Measurement System for Hand Tools

This invention relates to a system for measuring forces exerted by a hand tool when it is used by a worker.

Many occupations require repetitive hand motion and/or repetitive use of hand tools, such as pliers, knives, screwdrivers, and cutting snips. Recently, there has been significant attention to, and increased reporting of, cumulative trauma disorders (CTD's) which may be related to such repetitive hand motion. One CTD, for example, is carpal tunnel syndrome. This syndrome includes swelling of the median nerve, or thickening of the carpal ligament in the hand. The physiology of this syndrome is described in more detail in U.S. Pat. No. 4,774,966.

Diagnostic devices have been developed for testing forces exerted by the hand. These devices include, for example, a carpal tunnel syndrome screening device, U.S. Pat. No. 4,774,966; a grip rate measurement, U.S. Pat. No. 4,949,729; and a human hand load sensor, U.S. Pat. No. 5,125,270. The devices in these patents are specially designed test pieces of equipment for measuring forces by the hand of a person. Since these pieces of equipment are not similar to workplace tools, the tests do not provide data which reflects conditions which are encountered by a worker in a working environment. These devices typically test controlled individual movements over a short period of time, but do not provide information regarding extended repetitive use which is more typical of the workplace.

According to the present invention, a measurement system measures forces exerted by a tool, and, may additionally measure positions of a worker's hand when a hand tool is used, acceleration of the hand or tool, and angular movement of the tool. These measurements can be used to detect force characteristics of tools and tasks that may have a high risk associated with cumulative trauma injuries, to instruct workers on preferred methods for using the tools, to detect forces for rehabilitation of an injured worker, to redesign the tool, and/or to redesign the task for which the tool is used.

The hand tools are instrumented to provide force-related information which is relevant to the individual tool. Preferably, the instrumented tools have substantially the same weight, weight distribution, size, shape, surface texture, and feel of a non-instrumented tool which is normally used by a worker in the work environment. A number of different types of instrumented tools can be employed, such as a pair of pliers, a boning knife, a screwdriver, textile snips, and a wrench. The tools each have one or more sensors which detect force, torque, acceleration, linear position, and/or angular position. These sensors may include foil strain gages, accelerometers, linear displacement transducers, and potentiometers. (The term "force" is used herein not only to refer strictly to the product of mass and acceleration, but also may collectively refer to other force-related measurements, including torque and acceleration.)

A data collector is coupled to a tool to collect, process, and display data. The sensors in the tools provide analog voltage signals through an adapter which has pins. These pins mate with openings in a receptacle which is preferably mounted on the data collector housing. For each type of tool, preferably a group of pins provide an identification code which is unique to the type of tool. The identification code may be based on selectively short-ciruiting and open-circuiting certain pins reserved for identification purposes. The data collector has a processor which recognizes the type of tool from the identification code and accesses a stored program to determine parameters that are used for data processing and display. The parameters include conversion numbers for converting an input signal from a sensor to an output in selected units of measurement, such as units of force or acceleration. Where there are multiple sensors, the data collector may convert some signals to one type of units, and other signals to other units. The data collector periodically checks to determine whether the tool has been replaced with another type of tool.

The data collector can collect and display data in a number of different modes, including a real time mode, an average mode, and a task analysis mode. In the task analysis mode, the processor collects data, stores it in memory for a desired collection time, and post-processes the stored data. The stored data can also be downloaded to another computer for long term storage and further analysis. A user can thus compare data collected at one time with data collected at another. This ability to compare data collected at different times is useful, for example, to compare tools or tasks when changes are made.

As part of the post-processing, the data collector determines how many repetitions were made and when they were made with the tool during the time that data is collected and stored. To determine the number of repetitions, the processor uses rules which are specific to each type of tool, the rules being determined in response to the identification code. The rules include threshold parameters, such as the magnitude of the change in force versus time, to determine when a repetition has occurred. The processor calculates information to be displayed from the stored data including number of repetitions; average and peak force for each repetition and for the selected time period; and the duration of forceful exertion for each repetition and for all repetitions.

Other detectors can also be employed on the tool or on the hand of a worker. A position detector may be positioned on the hand for detecting hand or wrist position while using the tool, or it can be incorporated on the tool itself. Some tools, such as a knife, may be instrumented with an accelerometer on the handle for measuring the acceleration as the tool is used. The accelerometer can, for example, be mounted on a handle of the tool. Tools may be equipped to provide a measure of angular rotation. In the case of the pliers, for example, a potentiometer may be coupled to the fulcrum to indicate the relative position of the plier handles during forceful exertions.

Each of these detectors--position, accelerometer, or angular position--can provide a signal which is synchronized with the force-related signals. By observing the synchronized signals, a user can determine relationships between the forces exerted by the tool and the position, acceleration, and/or angular position. This information can be useful in redesigning tools and/or tasks to reduce the forces exerted by the tool.

According to the present invention, the measurement system allows a user to measure a force exerted by a tool in a worker's hand in the worker's actual working environment. The instrumented tools have substantially the same weight, weight distribution, feel, size, shape, and surface texture of a tool which is actually used in the work place. Consequently, the measurements accurately reflect forces in a work environment without requiring the worker to perform movements which would otherwise be needed to compensate for variations between an instrumented tool and an actual tool.

Other features and advantages will become apparent from the following detailed description when read in conjunction with the following figures in which:

FIG. 1 is a perspective view of an instrumented tool and a data collector according to the present invention;

FIGS. 2(a)-2(c) are perspectives view of a number of instrumented tools according to the present invention;

FIGS. 2(d)-2(e) are perspective views of other test devices which may be used for measuring forces;

FIG. 3 is a perspective view of the data collector;

FIG. 4 is an end view of an adapter;

FIG. 5 is a block diagram of the control system of the data collector according to the present invention; and

FIGS. 6-10 are flow charts of operation of the data collector according to the present invention; and

FIG. 11 is a graph illustrating a signal and slope thresholds.

According to the present invention, a measurement system is provided for measuring forces exerted by a hand tool when the hand tool is used by a worker. The tools are instrumented so that they simulate tools which are used by workers in actual practice. The system can measure force, torque, acceleration, position, and/or angular rotation of the tool, and position and/or acceleration of the hand. A data collector can process and display interpreted results conveniently for a user.

Referring to FIG. 1, a person 10 holds an instrumented tool 12 in hand 14. Tool 12 is a pair of pliers which has two handles 16 which are pivotally connected around fulcrum 18. Sensors 46, 49 (FIG. 2) are provided on the tool to measure torque exerted by hand 14 when handles 16 are compressed, and an angle of movement of the pliers, respectively. The sensors provide analog voltage signals over cable 20 to data collector 22. The data collector is coupled to cable 20 through an adapter 24.

A position sensor 26 is mounted on hand 14 and provides a position signal over cable 28. Cable 28 can be combined with cable 20 to provide the position signal synchronized with the other signals from sensors 46, 49. (In this description, "cable" typically refers to a number of wires.) The position sensor is typically a linear voltage transducer or potentiometer which is first zeroed in an anatomically neutral position. The transducer then provides a signal indicating change in position.

Referring to FIGS. 2(a)-2(c), a number of different instrumented work tools can be employed for measurement. Each of these tools is a version of an actual tool which has been instrumented to have one or more sensors for providing signals indicating force, torque, acceleration, position, and/or angular movement. The types of sensors which are used will vary depending on which measurements are relevant for the particular type of tool. Other types of tools, such as wrenches or textile snips, could also be similarly instrumented. Preferably, the instrumented versions of the tools have substantially the same weight, weight distribution, feel, surface texture, size, and shape as a tool which is used in the workplace. Such instrumentation allows a user to get the best possible field measurement, since the worker does not perform compensatory movements for differences between the instrumented tool and the workplace tool. A pair of pliers 30, shown in FIG. 2(a), has two handles 34, 38 which are brought together and rotate about a fulcrum. A sensor 46 has two foil strain gages mounted on each side of handle 34. The strain gages are incorporated in a full Wheatstone bridge circuit (not shown). Sensor 46 thus provides an analog voltage signal over cable 48 representative of the total torque about the fulcrum. An angle sensing potentiometer 45 is positioned at fulcrum 44 for measuring the relative rotation of the handles at the fulcrum. The potentiometer provides over a cable 49 an analog voltage signal which is related to the angular position. Cables 47, 48 each pass through a channel (not shown) in the handle so that they do not interfere with the worker using the pliers. While the cables are shown schematically in FIG. 2(a) for simplicity, it should be understood that they are preferably channelled in the pliers so that they appear, on visual inspection, only to enter handle 34 at an end 49. In one embodiment of a pair of pliers, metal springs 32, 36 are located on the inside of handles 34, 38. These springs each have a curved end portion 40, 42 near a fulcrum 44 which is compresses when the handles are brought together. With such springs, the sensor should be between the springs and the fulcrum. Other tools which operate in a similar manner, such as a textile snip or cutting shears, could be similarly instrumented.

A boning knife 50, shown in FIG. 2(b), has a handle 52 and a blade 54. Sensors 56, 58 are mounted on the handle 54 to measure the deflection of the handle in two orthogonal directions. Sensor 58 detects positive and negative bending in the direction of cutting, while sensor 56 measures bending which is transverse to the cutting direction. Each sensor 56, 58 has four strain gages which are wired into a full Wheatstone bridge circuit (not shown), and four wires for providing signals. A grip sensor 60 includes a foil strain gage which is mounted in the handle to detect force of the grip exerted by the handle when the tool is used by a worker. An accelerometer 64 is also coupled to the handle and provides a signal. Signals from all of these sensors are provided over cables which are collectively indicated as 62. The cables are preferably channeled through the knife handle and extend out of the base 68 of the handle so that the cables are not visible except at the base and do not interfere with a worker's operation of the knife.

The grip sensor could, alternatively be mounted on the exterior of the handle and could include a force sensitive resistor, or ultrasound force measurement sheets.

A multi-tool assembly 70, shown in FIG. 2(c), has a handle 72 which has an adapter 74 mounted longitudinally in the center of the handle. At the end of adapter 74 is a receptacle 76 to which a number of different attachments, such as nut driver 78, screwdriver 80, phillips head 82, and allen spline 84, can be removably coupled. Adapter 74 is rigidly coupled to the handle at one end 86, while over most of the length of the adapter, there is a small space 88 between handle 72 and adapter 74. Sensor 90 has foil strain gages which are incorporated in a full Wheatstone bridge circuit (not shown), and which are mounted on the adapter. Since adapter 74 is only rigidly coupled at one end, when a user rotates the handle to operate the nutdriver or screwdriver, a rotational deflection can be detected between adapter 74 and handle 72. A voltage signal proportional to the deflection is provided over cable 92. Attachments 78-84 are removable to allow more flexibility. Alternatively, an instrumented tool, such as a screwdriver, could be made without removable attachments.

A position sensor 94 also can be provided with each tool. By processing this signal, a velocity or acceleration can be determined by taking derivatives. For more accurate measurements, however, it is preferable to use an accelerometer which is typically mounted on the tool or on the hand for determining acceleration. Grip sensors can be provided in other tools when appropriate. For sensors with a Wheatstone bridge, a 5 volt regulated supply is provided from the data collector.

Other devices, shown in FIGS. 2(d)-2(e), can be used to measure force exerted on a tool, and can be packaged in a measurement kit with the instrumented tools shown in FIGS. 2(a)-2(c). Referring to FIG. 2(d), a generally box-shaped force transducer 120 has two threaded openings 122, 124 on opposite faces. These openings receive attachments such as a handle 126 at one end and a loop 128 at the other. Loop 128 can be connected on one of a number of further attachments, such as an alligator clip assembly 130 which has a hook 132 at one end for engaging the loop and a springed, toothed end 134 for clamping an object. Depending on the measurement need, a different attachment can be provided, such as other clamps, hooks, or straps. The transducer can be used to measure force exerted by other devices, such as handles, levers, knobs, or dials which must be used by workers. The transducer provides a signal over cable 136. Such transducers are available, for example, from HBM, Inc. of Marlboro, Mass.

Referring to FIG. 2(e), a pinch gage 140 is a dynamometer which has two plates 142, 144 which are connected with a spring (not shown). The pinch gage and the transducer in FIG. 2(d) may each be a stand-alone devices which include their own visible output mechanism (not shown) for receiving the signals and for providing an indication of the force exerted by the gage. A larger or differently configured pinch gage can also be used to measure hand grip.

A pinch gage can be used as a substitute for specific tools which have not been instrumented, or can be used for comparative tests with instrumented tools. A worker can be instructed to use the pinch gage to apply a similar force to the force which is normally applied by the worker in a work activity. Thus, simulated results can be obtained. If instrumented tools are available, it may also be useful to compare the estimated force of operation with the actual force determined by the instrumented tool.

Referring again to FIGS. 2(a)-2(c), pliers 30, knife 50, and multi-tool assembly 70 have adapters 97, 98, and 99, respectively, for coupling the signals from the sensors to a series of pins. Referring also to FIG. 4, the adapters are very similar to each other in size and outward appearance, and each has sixteen pins 102. The pins are different, however, depending on the tool. A group 104 of four pins in each adapter are reserved to provide a digital identification code, and thus up to sixteen different types of tools can be identified. The code is determined by selectively short-circuiting and open-circuiting pins. The pins are coupled to pins (not shown) of a processor (FIG. 5) when the adapter is plugged into a mating receptacle on the data collector. Thus a high or low voltage at each of the four processor pins indicates the code, and thus the type of tool. The remaining twelve pins of the adapter are connected to the various sensors to provide analog data to data collector 22. Some pins may be used to provide a voltage signal to the sensor-, such as a regulated five volt supply voltage for the strain gages in the Wheatstone bridge.

In other embodiments, the number of pins and their allocation between data collection from sensors and identification data could be varied as needed. Thus one could collect more data by expanding the data pins, and increase or decrease the number of different types of tools.

Referring to FIG. 3, data collector 22 has a receptacle 100 mounted on the housing 101 for receiving and mating with an adapter. A user interface on the data collector includes a keypad 110 and a liquid crystal display 112. The keypad, which is environmentally sealed, allows the user to enter data or to select a mode of operation for the data collector. The liquid crystal display provides easily readable data to a user. Data collector 22 is light-weight, portable, and hand-held, and is preferably powered with rechargeable batteries. In an exemplary embodiment, the data collector weighs less than two pounds, and measures 7.5.times.3.5.times.1.5 (in inches). Switch 106 is an on/off switch. Input port 108 includes a terminal for recharging the battery, and a terminal for downloading stored data to, and for uploading programming data from an external computer (not shown).

A block diagram of the circuitry and control system of the data collector of the present invention is shown in FIG. 5. Sensors 151 on an instrumented tool 150, a position detector 152, and an accelerometer 154 provide analog data to data collector 156. The data collector has a 12-bit analog-to-digital converter 156 which receives the analog data .and provides digital data 158 to a processor 160.

Tool 150 also provides digital identification data 162 via the pin configuration of the adapter through a digital I/O 164 to the processor. The processor receives identification data from tool 150, digital data 158 from converter 156, and user inputs from keypad 168, performs calculations, and provides output signals to a liquid crystal display 166. The form of the data which is presented to the user is determined by the user through inputs on keypad 168. A serial I/O interface 176 allows a user to download stored data from the memory to a computer, or to reprogram the processor when new tools or analytical functions are added.

Different instrumented tools have different requirements for performing calculations and presenting data. Some tools, such as the pliers, measure one force (compression) in one direction. Other tools, however, such as the knife, may measure two or more different forces, each of which may be in more than one direction (and thus defined as positive and negative). Consequently, calibration factors and units will be different, depending on the type of tool used.

When a tool is coupled to the data collector, the digital identification 170 received by processor 160 through the pin arrangement of the adapter causes the processor to access a program which is written into the processor. The program includes various parameters for each type of tool. The processor thus can retrieve the appropriate parameters relating to the particular type of tool. The processor causes the name of the tool to be indicated on the display. Periodically, the processor checks to determine whether a new tool has been coupled to the data collector.

These parameters include slope thresholds for determining repetitions (discussed below) and parameters for converting the input signals from the sensors to meaningful output signals. Analog data, typically received in millivolts, is converted to digital data 158 and can be represented numerically as counts in a predetermined range. The counts are a non-calibrated magnitude of the input signal over time. For each tool, a conversion factor in terms of counts/unit indicates a relationship between counts and the characteristic detected by the sensor, such as force-related units, such as pounds or foot-pounds, degrees of angular rotation, or units of position.

Flow charts in FIGS. 6-9 illustrate the processes used by the processor in response to user-selected modes of operation. As described above, when the tool is coupled to the data collector (step 200), the processor determines the type of tool from the digital identification (step 202), and retrieves appropriate parameters (step 204) for the particular type of tool from the stored program. The processor next determines whether a user has entered a particular mode of operation (step 206).

Referring to FIG. 7, if a real time mode is entered (step 210), the processor causes the display to indicate real time data such as real time force, peak force, angular position, and the time (step 212). Referring to FIG. 8, if average mode is entered (step 216), the processor directs the display to show averaged values, such as average force and peak force (step 218) over the time that the force is measured. The time can be either from the start time or from a later time which is designated as the beginning time for averaging purposes.

Referring to FIG. 9, if task analysis mode is selected and entered by the user (step 224), the processor prompts the user to indicate when to begin data collection, and waits until the user indicates when to start by pressing a start key (not shown) on the keypad (step 226). The user allows a worker to operate the instrumented tool as he or she would in a normal working environment over a normal number of repetitions with the tool, e.g., a number of compressions with the pliers or a number of cuts with the knife. The processor collects and stores the digitized data in memory (step 228) until the user indicates that the processor should stop storing data by pressing a stop key (not shown) on the keypad. A stop signal is received by the processor (step 230), and the processor begins post-processing the stored data. If a maximum time for data collection is exceeded, the data collector can stop data collection or can overwrite the data previously stored in memory starting at the first data set stored, or a signal can be provided to the user indicating the end of available storage.

The processor determines the number of repetitions which have occurred by analyzing the signal after the signal has been stored (step 231). Different techniques may be used for determining repetitions, depending on the type of tool which is used. The appropriate technique is known to the processor when the threshold parameters are accessed in the stored program in response to the identification signal for the type of tool.

An example of the determination of repetitions is illustrated in connection with FIG. 11. If the tool being used is a pair of pliers, for example, the processor checks signal 240 (which indicates a force versus time from the strain gage) for an upward slope 242 having a magnitude exceeding a predetermined threshold slope, followed by a downward slope 244 having a magnitude exceeding a predetermined threshold slope, followed by another upward slope 246 having a magnitude exceeding a predetermined threshold slope. When these slopes are detected, the processor determines that a positive repetition has occurred between the first upward slope and the first downward slope. The determination may also be based on a minimum time period over which the slope is calculated and/or a minimum threshold for the magnitude of the force. Since the processed data is digital, the time may be expressed as number of samples, where each unit represents the sample time of the analog-to-digital converter.

The sensor in a pair of pliers has only positive repetitions because the sensor only detects compression. In input signals from sensors in other tools, such as the knife, the forces may be in two directions, so positive and negative repetitions are determined. In addition to detecting a positive repetition which has a pattern of slopes which are upward, downward, and upward, the processor may additionally detect sequences of slopes which are downward, upward, and downward, thus indicating a negative repetition.

For different types of tools, the rules may be different, or may involve different types of repetitions. In the case of the knife, for example, a number of positive and negative repetitions may be determined separately for the sensor which measures force in the cutting direction, and for the sensor which measures force transverse to the cutting direction. Thus the processor determines four different numbers of repetitions, and these four numbers of repetitions may be different from each other. Another possibility for determining repetitions is to have rules used in combination, e.g., one signal must vary by one threshold, while another signal must vary by another threshold.

After determining the location and number of repetitions in the input signals, the processor provides calculated data, such as average force, peak force, and time, for each repetition and for the overall sample time, on the display (step 234). In one preferred embodiment, the processor automatically causes the display to show the number of repetitions, the frequency of repetitions, the duration of each repetition, the aggregate duration of all forceful exertions, and the overall time on an initial screen display. By pressing a key, a user can then access other data relating to average force, average peak force, and maximum peak force for the repetitions. These readings may be obtained both for positive and negative repetitions, and for each of a number of sensors.

FIG. 10 is a flowchart illustrating another mode of operation of the present invention in which a user selects a counter mode rather than a tool mode (step 250). When this mode is selected, the data collector serves as a counter which displays a number of user-entered occurrences, a time, and a frequency of occurrences. First, the data collecting time begins when a key on the data collector is entered (step 252). A user observes a worker doing a certain repetitive task and presses a key each time the user observes the worker doing one task, and another key when the user observes another task. The data collector receives the data, displays the time and number of occurrences in real time, and provides the frequency of occurrences on the display to the user (step 254). This feature is employed without a tool coupled to the data collector. When set mode is received (step 256), the data collector returns to its original mode.

By using the task analysis mode, a user can collect and process data for a worker in the actual working environment with a tool which simulates as close as possible the weight and feel of a tool actually used. These measurements enable testing of different tools for the least amount of harmful exerted force and number of repetitions, and allow testing of workers for potential health risks. Furthermore, a user can use this information to help determine whether it would be beneficial to redesign the tool, redesign the task, or improve workplace layout.

Having described an embodiment of the present invention, it should be apparent that other variations and modifications may be made to the present invention without departing from the scope of the invention as defined by the appended claims.

For example, in another embodiment, a handle with strain gages could be mounted in parallel to a handle of a tool. The parallel handle could be used to measure torques due to tasks such as painting with a brush or applying spackle. A strain gage would be coupled to the handle. This allows the instrumented tool to serve as a flexible multi-tool attachment. It would be difficult, however, to precisely simulate the weight and weight distribution with a parallel handle.