US20140182430A1 - Saw Device with Detection System - Google Patents

Abstract

A power tool includes a swing arm movable along a swing arm path, an actuating assembly configured to transfer a force to the swing arm, a control system configured to control the actuating assembly to transfer a force to the swing arm, and a detection system configured to detect the operability of the actuating assembly.

Description

FIELD
• The present disclosure relates to power tools and more particularly to power tools with exposed shaping devices.
BACKGROUND
• A number of power tools have been produced to facilitate forming a work piece into a desired shape. One such power tool is a saw device. A wide range of saw device are available for a variety of uses. For example, some saw device such a cabinet table saws are very heavy and relatively immobile. Other table saws, sometimes referred to as jobsite table saws, are relatively light. Jobsite table saws are thus portable so that a worker can position the table saw at a job site. Some accuracy is typically sacrificed in making a table saw sufficiently light to be mobile. The convenience of locating a table saw at a job site, however, makes job site table saws very desirable in applications such as general construction projects.
• All table saws, including cabinet table saws and job site table saws, present a safety concern because the saw blade of the table saw is typically very sharp and moving at a high rate of speed. Accordingly, severe injury such as severed digits and deep lacerations can occur almost instantaneously. A number of different safety systems have been developed for table saws in response to the dangers inherent in an exposed blade moving at high speed. One such safety system is a blade guard. Blade guards movably enclose the saw blade, thereby providing a physical barrier that must be moved before the rotating blade is exposed. While blade guards are effective to prevent some injuries, the blade guards can be removed by a user either for convenience of using the table saw or because the blade guard is not compatible for use with a particular shaping device. By way of example, a blade guard is typically not compatible with a dado blade and must typically be removed when performing non-through cuts.
• Table saw safety systems have also been developed which are intended to stop the blade when a user's hand approaches or touches the blade. Various stopping devices have been developed including braking devices which are physically inserted into the teeth of the blade. More recently, systems have been developed which physically move the blade or other shaping instrument below the support surface of the device. One such device incorporates a swing arm assembly which supports a blade above a work piece support surface and swings the blade beneath the work piece support surface when an unsafe condition is sensed. Regardless of the mechanism which is used to physically render a power tool safe, an associated control system must be functional. This is particularly important in systems which incorporate single use devices such as a pyrotechnic charge to move a blade away from a user.
• In view of the foregoing, it would be advantageous to provide a power tool with a mitigation system that evaluates the operational status of the mitigation system. A mitigation system that evaluates the same circuitry used to activate a mitigation mechanism would also be advantageous.
SUMMARY
• In accordance with one embodiment a table saw includes a latch hold mechanism, a swing arm movable along a swing arm path between a first position adjacent the latch hold mechanism and a second position spaced apart from the latch hold mechanism, a latch movable between a first position whereat the swing arm is maintained at the first position and a second position whereat the swing arm is not maintained at the first position, an actuating assembly configured to transfer a force to the swing arm when the swing arm is maintained at the first position, a control system configured to control the actuating assembly to transfer a force to the swing arm when the swing arm is maintained at the first position sufficient to move the latch from the first position to the second position, and a detection system configured to detect the operability of the actuating assembly.
• In another embodiment, a power tool includes a work-piece support surface, a swing arm assembly movable along a swing path between a first swing arm position whereat a portion of a shaping device supported by the swing arm assembly extends above the work-piece support surface and a second swing arm position whereat the portion of the shaping device does not extend above the work-piece support surface, an actuating assembly configured to force the swing arm assembly away from the first swing arm position and toward the second swing arm position, a control system configured to activate the actuating assembly in response to a sensed condition, and a detection system configured to test the functionality of the actuating assembly without activating the actuating assembly.
BRIEF DESCRIPTION OF THE DRAWINGS
• The accompanying drawings illustrate various embodiments of the present disclosure and together with a description serve to explain the principles of the disclosure.
• FIG. 1 depicts a top perspective view of a table saw incorporating a mitigation system in accordance with principles of the invention;
• FIG. 2 depicts a side plan view of a carriage assembly, solenoid, and latch assembly of the table saw ofFIG. 1 with the swing arm assembly latched;
• FIG. 3 depicts a side plan view of the solenoid and latch assembly of the table saw ofFIG. 1;
• FIG. 4 depicts schematic of the mitigation and control system of the table saw ofFIG. 1;
• FIG. 5 depicts a schematic of the detection system ofFIG. 4;
• FIG. 6 depicts a table of the outputs of the comparator block of the detection system ofFIG. 5; and
• FIG. 7 depicts a side plan view of the table saw ofFIG. 1 with the swing arm assembly unlatched.
• Corresponding reference characters indicate corresponding parts throughout the several views. Like reference characters indicate like parts throughout the several views.
DETAIL DESCRIPTION OF THE DISCLOSURE
• While the power tools described herein are susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit the power tools to the particular forms disclosed. On the contrary, the disclosure is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure as defined by the appended claims.
• Referring toFIG. 1, asaw device100 is shown with a base housing (not shown) removed. The saw device may be, such as, a table saw, a miter saw, a bevel saw, a compound saw, a vertical saw, a stationary saw, a machine saw, a band saw, a jig saw, a chain saw, a circular saw, or other cutting devices with a saw blade. The illustrated device as shown inFIG. 1 is a table saw. Thetable saw100 includes a workpiece support surface104. A riving knife orsplitter106 is positioned adjacent to ablade108 which extends from within the base housing (not shown) to above the work-piece support surface104. A blade guard (not shown) may be attached to thesplitter106. The angle of theblade108 with respect to the work-piece support surface104 is established by pivoting aframe114 within the base housing (not shown).
• Theframe114 supports astop pad116. Theframe114 further supports acarriage assembly120 shown inFIG. 2. Thecarriage assembly120 includes acarriage122 which supports amotor124 which is powered through a power switch (not shown) located on the base housing (not shown). Thecarriage122 is slidably mounted on twoguiderails126/128. The position of thecarriage122 along theguiderails126/128 is controlled by a blade height turn-wheel130 through a gearing assembly (not shown) which is connected to ascrew post132. Thecarriage124 pivotably supports alatch assembly140 and pivotably supports aswing arm assembly142.
• Theswing arm assembly142, also shown inFIG. 3, includes ahousing144. Astrike bolt146 is mounted on thehousing144. Thehousing144 encloses apower wheel150 that is driven by anoutput shaft152 of themotor124. Abelt154 transfers rotational movement from thepower wheel150 to ablade wheel156. Anut158 is used to affix the blade108 (not shown inFIGS. 2 and 3 for purpose of clarity) to ashaft160 of theblade wheel156. Atensioner162 maintains thebelt154 at a desired tension.
• Asolenoid assembly164 is an actuating assembly which includes asolenoid pin166 which is aligned with thestrike bolt146 when theswing arm assembly142 is in a latched position as depicted inFIG. 3. Thesolenoid assembly164, in the embodiment ofFIGS. 1-3, is a pyrotechnically activated system wherein a pyrotechnic charge is positioned within a receptacle which in this embodiment is acylinder portion170 which is closed at one end by acap172. Operation of thesolenoid assembly164 is controlled by acontrol module174 which is part of a mitigation andcontrol system180 depicted inFIG. 4.
• The mitigation andcontrol system180 includes asensing system182, acontroller184, themotor124, adetection system186, and apyrotechnic module188. Thesensing system182 in different embodiments is any desired sensing circuit. One acceptable sensing system is a part of the sensing and control circuit described in U.S. Pat. No. 6,922,153, the entire contents of which are herein incorporated by reference. The safety detection and protection system described in the '153 patent senses an unsafe condition and provides a sense signal indicative of the sensed unsafe condition.
• Thecontroller184 one embodiment comprises a microprocessor, ASIC or other type of processing unit. Thecontroller184 receives the sense signal from thesensor subsystem182 and, in response to an unsafe condition, fires thepyrotechnic module188 as discussed more fully below.
• Thedetection system186 is shown in further detail inFIG. 5. Thedetection system186 includes aswitch190, adifferential block192, acomparator block194, and aresistor196. Thecontroller184,switch190,differential block192,comparator block194, andresistor196 are located within the mitigationsystem control module174 while thepyrotechnic module188 is located within thecylinder portion170 of thesolenoid assembly164. Further details of the mitigation andcontrol system180 are provided in the following description of the operation of the table saw100.
• Operation of the table saw100 is described with initial reference toFIGS. 1-3. Initially, theswing arm assembly142 is maintained in a latched position with theswing arm housing144 supported by thelatch assembly140 as shown inFIG. 3. In this position, theblade wheel156 is positioned sufficiently close to the work-piece support surface104 that theblade108 extends above the work-piece support surface104 as shown inFIG. 1. A user operates a bevel adjust turn wheel (not shown) to pivot theframe114 with respect to the work-piece support surface104 to establish a desired angle between theblade108 and the work-piece support surface104. The user further operates the blade height adjustment turn-wheel130 to move thecarriage122 along theguiderails126/128 to establish a desired height of theblade108 above the work-piece support surface104.
• Using the power switch (not shown), power is applied to themotor124 under the control of thecontroller184. Specifically, positioning of the switch causes the mitigation andcontrol system180 to be energized. Upon energization of the mitigation andcontrol system180, thecontroller184 controls theswitch element190 to a closed position thereby applying a voltage from a stable DC power rail to thecylinder portion170. The current (also referred to herein as a “test signal”) allowed through theswitch element190, typically on the order of milliamps, is selected to be much less than the current required to fire or activate (hereinafter also referred to as a “firing current”) thepyrotechnic module188. Accordingly, if apyrotechnic module188 is loaded in thecylinder portion170, thepyrotechnic module188 does not fire and a voltage differential is developed across thepyrotechnic module188.
• The developed voltage difference is applied to thedifferential amplifier block192 and an amplified voltage signal based upon the developed voltage difference is provided as an output of thedifferential amplifier block192. The output of thedifferential amplifier block192 is applied to afirst comparator200 which compares the output to a first reference voltage202. The first reference voltage is selected to be slightly lower than the expected lowest output of thedifferential amplifier block192 if a pyrotechnic module is positioned within thecylinder portion170. By way of example, in one embodiment a pyrotechnic module exhibits a range of resistance between 1.7-2.3 ohms, dependent upon temperature. Accordingly, the first reference voltage202 is set to the expected output of thedifferential amplifier block192 for a resistance of 1.6 ohms across thecylinder portion170. Consequently, thefirst comparator200 outputs a high value to thecontroller184.
• The output of thedifferential amplifier block192 is also applied to asecond comparator204 which compares the output to asecond reference voltage206. The second reference voltage is selected to be slightly higher than the expected highest output of thedifferential amplifier block192 if a pyrotechnic module is positioned within thecylinder portion170. Using the example above, thesecond reference voltage206 is set to the expected output of thedifferential amplifier block192 for a resistance of 2.4 ohms across thecylinder portion170. Consequently, thesecond comparator204 outputs a high value to thecontroller184.
• Thecontroller184 is configured such that when two high values are received from thecomparator block194, power can be applied to themotor124. Accordingly, so long as a properly functioningpyrotechnic module188 is loaded within thecylinder190, themotor124 can be energized when the power switch (not shown) is manipulated by a user.
• In the event that nopyrotechnic module188 is loaded within thecylinder170, then there is no voltage drop across theresistor196. Accordingly, the voltage drop applied to thedifferential amplifier block194 will be much higher than the voltage applied when apyrotechnic module188 is loaded. Using the above described example, since the first reference voltage202 is set to the expected output of thedifferential amplifier block192 for a resistance of 1.6 ohms across thecylinder portion170, thefirst comparator200 outputs a high value to thecontroller184. However, since thesecond reference voltage206 is set to the expected output of thedifferential amplifier block192 for a resistance of 2.4 ohms across thecylinder portion170 and the output of thedifferential amplifier block192 is subtracted from thesecond reference voltage206, thesecond comparator204 outputs a low value to thecontroller184.
• Therefore, if there is nopyrotechnic module188, or if the loadedpyrotechnic module188 has already been fired and is no longer operable, thecontroller184 will not allow power to be applied to themotor124.
• In the event that a defectivepyrotechnic module188 is loaded within thecylinder170 which results in a short circuit (or in any other event leading to a short circuit within the cylinder portion170), then there is no voltage drop across thecylinder portion170. Accordingly, the voltage drop applied to thedifferential amplifier block194 will be much lower than the voltage applied when apyrotechnic module188 is loaded. Using the above described example, since the first reference voltage202 is set to the expected output of thedifferential amplifier block192 for a resistance of 1.6 ohms across thecylinder portion170, thefirst comparator200 outputs a low value to thecontroller184. Since thesecond reference voltage206 is set to the expected output of thedifferential amplifier block192 for a resistance of 2.4 ohms across thecylinder portion170 and the output of thedifferential amplifier block192 is subtracted from thesecond reference voltage206, thesecond comparator204 outputs a high value to thecontroller184.
• Therefore, if there is a defectivepyrotechnic module188, or if there is another condition resulting in a short circuit within thecylinder portion170, thecontroller184 will not allow power to be applied to themotor124.
• The above described scenarios are depicted in tabular form inFIG. 6. The mitigation andcontrol system180 thus ensures that the mitigation system is functional prior to allowing power to be applied to themotor124. Additionally, in some embodiments thecontroller184 is configured to periodically apply the DC rail voltage through theswitch element190 during operation of themotor124. Accordingly, if thepyrotechnic module188 becomes dysfunctional during operation of the table saw100, the power to themotor124 is interrupted.
• Continuing with a description of the operation of the table saw100, once the mitigation andcontrol system180 verifies that thepyrotechnic module188 is installed and functional, power is applied to themotor124 causing theoutput shaft152 and thepower wheel150 to rotate. Rotation of thepower wheel150 causes thebelt154 to rotate theblade wheel156 and theblade108 which is mounted on theblade wheel156. A work-piece may then be shaped by moving the work-piece into contact with theblade108.
• During operation of the table saw100, the mitigation andcontrol system180 monitors for an unsafe condition using thesensor system182. If an unsafe condition is detected, thecontroller184 actuates thepyrotechnic module188. Upon actuation of thepyrotechnic module188, thesolenoid pin166 is forced outwardly from thesolenoid assembly164. When theswing arm assembly142 is maintained in a latched position with thehousing144 supported by thelatch assembly140 as shown inFIG. 3, thestrike bolt146 is aligned with thesolenoid pin166. Accordingly, as thesolenoid pin166 is forced out of thesolenoid assembly164, thesolenoid pin166 impacts thestrike bolt146.
• The shape of thehousing144 and thelatch assembly140 is selected such that the impact of thesolenoid pin166 on thestrike bolt166 generates a force tending to rotate thelatch assembly140 in the direction of thearrow210 inFIG. 3 against aspring212. The spring constant of thespring212 and the force generated by thepyrotechnic module188 are selected such that when thesolenoid pin166 impacts thestrike bolt146 the generated force is sufficient to compress thespring212 and to force thelatch assembly140 to rotate into a position whereat theswing arm assembly142 is no longer maintained in position adjacent to thelatch assembly140. Consequently, theswing arm assembly142 pivots about theoutput shaft152 in the direction of thearrow214 ofFIG. 3 such that theblade wheel156 moves away from the work-piece support surface104 to the position shown inFIG. 7. Accordingly, the blade108 (not shown inFIG. 7 for purpose of clarity) is pulled by theswing arm assembly142 in a direction away from the work-piece support surface104.
• Once thepyrotechnic module188 has fired, thepyrotechnic module188 no longer provides a path for current to flow. Accordingly, the firedpyrotechnic module188 is an electrical “open” for the purposes of thedetection circuit186. Consequently, until thepyrotechnic module188 is replaced, thesecond comparator204 outputs a low signal and power is not provided to themotor124.
• Once the sensed condition has been cleared, theswing arm assembly142 is reset by moving thelatch assembly140 out of the swing path. This is effected by compressing thespring212. Theswing arm assembly142 may then be rotated in a counterclockwise direction about theoutput shaft152 until thehousing144 is adjacent to thelatch assembly140. Thelatch assembly140 is then released and thespring212 biases thelatch assembly140 into contact with thehousing144, returning to the condition ofFIG. 3.
• The table saw100 thus actively monitors for an unsafe condition and initiates mitigation action automatically in the event an unsafe condition is sensed. Additionally, the table saw100 ensures that a functionalpyrotechnic device188 is loaded before allowing or continuing to allow energy to be supplied to themotor124.
• The mitigation system discussed with respect to the table saw100 can be implemented using very light materials, and is thus amenable to incorporation into a variety of power tools including bench top saws and portable saws. For example, the components which are subjected to increased stress within the mitigation system, such as thesolenoid pin166,swing arm assembly142, and thestrike bolt146, can be made of more durable materials including metals to withstand the impacts and stresses of activating the mitigation system. Other components, including the housings, may be fabricated from more lightweight materials to minimize the weight of the power tool.
• While the invention has been illustrated and described in detail in the drawings and foregoing description, the same should be considered as illustrative and not restrictive in character. It is understood that only the preferred embodiments have been presented and that all changes, modifications and further applications that come within the spirit of the invention are desired to be protected.

Claims (16)

1. A saw device, comprising:

a swing arm movable along a swing arm path between a first swing arm position and a second swing arm position;

an actuating assembly configured to transfer a force to the swing arm resulting in a bias on the swing arm in a direction toward the swing arm position;

a control system configured to control the actuating assembly; and

a detection system configured to detect the operability of the actuating assembly without activating the actuating assembly.

2. The saw device ofclaim 1, wherein the control system is configured such that power is not provided to a motor of the saw device when the detection system outputs a signal indicating that the actuating assembly is not operable.

3. The saw device ofclaim 2, wherein:

the actuating assembly includes a pyrotechnic module;

the detection system includes a comparator block;

the comparator block is configured to generate a first output when the pyrotechnic module is installed in the actuating assembly;

the comparator block is configured to generate a second output when the pyrotechnic module acts as an open or is not installed in the actuating assembly;

the comparator block is configured to generate a third output when the pyrotechnic module acts as a short in the actuating assembly; and

each of the first output, the second output, and the third output is different from the other of the first output, the second output, and the third output.

4. The saw device ofclaim 3, wherein the comparator block comprises:

a first comparator;

a first voltage reference operably connected to the first comparator;

a second comparator; and

a second voltage reference operably connected to the second comparator.

5. The saw device ofclaim 4, wherein:

the first voltage reference is configured to apply a first reference signal to a first input of the first comparator which is less than the expected lowest signal applied to a second input of the first comparator when the pyrotechnic module is positioned within the actuating assembly and a test signal is applied to the pyrotechnic module; and

the second voltage reference is configured to apply a second reference signal to a first input of the second comparator which is greater than the expected highest signal applied to a second input of the second comparator when the pyrotechnic module is positioned within the actuating assembly and the test signal is applied to the pyrotechnic module.

6. The saw device ofclaim 5, further comprising:

a receptacle configured to receive the pyrotechnic module; and

a differential amplifier block configured to detect a voltage difference across the receptacle when the test signal is applied to the receptacle, the differential amplifier block including an output operably connected to the second input of the first comparator and the second input of the second comparator.

7. The saw device ofclaim 6, further comprising:

a switch element having an input operably connected to a power supply and an output operably connected to the receptacle; and

a controller operably connected to an output of the first comparator and an output of the second comparator, the controller operably connected to the switch element for selectively operably connecting the power supply to the receptacle through the switch element.

8. The saw device ofclaim 7, wherein the test signal is substantially less than a firing current used to activate the actuating assembly.

9. A power tool comprising:

a table;

a cutting tool supported in a way that extends above the table at an operator defined height during normal operation and can be moved under the table in response to a sensed condition;

an actuating assembly configured to force the cutting tool under the table;

a control system configured to activate the actuating assembly in response to a sensed condition; and

a detection system configured to test the functionality of the actuating assembly without activating the actuating assembly.

10. The power tool ofclaim 9, wherein the control system is configured such that power is not provided to a motor of the table saw when the detection system outputs a signal indicating that the actuating assembly is not functional.

11. The power tool ofclaim 9, wherein:

the actuating assembly includes a pyrotechnic module;

the detection system includes a comparator block;

the comparator block is configured to generate a first output when the pyrotechnic module is installed in the actuating assembly;

the comparator block is configured to generate a second output when the pyrotechnic module acts as an open or is not installed in the actuating assembly;

the comparator block is configured to generate a third output when the pyrotechnic module acts as a short in the actuating assembly; and

each of the first output, the second output, and the third output is different from the other of the first output, the second output, and the third output.

12. The power tool ofclaim 11, wherein the comparator block comprises:

a first comparator;

a first voltage reference operably connected to the first comparator;

a second comparator; and

a second voltage reference operably connected to the second comparator.

13. The power tool ofclaim 12, wherein:

the first voltage reference is configured to apply a first reference signal to a first input of the first comparator which is less than the expected lowest signal applied to a second input of the first comparator when the pyrotechnic module is positioned within the actuating assembly and a test signal is applied to the pyrotechnic module; and

the second voltage reference is configured to apply a second reference signal to a first input of the second comparator which is greater than the expected highest signal applied to a second input of the second comparator when the pyrotechnic module is positioned within the actuating assembly and the test signal is applied to the pyrotechnic module.

14. The power tool ofclaim 12, further comprising:

a receptacle configured to receive the pyrotechnic module; and

a differential amplifier block configured to detect a voltage difference across the receptacle when the test signal is applied to the receptacle, the differential amplifier block including an output operably connected to a first input of the first comparator and a first input of the second comparator.

15. The power tool ofclaim 14, further comprising:

a switch element having an input operably connected to a power supply and an output operably connected to the receptacle; and

a controller operably connected to an output of the first comparator and an output of the second comparator, the controller operably connected to the switch element for selectively operably connecting the power supply to the receptacle through the switch element.

16. The power tool ofclaim 15, wherein the test signal is substantially less than a firing current used to activate the actuating assembly.

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