft (31) gradually stops and braking is achieved.

[0006] However, the braking method of this conventional grinder (1) has a problem in that the idle rotation due to the inertia of the rotary table (10) continues for a considerable amount of time, and the waiting time for the next operation becomes long, which significantly reduces productivity.

[0007] At this time, one might consider installing a conventional friction-type braking device to quickly stop the rotary table (10), but due to the nature of the grinding operation, a large amount of cooling oil is supplied to the rotary table (10), and since this cooling oil significantly reduces the friction coefficient between the friction brake pad and the rotary table (10), thereby lowering braking efficiency, it is technically very difficult to secure stable braking power.

[0008] In addition, conventional braking methods cannot variably adjust the stopping time of the rotary table (10) according to working conditions, so there is a problem in that the equipment lifespan is shortened as excessive mechanical shock is applied to the rotary table (10), hydraulic motor (30), and related parts due to sudden stopping. The problem to be solved

[0009] The present invention was devised to solve the aforementioned problems and aims to provide a hydraulic lock-based braking speed control device for a grinder that can quickly and safely stop a rotary table in an environment where a large amount of cooling oil is supplied, and can minimize the impact applied to the rotary table and related parts by variably setting the braking speed according to working conditions.

[0010] The problems of the present invention are not limited to those mentioned above, and other unmentioned problems will be clearly understood by those skilled in the art from the description below. means of solving the problem

[0011] The present invention is intended to solve the above-mentioned problems. The hydraulic lock-based braking speed control device of the present invention comprises, in a grinding machine equipped with a hydraulic motor that rotates a rotary table on which a workpiece is placed, a supply shut-off valve installed in a hydraulic fluid supply path that supplies hydraulic fluid to the hydraulic motor, which blocks the supply of the hydraulic fluid upon input of a braking signal and permits the supply of the hydraulic fluid upon input of an operation signal, and a discharge shut-off valve installed in a hydraulic fluid discharge path through which hydraulic fluid discharged from the hydraulic motor is discharged, which blocks the discharge of the hydraulic fluid upon input of a braking signal and permits the discharge of the hydraulic fluid upon input of an operation signal; wherein, by operation according to the braking signal of the supply shut-off valve and the discharge shut-off valve, the hydraulic motor is switched to a hydraulic lock state in which the hydraulic fluid is neither supplied nor discharged, and the hydraulic fluid trapped inside the hydraulic motor in the hydraulic lock state acts as a resistor to brake the rotary table.

[0012] In addition, the discharge shut-off valve may be a pneumatically driven valve that is opened and closed by compressed air.

[0013] In this case, the discharge shut-off valve may be a normally open valve that remains open when compressed air is not supplied.

[0014] In addition, the above discharge shut-off valve may be an air ball valve.

[0015] Meanwhile, the present invention may further include a control valve that continuously adjusts the closing speed of the discharge shut-off valve by controlling the flow rate or pressure of compressed air supplied to the discharge shut-off valve, thereby variably setting the braking time of the rotary table.

[0016] In this case, the control valve may be a solenoid valve operated by an electrical signal.

[0017] In addition, the solenoid valve is driven by voltage, current, or pulse width modulation to change the average flow rate of compressed air supplied to the discharge shut-off valve, thereby controlling the closing time of the discharge shut-off valve to correspond to a target braking time set by the user.

[0018] In addition, the solenoid valve may be provided with a discharge port for discharging compressed air supplied to the discharge shut-off valve to the outside.

[0019] In addition, the control valve can be controlled to rapidly brake the rotary table by bypassing the speed control function that limits the flow rate of compressed air supplied to the discharge shut-off valve upon input of an emergency stop signal, and by immediately fully opening the compressed air supply path to the discharge shut-off valve so that the discharge shut-off valve closes at the maximum possible speed.

[0020] Meanwhile, it may further include a control device for controlling the operation of the supply shut-off valve and the discharge shut-off valve, a brake button operated by an operator to command the stop of the rotary table and input a braking signal to the control device, an operation button operated by an operator to command the operation of the rotary table and input an operation signal to the control device, and an emergency stop button operated by an operator in an emergency situation to input an emergency stop signal to the control device. Effects of the invention

[0021] As described above, the hydraulic lock-based braking speed control device for a grinder according to the present invention is configured such that the supply shut-off valve and the discharge shut-off valve operate simultaneously to switch the hydraulic motor to a hydraulic lock state. Therefore, compared to a friction method that relies on the friction coefficient, the rotary table can be stopped stably and quickly even in an environment where a large amount of cooling fluid is supplied, thereby significantly reducing work waiting time and improving productivity.

[0022] In addition, since the present invention continuously controls the flow rate or pressure of compressed air supplied to the discharge shut-off valve using a control valve, the closing speed of the discharge shut-off valve can be variably set according to operating conditions, allowing the user to adjust the braking time of the rotary table as desired. This has the effect of minimizing mechanical shock applied to the rotary table, hydraulic motor, and related parts, and extending the lifespan of the equipment.

[0023] In addition, since the solenoid valve of the present invention is driven by voltage, current, or pulse width modulation, the average flow rate of compressed air is electronically and precisely controlled, thereby enabling smooth braking that accurately corresponds to the target braking time.

[0024] In addition, since the present invention is configured to close the discharge shut-off valve at maximum speed by bypassing the speed control function upon input of an emergency stop signal, it has the effect of ensuring the safety of workers and equipment by immediately and rapidly braking the rotary table in emergency situations.

[0025] The effects of the present invention are not limited to those mentioned above, and other unmentioned effects will be clearly understood by a person skilled in the art from the description below. Brief explanation of the drawing

[0026] FIG. 1 is a schematic diagram showing the configuration of a conventional grinder. FIG. 2 is a diagram schematically showing the configuration of a hydraulic lock-based braking speed control device for a grinder according to the present invention. FIG. 3 is a perspective view of a hydraulic lock-based braking speed control device for a grinder according to the present invention. FIG. 4 is a block diagram showing the configuration of a control device constituting the present invention. Specific details for implementing the invention

[0027] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. The advantages and features of the present invention and the methods for achieving them will become clear by referring to the embodiments described below in detail together with the attached drawings. However, the present invention is not limited to the embodiments disclosed below but can be implemented in various different forms. These embodiments are provided merely to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the invention, and the present invention is defined only by the scope of the claims. Throughout the specification, the same reference numerals refer to the same components.

[0028] Unless otherwise defined, all terms used herein (including technical and scientific terms) may be used in a meaning commonly understood by those skilled in the art to which the present invention pertains. Furthermore, terms defined in commonly used dictionaries are not to be interpreted ideally or excessively unless explicitly and specifically defined otherwise. The terms used herein are for describing embodiments and are not intended to limit the present invention. In this specification, the singular form includes the plural form unless specifically stated otherwise in the text.

[0029] As used in the specification, "comprises" and / or "comprising" do not exclude the presence or addition of one or more other components, steps, actions, and / or elements to the mentioned components, steps, actions, and / or elements.

[0030] As illustrated in FIGS. 2 to 4, the hydraulic lock-based braking speed control device (100) of a grinder according to the present invention comprises a supply shut-off valve (110), a discharge shut-off valve (120), an air supply passage (130), a control valve (140), and a control device (160).

[0031] The above supply shut-off valve (110) is installed in a hydraulic fluid supply path (50) that supplies hydraulic fluid from a hydraulic pump (not shown) to a hydraulic motor (30) that rotates a rotary table (10) on which a workpiece (S) is placed, and controls the supply of hydraulic fluid. Specifically, the above supply shut-off valve (110) opens the hydraulic fluid supply path (50) to supply hydraulic fluid to the hydraulic motor (30) when an operation signal is input, and closes the hydraulic fluid supply path (50) to immediately cut off the supply of hydraulic fluid to the hydraulic motor (30) when a braking signal is input.

[0032] The above supply shut-off valve (110) is preferably configured as a solenoid direct-acting valve driven directly by an electric signal. The solenoid direct-acting valve operates by moving a plunger to directly open and close the fluid path when the solenoid coil inside the valve is energized by an electric signal output from a control device (160). This solenoid direct-acting valve has the advantage of enabling immediate opening and closing operations using only an electric signal without a separate driving source such as compressed air, thereby minimizing the response delay from the input of a braking signal to the shut-off of the hydraulic fluid supply.

[0033] In this case, it is preferable that the supply shut-off valve (110) be configured as a normally closed valve that maintains a closed state when no electrical signal is applied. The normally closed valve has a fail-safe characteristic that prevents the rotary table (10) from continuing to operate unnecessarily even when there is a malfunction of the control device (160) or power cutoff, because it automatically returns to a closed state by the restoring force of a spring in abnormal situations where the power supply is interrupted, thereby cutting off the supply of hydraulic fluid to the hydraulic motor (30). In this way, the supply shut-off valve (110) is configured to be normally closed and the discharge shut-off valve (120) is configured to be normally open. When an abnormal situation occurs, the supply shut-off valve (110) automatically cuts off the supply of hydraulic fluid, while the discharge shut-off valve (120) automatically opens the hydraulic fluid discharge path (60). This allows the hydraulic motor (30) to be switched to a state where it can rotate freely without being trapped in a hydraulic lock state, thereby greatly improving the safety of the entire device. The discharge shut-off valve (120) is installed in the hydraulic fluid discharge path (60) through which the hydraulic fluid used by the hydraulic motor (30) is discharged, and controls the discharge of the hydraulic fluid. When an operation signal is input, the discharge shut-off valve (120) opens the hydraulic fluid discharge path (60) to allow the hydraulic fluid to be discharged smoothly into the hydraulic fluid storage tank (not shown), and when a braking signal is input, it closes the hydraulic fluid discharge path (60) to block the discharge of the hydraulic fluid.

[0034] In this way, when a braking signal is input, the supply shut-off valve (110) closes the hydraulic fluid supply path (50) and at the same time the discharge shut-off valve (120) closes the hydraulic fluid discharge path (60), the hydraulic motor (30) switches to a hydraulic lock state in which no hydraulic fluid is supplied or discharged.

[0035] In the above hydraulic lock state, the hydraulic fluid trapped inside the hydraulic motor (30) acts as a resistor to quickly brake the rotation of the rotary table (10). Since this hydraulic lock braking method provides stable braking force regardless of the presence of cooling fluid, it exhibits significantly superior braking performance compared to the friction method in a grinding machine environment where a large amount of cooling fluid is supplied.

[0037] Meanwhile, in the above hydraulic lock state, the hydraulic motor (30) may temporarily increase its internal hydraulic pressure as the force to rotate it by means of the inertia of the rotary table (10) is transmitted as pressure to the internal hydraulic fluid. Since this over-pressure may cause damage to the hydraulic motor (30) and related hydraulic components if it exceeds the allowable pressure, the present invention is preferably provided with a relief valve (200) on the hydraulic fluid discharge path (60) between the hydraulic motor (30) and the discharge shut-off valve (120).

[0038] The above relief valve (200) automatically opens when the hydraulic pressure in the hydraulic fluid discharge path (60) exceeds a preset allowable pressure (set pressure), thereby diverting the excess pressure hydraulic fluid to the hydraulic fluid storage tank side and maintaining the internal pressure of the hydraulic motor (30) below the set pressure. The set pressure of the above relief valve (200) is set to be below the rated allowable pressure of the hydraulic motor (30) and is appropriately determined by considering the maximum hydraulic pressure that may occur during braking according to the weight of the rotary table (10) and the maximum rotational speed.

[0039] In addition, since the relief valve (200) returns to a closed state immediately after the overpressure is relieved in the hydraulic locking state, the braking force caused by the hydraulic locking is maintained. As such, by providing the relief valve (200) on the hydraulic fluid discharge path (60), the hydraulic motor (30) and related parts are protected from overpressure even in situations where an excessive inertial load is applied, thereby improving the durability and reliability of the device.

[0041] The above discharge shut-off valve (120) is preferably composed of a pneumatically driven valve that is opened and closed by compressed air.

[0042] Compared to a solenoid direct-acting valve in which an electric signal acts directly, the above-mentioned pneumatic actuated valve has the advantage of greater driving force and higher sealing reliability, as well as stable operation even in environments where dust and cooling oil generated during grinding operations are scattered.

[0043] In this case, it is preferable that the discharge shut-off valve (120) be configured as a normally open valve that remains open when compressed air is not supplied.

[0044] The normally open valve automatically returns to an open state by the elastic force of the built-in return spring when the compressed air supply is interrupted, so even in abnormal situations where the electrical or pneumatic supply is cut off, the hydraulic fluid discharge path (60) remains open, thereby having a fail-safe characteristic that ensures the free rotation of the hydraulic motor (30).

[0045] In addition, the discharge shut-off valve (120) may be configured as an air ball valve. The air ball valve opens and closes the flow path by rotating a spherical ball, thereby maximizing the cross-sectional area of ​​the flow path when fully open to minimize the discharge resistance of the hydraulic fluid, and when fully closed, almost no leakage of the hydraulic fluid occurs, thereby ensuring a secure hydraulic lock state.

[0046] The above-mentioned discharge shut-off valve (120) maintains an open state by the elastic force of the return spring when compressed air is not supplied, allowing the hydraulic fluid discharged from the hydraulic motor (30) to flow freely, and when compressed air is supplied through the air supply path (130), the air pressure overcomes the elastic force of the return spring and closes the hydraulic fluid discharge path (60), thereby blocking the discharge of the hydraulic fluid.

[0047] The above control valve (140) is installed in an air supply path (130) that supplies compressed air to a discharge shut-off valve (120), and by controlling the flow rate or pressure of the compressed air supplied through the air supply path (130), the closing speed of the discharge shut-off valve (120) is continuously adjusted to variably set the braking time of the rotary table (10).

[0048] Preferably, the control valve (140) is composed of a solenoid valve that operates by an electrical signal. In this case, the control valve (140) may be driven by voltage, current, or pulse width modulation (PWM) to change the average flow rate of compressed air supplied to the discharge shut-off valve (120). When using pulse width modulation, the duty ratio of the electrical signal supplied to the solenoid coil is adjusted to precisely control the average air flow rate, thereby allowing the closing time of the discharge shut-off valve (120) to accurately correspond to the target braking time set by the user.

[0049] In this way, by reducing the closing speed of the discharge shut-off valve (120) through the control valve (140), the closing of the hydraulic fluid discharge path (60) is gradually achieved, thereby preventing sudden changes in hydraulic pressure, and as a result, smooth and safe braking is achieved without impacting the related parts.

[0050] In addition, the control valve (140) is provided with a discharge port (150) for discharging compressed air supplied to the discharge shut-off valve (120) to the outside. When the rotary table (10) is reactivated, if the control valve (140) closes the air supply passage (130), the supply of compressed air is stopped, and at the same time, the compressed air supplied inside the discharge shut-off valve (120) is quickly discharged to the outside through the discharge port (150), thereby releasing the air pressure applied to the discharge shut-off valve (120). Accordingly, the discharge shut-off valve (120) returns to its original position by the elastic force of the return spring, thereby quickly opening the operating fluid discharge passage (60).

[0051] Meanwhile, the present invention may further include a control device (160), a braking button (170), an operation button (180), and an emergency stop button (190).

[0052] The above control device (160) is a controller that electrically controls the operation of the supply shut-off valve (110) and the control valve (140), and receives signals from the brake button (170), the operation button (180), and the emergency stop button (190) and outputs open / close commands to each valve.

[0053] The above braking button (170) is an input device operated by an operator to command the stopping of the rotary table (10), and is connected to a control device (160) to generate a braking signal.

[0054] The above-mentioned operating button (180) is an input device operated by a worker to command the operation of the rotary table (10), and is connected to a control device (160) to generate an operation signal.

[0055] The above emergency stop button (190) is an input device that inputs an emergency stop signal to the control device (160) by being operated by a worker in an emergency situation.

[0056] The operation process of the hydraulic lock-based braking speed control device (100) of the grinder according to the present invention configured as described above is as follows.

[0057] When the operator presses the operation button (180), the control device (160) receives the operation signal and outputs an opening signal to the supply shut-off valve (110) and simultaneously outputs a closing signal to the control valve (140). Accordingly, the supply shut-off valve (110) opens the hydraulic fluid supply path (50) so that hydraulic fluid is supplied from the hydraulic pump to the hydraulic motor (30), and the hydraulic motor (30) is driven so that the rotary table (10) rotates and grinding of the workpiece (S) is performed.

[0058] At the same time, the control valve (140) closes the air supply path (130) so that compressed air is not supplied to the discharge shut-off valve (120), and the discharge shut-off valve (120) is maintained in an open state by the elastic force of the return spring, so the hydraulic fluid used in the hydraulic motor (30) is smoothly discharged through the hydraulic fluid discharge path (60).

[0059] When the operator presses the brake button (170), the control device (160) receives the brake signal and outputs a closing signal to the supply shut-off valve (110) and simultaneously outputs an opening signal to the control valve (140). Accordingly, the supply shut-off valve (110) closes the hydraulic fluid supply path (50), so that the supply of hydraulic fluid to the hydraulic motor (30) is immediately stopped, and the control valve (140) opens the air supply path (130) so that compressed air is supplied to the discharge shut-off valve (120).

[0060] Since the flow rate or pressure of the compressed air flowing in through the air supply channel (130) is controlled by the control valve (140), the discharge shut-off valve (120) is gradually closed at a speed corresponding to the target braking time set by the user. When the discharge shut-off valve (120) is completely closed, the hydraulic motor (30) is in a hydraulic lock state, and the hydraulic fluid trapped inside acts as a resistor, causing the rotary table (10) to stop.

[0061] Meanwhile, when the emergency stop button (190) is operated, the control device (160) receives the emergency stop signal and immediately closes the supply shut-off valve (110), while simultaneously bypassing the speed control function of the control valve (140) to fully open the air supply path (130). Accordingly, compressed air is supplied to the discharge shut-off valve (120) at the maximum flow rate, and the discharge shut-off valve (120) closes at the maximum possible speed, thereby rapidly braking the rotary table (10).

[0062] When the operating button (180) is pressed to resume the next operation after the rotary table (10) has stopped, the control device (160) outputs a closing signal to the control valve (140), thereby closing the air supply path (130). Accordingly, the supply of compressed air is stopped, and at the same time, the compressed air supplied inside the discharge shut-off valve (120) is rapidly discharged to the outside through the discharge port (150), causing the discharge shut-off valve (120) to open due to the elastic force of the return spring, thereby opening the hydraulic fluid discharge path (60). At the same time, the control device (160) outputs an opening signal to the supply shut-off valve (110), thereby opening the hydraulic fluid supply path (50), and as hydraulic fluid is supplied to the hydraulic motor (30), the rotary table (10) rotates again.

[0063] Meanwhile, although not illustrated, the hydraulic lock-based braking speed control device (100) of the grinder according to the present invention may additionally be equipped with a manual operating lever that can manually operate the discharge shut-off valve (120). Accordingly, even if the power supply is interrupted or a malfunction occurs in the control device (160), the operator can manually stop the rotary table (10), thereby further improving the safety and reliability of the device.

[0064] Additionally, although not illustrated, the hydraulic lock-based braking speed control device (100) of the grinder according to the present invention may additionally be equipped with a rotation detection sensor (not illustrated) that detects whether the rotary table (10) is rotating or its rotation speed in order to implement an automatic braking time correction function. The rotation detection sensor is installed adjacent to the lower part of the rotary table (10) or the output shaft of the hydraulic motor (30) and may be composed of a Hall sensor, an optical encoder, or a proximity sensor.

[0065] In this case, the control device (160) measures the time from the point of input of the braking signal until the point of detection of the rotation of the rotating table (10) by the rotation detection sensor as the actual braking time, and calculates the deviation by comparing the actual braking time with the target braking time set by the user. Based on the calculated deviation, the control device (160) performs closed-loop control to converge the braking time to the target braking time by automatically correcting the duty ratio of the pulse width modulation (PWM) signal output to the control valve (140) during the next braking. Specifically, if the actual braking time is longer than the target braking time, the duty ratio is increased during the next braking to increase the average flow rate of compressed air supplied to the discharge shut-off valve (120) and speed up the closing speed, and if the actual braking time is shorter than the target braking time, the duty ratio is lowered to slow down the closing speed. With this automatic correction function, the braking time is always accurately maintained at the target braking time regardless of environmental changes such as changes in viscosity due to temperature changes of the working fluid, fluctuations in compressed air supply pressure, and wear of the discharge shut-off valve (120), so the reproducibility and stability of the process are greatly improved.

[0066] Additionally, although not illustrated, the hydraulic lock-based braking speed control device (100) of the grinder according to the present invention can implement a multi-step braking mode. In the multi-step braking mode, instead of closing the discharge shut-off valve (120) at a single speed after inputting a braking signal, the control device (160) drives the control valve (140) to apply different closing speeds to each section by dividing the braking process into multiple sections.

[0067] Specifically, the control device (160) sets the duty cycle of the control valve (140) low during the initial braking phase to gradually close the discharge shut-off valve (120) at a slow speed, thereby gradually reducing the opening of the hydraulic fluid discharge path (60). In this initial phase, the discharge resistance gradually increases while the discharge of hydraulic fluid is not completely blocked, so a gradual braking force is applied to the rotary table (10), and the inertial energy is absorbed smoothly without sudden hydraulic shock. Subsequently, in the later phase where the rotational speed of the rotary table (10) decreases below a preset reference speed, the control device (160) increases the duty cycle to rapidly and completely close the discharge shut-off valve (120), thereby rapidly exhausting the remaining inertial energy and finally stopping the rotary table (10). The reference speed may be preset in the control device (160) or dynamically determined based on rotational speed information acquired in real time from a rotation detection sensor.

[0068] According to this multi-stage braking mode, the total braking time can be shortened while suppressing the sudden hydraulic surge at the beginning of braking, thereby minimizing mechanical shock to the hydraulic motor (30) and related parts, and improving productivity. In particular, when the multi-stage braking mode is applied together with the aforementioned automatic braking time correction function, the switching point for each section and the duty ratio of each section can be automatically optimized based on historical data of the actual braking time, thereby enabling more precise and stable braking control.

[0069] Although embodiments of the present invention have been described above with reference to the attached drawings, those skilled in the art will understand that the present invention may be implemented in other specific forms without changing its technical concept or essential features. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. Explanation of the symbols

[0070] 10: Rotating table 30: Hydraulic motor 50: Operating fluid supply path 60: Operating fluid discharge path 100: Hydraulic lock-based braking speed control device for a grinder 110: Supply shut-off valve 120: Discharge shut-off valve 130: Air supply Euro 140: Control valve 150: Discharge port 160: Control unit 170: Brake button 180: Operation button 190: Emergency Stop Button S: Workpiece

Claims

Claim 1 A hydraulic lock-based braking speed control device for a grinding machine equipped with a hydraulic motor that rotates a rotary table on which a workpiece is placed, comprising: a supply shut-off valve installed in a hydraulic fluid supply path that supplies hydraulic fluid to the hydraulic motor, which blocks the supply of the hydraulic fluid upon input of a braking signal and permits the supply of the hydraulic fluid upon input of an operation signal; and a discharge shut-off valve installed in a hydraulic fluid discharge path through which hydraulic fluid discharged from the hydraulic motor is discharged, which blocks the discharge of the hydraulic fluid upon input of a braking signal and permits the discharge of the hydraulic fluid upon input of an operation signal, wherein the hydraulic motor is switched to a hydraulic lock state in which the hydraulic fluid is neither supplied nor discharged by the operation of the supply shut-off valve and the discharge shut-off valve according to the braking signal, and the hydraulic fluid trapped inside the hydraulic motor in the hydraulic lock state acts as a resistor to brake the rotary table, and further comprising controlling the operating speed of the discharge shut-off valve to adjust the braking speed of the hydraulic motor. Claim 2 A hydraulic lock-based braking speed control device for a grinder, characterized in that, in claim 1, the discharge shut-off valve is a pneumatically driven valve that is opened and closed by compressed air. Claim 3 A hydraulic lock-based braking speed control device for a grinder, characterized in that, in paragraph 2, the discharge shut-off valve is a normally open valve that maintains an open state when compressed air is not supplied. Claim 4 A hydraulic lock-based braking speed control device for a grinder, characterized in that, in paragraph 3, the discharge shut-off valve is an air ball valve. Claim 5 delete Claim 6 A hydraulic lock-based braking speed control device for a grinder, further comprising, in any one of claims 2 to 4, a control valve that continuously adjusts the closing speed of the discharge shut-off valve by controlling the flow rate or pressure of compressed air supplied to the discharge shut-off valve to variably set the braking time of the rotary table. Claim 7 A hydraulic lock-based braking speed control device for a grinder, characterized in that, in claim 6, the control valve is a solenoid valve operated by an electric signal. Claim 8 A hydraulic lock-based braking speed control device for a grinder, characterized in that, in claim 7, the solenoid valve is driven by a voltage, current, or pulse width modulation method to change the average flow rate of compressed air supplied to the discharge shut-off valve, thereby controlling the closing time of the discharge shut-off valve to correspond to a target braking time set by the user. Claim 9 In claim 7, the above solenoid valve is a hydraulic lock-based braking speed control device for a grinder having a discharge port for discharging compressed air supplied to the discharge shut-off valve to the outside. Claim 10 A hydraulic lock-based braking speed control device for a grinder, wherein the control valve is controlled to rapidly brake a rotary table by bypassing a speed control function that limits the flow rate of compressed air supplied to the discharge shut-off valve upon input of an emergency stop signal, and by immediately fully opening the compressed air supply path to the discharge shut-off valve so that the discharge shut-off valve is closed at the maximum possible speed. Claim 11 A hydraulic lock-based braking speed control device for a grinder according to claim 1, further comprising: a control device for controlling the operation of the supply shut-off valve and the discharge shut-off valve; a braking button operated by an operator to command the stopping of the rotary table and inputting a braking signal to the control device; an operating button operated by an operator to command the operation of the rotary table and inputting an operating signal to the control device; and an emergency stop button operated by an operator in an emergency situation to input an emergency stop signal to the control device.

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