Protective apparatus for a machine tool

A protective apparatus and a machine tool are provided. The machine tool includes an operational element, a driving element, and the protective apparatus. The operational element and the driving element are disposed on machine table. The protective apparatus includes an insulating unit, conducting unit, capacitance sensor, and control unit. The insulating unit is disposed between the operational element and the driving element. The driving element drives the operational element by the insulating unit. The conducting unit contacts the operational element. The capacitance sensor electrically connects the conducting unit for sensing capacitance of the conducting unit. The control unit electrically connects the capacitance sensor and the driving element and determines whether a user approaches the operational element based on the capacitance. When the control unit detects that the distance between the user and the operational element is too close, the control unit stops the operation of the operational element.

BACKGROUND

1. Technical Field

The present disclosure relates to a protective apparatus for a machine tool, in particular, to a protective apparatus for a machine tool for preventing an operational element of the machine tool in operation from harming the user.

2. Description of Related Art

In cutting tools, the machine tool is one that easily can cut the user in operation, especially the machine tool for cutting wood. Either the professional technician or the do-it-yourself person easily gets hurt by using the machine tool. In order to increase the safety of using the machine tool, the traditional machine tool is configured with the protective apparatus.

Regarding the protective apparatus of the machine tool, one method is a clear shield installed around the machine tool to avoid the distance between the user and a saw blade configured in the machine tool getting too close. Another method is a security sensor installed around the machine tool to stop the operation of the machine tool when the distance between the user and the saw blade configured in the machine tool gets too close. However, the security sensor has many blind spots for sensing, causing safety problems for the user because of the sensing failure. Therefore, the protective method of installing the security sensor around the machine tool easily causes the industrial safety problem.

SUMMARY

The present disclosure provides a protective apparatus adapted for a machine tool. The machine tool includes a driving element and a saw blade, the driving element used for driving the saw blade. The protective apparatus includes an insulating unit, a conducting unit, a capacitance sensor and a control unit. The insulating unit is configured between the saw blade and the driving element, and the driving element driving the saw blade through the insulating unit. The conducting unit is in direct contact with the saw blade. The capacitance sensor is electrically connected to the conducting unit. The control unit is electrically connected to the capacitance sensor and the driving element. Before the saw blade is driven by the driving element, the protective apparatus operates in a correction mode, the control unit outputs a first prompting signal for prompting a user to place his or her hand in a front correction region located in front of saw teeth of the saw blade. The capacitance sensor obtains a reference capacitance. The capacitance sensor senses a first capacitance of the conducting unit that is generated when the user's hand is in the front correction region without contacting with the saw blade. The control unit calculates a capacitance threshold according to the reference capacitance and the first capacitance, the capacitance threshold is larger than the reference capacitance and smaller than the first capacitance. When the saw blade is driven by the driving element, the conducting unit maintains contact with the saw blade, the user moves his or her hand toward the saw teeth of the saw blade for cutting an object, the protective apparatus enters a protection mode, the capacitance sensor senses a practical capacitance of the conducting unit, the control unit compares the practical capacitance and the capacitance threshold. When the control unit determines that the practical capacitance is larger than the capacitance threshold, the control unit controls the driving element to stop driving the saw blade.

In addition, the present disclosure provides a machine tool includes a saw blade, a driving element and a protective apparatus. The saw blade is configured to a machine table. The driving element is configured to the machine table and used for driving the saw blade. The protective apparatus includes an insulating unit, a conducting unit, a capacitance sensor and a control unit. The insulating unit is configured between the saw blade and the driving element, and the driving element driving the saw blade through the insulating unit. The conducting unit is in direct contact with the saw blade. The capacitance sensor is electrically connected to the conducting unit. The control unit is electrically connected to the capacitance sensor and the driving element. Before the saw blade is driven by the driving element, the protective apparatus operates in a correction mode, the control unit outputs a first prompting signal for prompting a user to place his or her hand in a front correction region located in front of saw teeth of the saw blade. The capacitance sensor obtains a reference capacitance. The capacitance sensor senses a first capacitance of the conducting unit that is generated when the user's hand is in the front correction region without contacting with the saw blade. The control unit calculates a capacitance threshold according to the reference capacitance and the first capacitance. The capacitance threshold is larger than the reference capacitance and smaller than the first capacitance. When the saw blade is driven by the driving element, the conducting unit maintains contact with the saw blade, the user moves his or her hand toward the saw teeth of the saw blade for cutting an object, the protective apparatus enters a protection mode, the capacitance sensor senses a practical capacitance of the conducting unit, the control unit compares the practical capacitance and the capacitance threshold. When the control unit determines that the practical capacitance is larger than the capacitance threshold, the control unit controls the driving element to stop driving the saw blade.

In addition, the present disclosure provides a protective apparatus adapted for a machine tool. The machine tool includes a driving element and a saw blade, the driving element used for driving the saw blade. The protective apparatus includes an insulating unit, a conducting unit, a capacitance sensor and a control unit. The insulating unit is configured between the saw blade and the driving element, and the driving element driving the saw blade through the insulating unit. The conducting unit is in direct contact with the saw blade. The capacitance sensor is electrically connected to the conducting unit. The control unit is electrically connected to the capacitance sensor and the driving element. Before the saw blade is driven by the driving element and when a hand of the user is in contact with the saw blade, the capacitance sensor senses a reference capacitance of the conducting unit. Before the saw blade is driven by the driving element and when the hand of the user is not in contact with the saw blade, the protective apparatus operates in a correction mode, the control unit outputs a first prompting signal for prompting the user to place his or her hand in a front correction region located in front of saw teeth of the saw blade, the capacitance sensor obtains a reference capacitance and senses a first capacitance of the conducting unit that is generated when the user's hand is in the front correction region without contacting with the saw blade, the control unit calculates a capacitance threshold according to the reference capacitance and the first capacitance, the capacitance threshold being larger than the reference capacitance and smaller than the first capacitance. When the saw blade is driven by the driving element, the conducting unit maintains contact with the saw blade, the user moves his or her hand toward the saw teeth of the saw blade for cutting an object, the protective apparatus enters a protection mode, the capacitance sensor senses a practical capacitance of the conducting unit, the control unit compares the practical capacitance and the capacitance threshold. When the control unit determines that the practical capacitance is larger than the capacitance threshold, the control unit controls the driving element to stop driving the saw blade.

In addition, the present disclosure provides a protective method for controlling operation of a machine tool by using a protective apparatus. The protective apparatus includes an insulating unit, a conducting unit, a capacitance sensor and a control unit. The insulating unit is configured between the saw blade and the driving element. The conducting unit is in direct contact with the saw blade. The capacitance sensor is electrically connected to the conducting unit. The control unit is electrically connected to the capacitance sensor and the driving element. The machine tool includes a driving element and a saw blade used for driving the saw blade. The protective method includes the following steps: providing the protective apparatus that operates in a correction mode before the saw blade is driven by the driving element; outputting a first prompting signal for prompting a user to place his or her hand in a front correction region located in front of saw teeth of the saw blade by the control unit; obtaining a reference capacitance by the capacitance sensor; sensing a first capacitance of the conducting unit that is generated when the hand of the user is in the front correction region without contacting with the saw blade by the capacitance sensor; calculating a capacitance threshold according to the reference capacitance and the first capacitance by the control unit, wherein the capacitance threshold is larger than the reference capacitance and smaller than the first capacitance; controlling the driving element to drive the saw blade by the control unit while making the conducting unit be in direct contact with the saw blade; switching the protective apparatus to operate in a protection mode; sensing a practical capacitance of the conducting unit that is generated when the user moves his or her hand toward the saw teeth of the saw blade for cutting an object by the capacitance sensor; and determining whether or not the practical capacitance is larger than the capacitance threshold by the control unit, in response to determining that the practical capacitance is not larger than the capacitance threshold, continually controlling the driving element to drive the saw blade by the control unit, in response to determining that the practical capacitance is larger than the capacitance threshold, controlling the driving element to stop driving the saw blade.

To sum up, the exemplary embodiments of the present disclosure provide a protective apparatus and a machine tool, which can avoid that a capacitance sensor has blind spots for sensing, to enhance the security for the user using the machine tool.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

The present disclosure provides a protective apparatus and a machine tool. In the protective apparatus and the machine tool of the present disclosure, a conducting unit and an operational element are electrically connected with each other, so that a capacitance sensor can detect whether a user approaches the operational element. When the capacitance sensor detects that the distance between the user and the operational element is too close, the protective apparatus stops the operation of the operational element. Compared with the security sensor installed around the machine tool, the capacitance sensor of the present disclosure does not have the blind spot problem for sensing because the capacitance sensor electrically connects to the operational element through the conducting unit. Therefore, when the user uses the machine tool, it can reduce the probability of harm.

Firstly, please refer toFIGS. 1A and 1B, which respectively show an explosion diagram and a structural diagram of a protective apparatus applied to a machine tool according to a first exemplary embodiment of the present disclosure.

As shown inFIGS. 1A and 1B, the machine tool10includes an operational element110, a driving element120, and a protective apparatus130. The operational element110and the driving element120are configured on a machine table (as the machine table140shown inFIG. 1C). The operational element110can be a saw blade, a grinding wheel blade, or other type operational element. The driving element120can be a motor or other driving element which can work the operational element110. The present disclosure is not limited thereto. In the present disclosure, the operational element110is a saw blade, and the driving element120is a motor. Therefore, as shown inFIG. 1C, the user can use the machine tool10to work the saw blade through driving the motor, and accordingly cut an object to be sawed700(e.g., wood) on the machine table140, so that the object to be sawed700is cut to a suitable shape.

The protective apparatus130includes an insulating unit132, a conducting unit134, a capacitance sensor136, and a control unit138. The insulating unit132is configured between the operational element110and the driving element120, then the driving element120drives the operational element110through the insulating unit132. This means that the driving element120operates to work the insulating unit132and the operational element110. For example, the driving element120is a motor and the operational element110is a saw blade. The saw blade and the insulating unit132are configured on a drive shaft of the motor. The insulating unit132is configured between the drive shaft and the saw blade, so that the drive shaft is insulated from the saw blade. At this point, the operation of the drive shaft can work the insulating unit132and the saw blade.

The conducting unit134contacts the operational element110. In the present disclosure, the conducting unit134is a bearing and sleeves around the insulating unit132. The conducting unit134has a holding portion134aand a linking portion134bconfigured to the holding portion134a. The linking portion134bcontacts the operational element110. The holding portion134aelectrically connects to the capacitance sensor136. The linking portion134bof the conducting unit134is fixed to the insulating unit132, so that the insulating unit132is configured between the conducting unit134and the driving element120, to cause the conducting unit134to be insulated from the driving element120. Therefore, when the driving element120operates to work the insulating unit132, the linking portion134b, and the operational element110, the holding portion134aof the conducting unit134is immobile. In other disclosures, the conducting unit134is, for example, a ball bearing and sleeves around the insulating unit132. When the driving element120operates to rotate the linking portion134bof the ball bearing, the holding portion134aof the ball bearing is immobile.

In the present disclosure, the insulating unit132has a concave portion133and the concave portion133has a positioning end133a. In addition, the conducting unit134has a through-hole134ccorresponding to the shape of the concave portion133, and the operational element110has a through-hole112corresponding to the shape of the concave portion133. Therefore, the concave portion133of the insulating unit132can be configured through the through-hole134cof the conducting unit134and the through-hole112of the operational element110, so that the conducting unit134and the operational element110align the positioning end133aof the concave portion133. Therefore, the linking portion134bof the conducting unit134and the operational element110can be fixed to the concave portion133of the insulating unit132. The linking portion134bof the conducting unit134electrically connected to the operational element110does not fall off from the insulating unit132easily.

The capacitance sensor136electrically connects to the conducting unit134to sense the capacitance of the conducting unit134. The control unit138electrically connects between the capacitance sensor136and the driving element120. At present, because the capacitance sensor136electrically connects to the operational element110through the conducting unit134, the capacitance sensor136can detect the capacitance of the conducting unit134to determine whether an electric conductor approaches the operational element. This means that when the electric conductor (e.g., the user's hand) gradually approaches the operational element110, the capacitance of the conducting unit134increases gradually. Next, the capacitance sensor136determines whether the capacitance is more than a predefined value. When the capacitance sensor136determines that the capacitance is more than the predefined value, the distance between the electric conductor (e.g., the user's hand) and the operational element110is too close. At this time, the capacitance sensor136generates a stop signal to the control unit138. Then the control unit138controls the driving element120to stop driving the operational element120according to the stop signal, so that the insulating unit132, the linking portion134b, and the operational element110stop work.

Accordingly, the capacitance of the conducting unit134easily suffers from the interference of external conductors, e.g., the driving element120of the present disclosure, the motor, or etc. Therefore, the insulating unit132is configured between the operational element110and the driving element120, and the conducting unit134is configured to the insulating unit132. Therefore, the insulating unit132separates the driving element120, so that the conducting unit134is insulated from the driving element120and the operational element110is insulated from the driving element120, to avoid the electric power property of the driving element120in operation affecting the inducing capacitance between the operational element110and the conducting unit134. Therefore, the capacitance sensor136can detect the more accurate capacitance.

Next, the control unit138turns off the switch of the driving element120according to the stop signal, to stop the operation of the driving element120. Then when the capacitance sensor136determines that the capacitance of the conducting unit134is less than or equally to the predefined value, the control unit138restarts the driving element120, to re-operate the switch of the driving element120. In the present disclosure, the control unit138may be wired or wirelessly connect to the driving element120in a direct or indirect manner, and the present embodiment is not limited thereto.

In addition, in the present disclosure, the circuit structure of the capacitance sensor136can be implemented by an integrator. As shown inFIG. 1D, the capacitance sensor136includes a comparator COM and a feedback capacitance Ci. The positive input end (+) of the comparator COM receives a reference voltage Vref indicating the predefined value. The feedback capacitance Ci is connected between the negative input end (−) and the output end of the comparator COM. Furthermore, the negative input end (−) of the comparator COM receives the equivalent capacitance Cr and the mutual capacitance Cm. An end of the equivalent capacitance Cr electrically connects to the negative input end (−) of the comparator COM, and another end of the equivalent capacitance Cr connects to ground. An end of the mutual capacitance Cm electrically connects to the negative input end (−) of the comparator COM, and another end of the mutual capacitance Cm electrically connects to the operational element110. The equivalent capacitance Cr and the mutual capacitance Cm are connected in parallel with each other.

Therefore, when the electric conductor (e.g., the user's hand) does not approach the operational element110, the mutual capacitance Cm may sustain the fixed capacitance, and the negative input end (−) of the comparator COM receives the fixed value. When the electric conductor gradually approaches the operational element110, the capacitance gradually increases. In addition, when the electric conductor gradually approaches the operational element110to a predefined distance, the received value of the negative input end (−) of the comparator COM is more than the reference voltage Vref, to generate an output signal Vo with low voltage level. This means that the capacitance sensor136determines that the capacitance is more than the predefined value, to generate the stop signal to the control unit138. Next, the control unit138stops operating the driving element120according to the stop signal and then the linking portion134b, the insulating unit132, and the operational element110stop work, to avoid that the electric conductor (e.g., the user's hand) contacts the operational element110(e.g., the saw blade). The above circuit structure of the capacitance sensor136is described as an example, but another circuit structure of the capacitance sensor136may detect whether the distance between the electric conductor and the operational element110is too close. The present disclosure is not limited thereto.

In addition, because the operational element110has different sizes and types (e.g., the saw blade, the grinding wheel blade), the capacitance sensor136may sense different capacitance, causing the capacitance sensor136to determine inaccurate capacitance. For example, when the distance between the user's hand and the operational element110are too far, the capacitance sensor136still generates the stop signal to stop the operation of the driving element120. Therefore, the capacitance sensor136further includes a capacitance adjusting unit (not shown inFIG. 1A). The capacitance adjusting unit is used for adjusting the predefined value, so that the capacitance sensor136can adjust the predefined value according to different sizes or types of the operational element110, to determine the more accurate stop signal. More specifically, because the usage environment, the operational element110, and the user are different, the capacitance sensor136can determine the sensing distance by adjusting the predefined value.

Therefore, as shown inFIG. 1C, when the user uses the operational element110to cut the object to be sawed700(e.g., wood) on the machine table140of the machine tool10, the capacitance sensor136continuously determines whether the capacitance of the conducting unit134is more than the predefined value, to accordingly detect whether the user approaches the operational element110. When the capacitance sensor136determines that the capacitance of the conducting unit134is more than the predefined value (i.e., the distance between the user and the operational element110is too close), the capacitance sensor136generates the stop signal to the control unit138. The control unit138stops operating the driving element120according to the stop signal, and then the linking portion134b, the insulating unit132, and the operational element110stop work, to avoid the user being in direct contact with the operational element110and getting harmed.

Next, please refer toFIG. 2, which shows an explosion diagram of a machine tool according to another exemplary embodiment of the present disclosure. As shown inFIG. 2, the machine tool20includes an operational element210, a driving element220, and a protective apparatus230. The operational element210and the driving element220are configured on a machine table (not shown inFIG. 2). The operational element210can be a saw blade, a grinding wheel blade, or other type operational element. The driving element220can be a motor or other driving element which can work the operational element210. The present disclosure is not limited thereto. In the present disclosure, the driving element220is a motor.

The protective apparatus230includes an insulating unit232, a conducting unit234, a capacitance sensor236, and a control unit238. The insulating unit232is configured between the operational element210and the driving element220. Then the driving element220drives the operational element210through the insulating unit232. This means that the driving element220operates to work the insulating unit232and the operational element210.

The conducting unit234contacts the operational element210. In the present disclosure, the conducting unit234is a bearing and sleeves around the insulating unit232. The conducting unit234has a holding portion234aand a linking portion234bconfigured to the holding portion234a. The linking portion234bcontacts the operational element210. The holding portion234aelectrically connects to the capacitance sensor236. In addition, the linking portion234bof the conducting unit234is fixed to the insulating unit232, so that the insulating unit232is configured between the conducting unit234and the driving element220, to cause the conducting unit234to be insulated from the driving element220. Therefore, when the driving element220operates to work the insulating unit232, the linking portion234b, and the operational element210, the holding portion234aof the conducting unit234is immobile. In other disclosures, the conducting unit234is, for example, a ball bearing and sleeves around the insulating unit232. When the driving element220operates to rotate the linking portion234bof the ball bearing, the holding portion234aof the ball bearing is immobile.

In the present disclosure, the insulating unit232has a concave portion233and the concave portion233has a positioning end233a. In addition, the conducting unit234has a through-hole234ccorresponding to the shape of the concave portion233. Therefore, the concave portion233of the insulating unit232can be configured through the through-hole234cof the conducting unit234, so that the through-hole234cof the conducting unit234aligns the positioning end233aof the concave portion233. Therefore, the linking portion234bof the conducting unit234can be fixed to the concave portion233of the insulating unit232, and does not fall off from the insulating unit232easily. The end portion212of the operational element210can be inserted and fixed into the hole (not shown inFIG. 2) of the insulating unit232, and further descriptions are hereby omitted. It is worth to note that although the end portion212of the operational element210is fixed into the hole of the insulating unit232, the operational element210is insulated from the driving element220, the conducting unit234is insulated from the driving element220, and the operational element210electrically contacts the linking portion234bof the conducting unit234. Therefore, the above connection relationships and operations can avoid the electric power property of the driving element220in operation affecting the inducing capacitance between the operational element210and the conducting unit234.

The capacitance sensor236electrically connects to the conducting unit234to sense the capacitance of the conducting unit234. The control unit238electrically connects between the capacitance sensor236and the driving element220. With respect to operation of the capacitance sensor236and the control unit238, it is the same as that of the capacitance sensor136and the control unit138, so a detailed description is omitted. The difference is that the control unit238directly turns off the power222of the driving element220according to the stop signal, to stop the operation of the driving element220. Therefore, when the capacitance sensor236determines that the capacitance of the conducting unit234is more that the predefined value, this means that the distance between the electric conductor (e.g., the user's hand) and the operational element210is too close. Then the capacitance sensor236generates the stop signal to the control unit238. The control unit238directly turns off the power222of the driving element220according to the stop signal to stop operating the driving element220, so that the insulating unit232, the linking portion234b, and the operational element110stop work.

Accordingly, the present embodiment inFIG. 2needs to additionally design the turn on/off operation of the power of the driving element220. The foregoing embodiment inFIG. 1Aneeds to additionally design the turn on/off operation of the switch of the driving element120. Because the internal structure of the driving element120shown inFIG. 1Ais more complex than that of the power222in the present embodiment, the turn on/off operation configured in the power222is easier than the turn on/off operation configured in the driving element120shown inFIG. 1A.

Reference is made toFIGS. 3A and 3B, whereinFIG. 3Ais an explosion diagram of a protective apparatus applied to a machine tool according to a second exemplary embodiment of the present disclosure; FIG.3B is a structural diagram of the protective apparatus applied to the machine tool according to the second exemplary embodiment of the present disclosure.

As shown inFIG. 3A, the protective apparatus130includes the insulating unit132, the conducting unit134, the capacitance sensor136and the control unit138. The machine tool includes the operational element110such as the saw blade in the embodiment, and the driving element120.

Differences between the first and second exemplary embodiments are described in the following. As shown inFIG. 3A, in the second exemplary embodiment, the operational element110of the machine tool is provided between the conducting unit134of the protective apparatus and the driving element120of the machine tool. Therefore, the conducting unit134of the second exemplary embodiment can be more easily disassembled and replaced with a new one.

As shown inFIGS. 3A and 3B, the concave portion133of the insulating unit132is configured through the through-hole112of the operational element110and the through-hole134cof the conducting unit134. The conducting unit134is in direct contact with a surface of the operational element110opposite to the driving element120.

The capacitance sensor136is electrically connected to the conducting unit134and configured to sense the capacitance of the conducting unit134. The control unit138is electrically connected to the capacitance sensor136and the driving element120, and configured to control the driving element120to rotate according to the sense capacitance.

In addition, the conducting unit134may include liquid mercury as a conductive medium. Therefore, noise generated by the conducting unit134is lower than that of the conventional element including a carbon brush.

Reference is further made toFIG. 3C, which is a diagram of the protective apparatus operating in a correction mode and being configured to a machine table having a front correction region and a side correction region on which the user places his or her hand according to the second exemplary embodiment of the present disclosure.

As shown inFIG. 3C, a front correction region R1is defined. The front correction region R1is located near the saw teeth of the operational element110of the machine tool. In the embodiment, the front correction region R1is located in front of the operational element110. An object such as wood is to be cut by the saw teeth of the operational element110.

In practice, if the object is to be cut by the machine tool is at a back side of the operational element110, the front correction region R1or other regions may be defined at the back side of the operational element110.

Before the operational element110such as the saw blade is driven by the driving element120, the protective apparatus operates in the correction mode.

The control unit138may include a control element and a promoting element. In the correction mode, the control element may control the promoting element to output a first prompting signal for prompting the user to place his or her hand in the front correction region R1located in front of the saw teeth of the operational element110without contacting with the operational element110. The first prompting signal outputted by the control unit138may be a visual signal and/or audio signal, but the present disclosure is not limited thereto.

As shown inFIG. 3A, the front correction region R1is marked on the machine table140. However, in practice, the front correction region R1or other correction regions may not be marked. The first prompting signal outputted by the control unit138may prompt the user to place his or her hand on any position spaced from the saw teeth of the operational element110at a first distance.

The position at which the user places his or her hand is defined as the front correction region R1. If the first distance between the operational element110of the machine tool and the front correction region R1in which the user places his or her hand is not equal to 0 cm, it means that the hand of the user in the front correction region R1is not in contact with the operational element110.

In detail, the first prompting signal outputted by the control unit138may prompt the user to place his or her hand on a position, which is spaced from the saw teeth of the operational element110at the first distance and spaced from the machine table140at a second distance. The second distance may depend on a height of the object to be cut by the operational element110of the machine tool. For example, the object may be the wood shown inFIG. 3D. If the second distance between the machine table140and the hand of the user is not equal to 0 cm, it means that the hand of the user in the front correction region R1is not in contact with the machine table140.

An area of the front correction region R1may depend on a length and a width of a forefinger of a left hand or a right hand of the user. As shown inFIG. 3, the user places only a forefinger in the front correction region R1. In practice, the front correction region R1may match a shape of the entire hand, and the user may place all his or her fingers in the front correction region R1.

The distance between the operational element110and the front correction region R1may be larger than a first distance threshold and smaller than a second distance threshold. For example, the first distance threshold may be 0 cm and the second distance threshold may be a value larger than 0 cm, but the present disclosure is not limited thereto. The second distance threshold depends on a range in which the capacitance of the conducting unit134varies with the user's hands.

It is worth noting that, when the protective apparatus operates in the correction mode, the capacitance sensor136obtains a reference capacitance from the control unit138or an external circuit. Further, when the hand of the user is in the front correction region R1without contacting with the operational element110, the capacitance sensor136senses a first capacitance of the conducting unit134.

The control unit138receives the first capacitance of the conducting unit134from the capacitance sensor136. The control unit138then calculates a capacitance threshold according to the reference capacitance and the first capacitance. The control unit138may store the capacitance threshold. The capacitance threshold may be larger than the reference capacitance and smaller than the first capacitance.

In addition, as shown inFIG. 3C, a side correction region R2is defined. In practice, the side correction region R2may be omitted. The side correction region R2is spaced from a surface of the body of the operational element110opposite to the driving element120at a third distance. The third distance between the surface of the body of the operational element110and the side correction region R2may be or not be equal to the first distance between the operational element110and the front correction region R1.

The control unit138outputs a second prompting signal for prompting the user to place his or her hand in the side correction region R2in the correction mode. When the hand is in the side correction region R2without contacting with the operational element110, the capacitance sensor136senses a second capacitance of the conducting unit134. The control unit138calculates the capacitance threshold according to the reference capacitance, the first capacitance and second capacitance. The capacitance threshold is smaller than the second capacitance and the first capacitance and larger than the reference capacitance.

It should be understood that the front correction region R1and the side correction region R2may be defined in different positions in practice. The user may place his or her hand in different positions. The sensed first and second capacitances of the conducting unit134vary with a position of the hand of the user relative to the operational element110.

Alternatively, more correction regions may be defined and located in positions different from the positions of the front correction region R1and the side correction region R2. The user may place his or her hand sequentially on these correction regions. Under this condition, the capacitance sensor136may sequentially sense capacitances of the conducting unit134that may include the first capacitance and the second capacitance.

Reference is further made toFIG. 3D, which is a diagram of the protective apparatus operating in a protection mode for protecting the user's hand from being injured by the machine tool cutting a wood.

As shown inFIGS. 3Band D, when the operational element110is driven by the driving element120, the conducting unit134maintains contact with the surface of the operational element110opposite to the driving element120, the protective apparatus enters the protection mode.

In the protection mode, the capacitance sensor236senses a practical capacitance of the conducting unit134that is generated when the user's hand holding and moving the object such as the wood to be cut toward the operational element110being driven by the driving element120.

The practical capacitance of the conducting unit134may vary with the distance between the hand of the user and the operational element110. The practical capacitance may include a capacitance of the operational element110and a capacitance of the hand of the user. When the user moves his or her hand to other positions, the capacitance sensor236may sense different practical capacitances of the conducting unit134.

The control unit138compares the calculated capacitance threshold and the practical capacitance sensed when the object such as the wood is cut by the machine tool. It should be understood that the smaller the distance between the operational element110and the hand of the user is, the larger the sensed practical capacitance is.

When the control unit138determines that the practical capacitance is larger than the capacitance threshold, the control unit138determines that the user is too close to the operational element110. Under this condition, the control unit138controls the driving element120of the machine tool to stop driving the operational element110of the machine tool before the user contacts with the operational element110. Therefore, the protective apparatus can prevent the user from being injured by contact with the operational element110being driven by the driving element120.

Reference is made toFIG. 4A, which is a flowchart diagram of a protective method for controlling operation of a machine tool by using a protective apparatus in a correction mode according to a third exemplary embodiment of the present disclosure.

As shown inFIG. 4A, the protective method for controlling operation of the machine tool by using the above protective apparatus includes the following steps S401to S409.

In step S401, the protective apparatus that operates in the correction mode before the saw blade is driven by the driving element is provided.

In step S403, the control unit outputs the first prompting signal for prompting the user to place his or her hand in the front correction region located in front of the saw teeth of the saw blade.

In step S405, the capacitance sensor obtains the reference capacitance.

In step S407, the capacitance sensor senses the first capacitance of the conducting unit that is generated when the hand of the user is in the front correction region without contacting with the saw blade.

In step S409, the control unit calculates the capacitance threshold according to the reference capacitance and the first capacitance, wherein the capacitance threshold is larger than the reference capacitance and smaller than the first capacitance.

Reference is made toFIG. 4B, which is a flowchart diagram of the protective method for controlling operation of the machine tool by using a protective apparatus in a protection mode according to the third exemplary embodiment of the present disclosure.

As shown inFIG. 4B, the protective method for controlling operation of the machine tool by using the above protective apparatus includes the following steps S411to S417.

In step S411, the protective apparatus controls the driving element to drive the driving element.

In step S413, when the saw blade is driven by the driving element, the protective apparatus enters the protection mode and the conducting unit maintains contact with the saw blade.

In step S415, the capacitance sensor senses the practical capacitance of the conducting unit that is generated when the user moves his or her hand toward the saw teeth of the saw blade for cutting the object.

In step S417, it is determined whether or not the practical capacitance is larger than the capacitance threshold. If the practical capacitance is determined to be not larger than the capacitance threshold, step S411is performed again. If the practical capacitance is determined to be larger than the capacitance threshold, step S419is performed.

In step S419, the control unit of the protective apparatus controls the driving element of the machine tool to stop driving the saw blade.

Reference is made toFIG. 5A, which is a waveform diagram of a sensing signal of a first capacitance of the conducting unit sensed when a distance of about 1 cm is between the hand of the user and the operational element according to the exemplary embodiments of the present disclosure.

As shown inFIG. 5A, a vertical axis represents a reference value that is converted from the mutual capacitance Cm, and a horizontal axis represents a time during which the operational element110is driven to operate.

When the operational element110is driven by the driving element120and the distance of about 1 cm is between the operational element and the first correction region R1in which the user places his or her hand, the capacitance sensor136senses the first capacitance of the conducting unit in the to generate the sensing signal indicating the first capacitance of 300 pF.

Reference is made toFIG. 5B, which is a waveform diagram of the filtered sensing signal of the first capacitance of the conducting unit sensed when the distance of about 1 cm is between the hand of the user and the operational element according to the exemplary embodiments of the present disclosure.

The sensing signal sensed by the capacitance sensor136may be filtered by a filter included in the protective apparatus to generate the filtered sensing signal as shown inFIG. 5B. The control unit can obtain the correct time constant and the capacitance according to the filtered sensing signal.

Reference is made toFIG. 6A, which is a waveform diagram of a sensing signal of the first capacitance of the conducting unit sensed when a distance of about 0.5 cm is between the hand of the user and the operational element according to the exemplary embodiments of the present disclosure.

When the operational element110is driven by the driving element120and the distance of about 0.5 cm is between the operational element and the first correction region R1in which the user places his or her hand, the capacitance sensor136senses the first capacitance of the conducting unit to generate the sensing signal indicating the first capacitance of 460 pF.

Reference is made toFIG. 6B, which is a waveform diagram of the filtered sensing signal of the second capacitance of the conducting unit sensed when a distance of about 0.5 cm is between the hand of the user and the operational element according to the exemplary embodiments of the present disclosure.

The sensing signal sensed by the capacitance sensor136may be filtered by the filter included in the protective apparatus to generate the filtered sensing signal as shown inFIG. 6B. The control unit can obtain the correct time constant and the capacitance according to the filtered sensing signal.

As described above, it is apparent that the smaller the distance between the operational element110and the hand of the user is, the larger the sensed practical capacitance is.

Reference is made toFIG. 7A, which is a waveform diagram of a second sensing signal of a second capacitance of the conducting unit sensed when a distance of about 1 cm is between the hand of the user and the operational element according to the exemplary embodiments of the present disclosure.

When the operational element110is driven by the driving element120and the distance of about 1 cm is between the operational element and the second correction region R2in which the user places his or her hand, the capacitance sensor136senses the second capacitance of the conducting unit to generate the sensing signal indicating the first capacitance of 400 pF.

Reference is made toFIG. 7B, which is a waveform diagram of the filtered second sensing signal of the second capacitance of the conducting unit sensed when the distance of about 1 cm between the hand of the user and the operational element according to the exemplary embodiments of the present disclosure.

The sensing signal sensed by the capacitance sensor136may be filtered by the filter included in the protective apparatus to generate the filtered sensing signal as shown inFIG. 7B. The control unit can obtain the correct time constant and the capacitance according to the filtered sensing signal.

Reference is made toFIG. 8A, which is a waveform diagram of a second sensing signal of the second capacitance of the conducting unit sensed when a distance of about 0.5 cm is between the hand of the user and the operational element according to the exemplary embodiments of the present disclosure.

When the operational element110is driven by the driving element120and the distance of about 0.5 cm is between the operational element and the second correction region R2in which the user places his or her hand, the capacitance sensor136senses the second capacitance of the conducting unit to generate the sensing signal indicating the second capacitance of 600 pF.

As described above, it is apparent that the smaller the distance between the operational element110and the hand of the user is, the larger the sensed practical capacitance is.

Reference is made toFIG. 8B, which is a waveform diagram of the filtered second sensing signal of the second capacitance of the conducting unit sensed when the distance of about 0.5 cm is between the hand of the user and the operational element according to the exemplary embodiments of the present disclosure.

The sensing signal sensed by the capacitance sensor136may be filtered by the filter included in the protective apparatus to generate the filtered sensing signal as shown inFIG. 8B. The control unit can obtain the correct time constant and the capacitance according to the filtered sensing signal.

Reference is made toFIG. 9, which is a waveform diagram of a capacitance of the conducting unit sensed when the hand of the user is in contact with the operational element according to the exemplary embodiments of the present disclosure.

When the operational element110is driven by the driving element120and the hand of the user is in contact with the operational element110, the capacitance sensor136senses the capacitance of the conducting unit to generate the sensing signal indicating the capacitance of 95.8 mF, wherein the sensed capacitance may be as the reference capacitance.

In summary, for the protective apparatus and the machine tool of the present disclosure, a capacitance sensor and an operational element are electrically connected with each other, so that the capacitance sensor does not have the blind spot problem for the capacitance sensor configuring the different position of the operational element. Therefore, when the user uses a machine tool, the protective apparatus and the machine tool can reduce the probability of harm.

The above-mentioned descriptions represent merely the exemplary embodiment of the present disclosure, without any intention to limit the scope of the present disclosure thereto. Various equivalent changes, alterations or modifications based on the claims of present disclosure are all consequently viewed as being embraced by the scope of the present disclosure.