WO2003101322A1

WO2003101322A1 - Tool holder

Info

Publication number: WO2003101322A1
Application number: PCT/SE2003/000914
Authority: WO
Inventors: Bo Tillander; Ingemar Ivarsson; Lars Palm; Ingvar Karlsson
Original assignee: Bo Tillander; Ingemar Ivarsson; Lars Palm; Ingvar Karlsson
Priority date: 2002-06-03
Filing date: 2003-06-03
Publication date: 2003-12-11
Also published as: AU2003246205A1; EP1509149A1; SE0201688D0; SE524192C2; SE0201688L

Abstract

Present invention relates to a rotary tool holder comprising a holder for fixing a tool (6) and a moment defining and rotary detaching unit. The moment defining and rotary detaching unit comprises a magnetic based torque sensor (1), connected to a circuit that compares a first outgoing torque related signal with a second outgoing torque related, and/or produce a first and a second outgoing torque related signal. The tool holder is arranged to stop the rotation of the tool holder at a maximum achieved torque.

Description

TITLE

TOOL HOLDER

DESCRIPTION

TECHNICAL FIELD

The present invention relates to a rotary tool holder comprising a holder for fixing a tool and a moment defining/rotation releasing unit.

BACKGROUND AND THE PROBLEM

Each year in Sweden about 18 000 people meet with hip bone fractures and about 25 000 people with wrist fractures. Thigh-bone, knee, lower leg, ankle joint, upper arm, elbow, lower arm and finger fractures are examples of other rather common fractures. When treating these different types of fractures plates that are fixed with screws, marrow nails that are locked with screws or merely screws are used to attain good stability in the fracture and with that a successful healing result.

A large number of the patients consists of middle aged and older people with brittleness of the bones, so called osteoporosis. The bone tissue of patients with osteoporosis is thin and weak and therefore it is frequently ocurring that the bone parts, in the fracture, are splitted up and that the quality of the bone tissue makes it hard to get a good hold with the screws. The stability in the fracture is highly dependent on the tensile strength in the bone screws.

When the operater tightens the screws there is the risk to tighten the screws too hard/far, which makes the strength between screw and bone worse. It also easily happens that the screw is not tighten enough. Consequently it is always hard to decide if one thightens too little or too much. The only thing that guides the operator is the feeling in the hand in relation to the equipment, for example the screwdriver and it varies from patient to patient. For inexperienced operators this is a difficult factor and the risk of tightening the screw too little or too hard is immediate. This can be difficult to estimate for experienced operators as well, especially when dealing with osteoporosis fractures.

When stability is inadequate the fracture breaks down. This results in increased pain, function losses and re-operations at the risk of additional complications like postoperative infections, pneumonia and thrombosis (deep vein thromboses). This results in prolonged care periods and consequently the suffering for the patients and the costs for the medical treatment. Fracture operations performed daily at all orthopaedic clinics. About half of the total number of orthopaedic operations consists of emergency injuries that is fractures.

There are previously known motor driven screwdrivers for bone screws. In SE-C- 464 960 a motor driven screwdriver intended for bone screws being releasable at a predetermined torque value. The screwdriver comprises an electrical motor, a rotation speed gear reduction unit, and a screwing part. The screw driving part is either arranged at the power supply part of the engine or at the gear transmission.

In the first case the power supply circuit of the electrical engine may be switched off at said predetermined torque value. In the second case the screw driving part is connected to the rotation speed gear reduction, at a release part thereof, which part can be activated at said predetermined torque value.

WO 98/27886 describes a surgical instrument compπsing a tool to be used i.a., when screwing a bone screw. The insrtrument is thereby characterized in that it comprises a detection means. The detection means send off signals depending on torque and angle of the tool to a display unit, which comprises a computer unit. The angle grapg of the torque can be read and will then form the basis for determination of the quality of the bone tissue.

In GB 2,021,022 a measuring device is described for measuring the torque and the angle when screwing a bone screw.

None of said documents discloses a screw driver measuring the torque and which stops, or provide some type of signal allowing the operator to know when the torque between screw and bone is at its highest, alternatively. A device having these properties would increase the quality at the treatment of bone fractures, in particular in older patients having osteoporosis related fractures.

Screw drivers and drilling machines provided with torque sensors are not available within any field. Within industry screen couplings are used which makes the machine slide at overload. In many of the previously designed devices for measuring torque the consumption of current of the machine in relation to the turning angle is used, the screwed length, for calculating the torque. This is not accurate enough as a bad bone structure means that the screw rotates without moving forward. This means that the screwed length is incorrectly monitored which in turn leads to a destruction of the thread.

By means of the present invention the applicable and possible maximal torque related to the material in question always will be obtained. The invention is thereby general and can be applied on all types of material, from fragile biological tissue to a steel quality.

OBJECT OF THE INVENTION AND SOLUTION OF THE PROBLEM The object has been to solve the above mentioned problem by obtaining a rotating tool holder:

• which reads the torque characteristic independent of the size, length and diameter of the tool, and the structure of the material, bone structure and the like,

• in which standard components can be used, no specially designed or specially manufactured components will be needed,

• which accurately determines the load, and

• which can be used both within orthopaedics, fine mechanics, and precision operations.

This has been solved as the torque defining and releasing unit comprises a torque sensor, which for example may be magnetic flux based. The torque sensor is connected to a circuit which compares a first output torque related signal with a second output torque related signal, and which torque sensor further is arranged to stop the rotation of the tool holder when a maximal torque has been obtained.

BRIEF DESCRIPTION OF THE DRAWING

In the following the invention will be described more in detail by means of a number of embodiments and with reference to the attached drawing, wherein Fig.l schematically shows the rotating tool holder according to the invention and its ingoing parts seen in a lateral view, and

Fig.2 shows a schematic, illustrating torque characteristic according to the invention.

DESCRIPTION OF EMBODIMENT The invention comprises a torque sensor, such as FAST Technology, in a modified design, which will be denoted 1 in the drawing, a fixed coupling 2 comprising a wedge coupling or the similar, a planetary gear 3, an engine 4 of DC or AC type, respectively, a quick exchange chuck , a tool 6, which can be of different kinds, such as a drill, srew bit, honing tool, milling tool, or the similar and a switch 7.

The device according to the invention need not be driven by an engine but the torque sensor 1 can be connected to a hand driven tool holder as well.

The torque sensor 1 which is used in the invention is described in the documents WO 00/57150 and WO 00/58704. In WO 99/56099 there is further a device for the torque sensor described, and in WO 98/52063 there is described a circuit for the torque sensor. These patent specifications are hereby incorporated as references.

The circuit described in WO 98/52063 is similar to the circuit used in the present invention and will thus not be described in more detail herein. The torque sensor 1 according to the invention is a sensor using changes in electromagnetic flux in a material.

The circuit monitors a magnetic field generated and produces a signal, which is then compared with a previous signal. The signals are taken care of in an electrical control unit in the form of a control system, which in turn stops or presents a warning when the torque increases or decreases. The electrical control circuit used is a feedback control system built in such a smooth and minimal way as possible. The internal size of the signals determines the release of the rotating torque.

The torque sensor 1 possesses a very high accuracy and is sensitive determining the load. The load measurement is done as a torque determination. The load value is then is then fed back to the control system. The idea of the present invention is based on the fact that one place a magnetic code on the shaft of the torque sensor 1, between the chuck 5 and the planetary gear 3. The principle allows for wireless transmission between shaft and subsequent electronics system. The device determines the load on the driving shaft under very high speed which requires a fast and accurate measuring course. Determination of torque according to the invention provides very fast and accurate values and can be obtained a rotation speeds up to 100,000 rpm which is necessary when the operator in certain cases need to stop the tool 6 in fractions of a second. The invention is in particular designed for medical use where a great accuracy is required, but can also be used within other areas demanding great accuracy, such as for example in fine mechanics and precision technique.

The tool 6 can be a drill, a srew bit, a honing tool, a milling tool, or the similar rotating tool. The two main applications of the device of the invention is designed for is as follows:

1. At the screwing in of screws in different bone tissue structures in connection with orthopaedic surgery. Then there is a requirement for a control system that controls the strength of the bone tissue structure and when needed alarms or stops. If no alarm is given the screwing will continue until a set top value has been reached.

2. At the drilling of holes into which the screws are to be drawn as a connecting element betrween skeletal parts and reinforcement details. Even at this operation the drilling resistance is controlled and the device according to the invention alarms or stops when needed. When drilling through skeletal parts the torque decreases and the drill will be rapidly stopped to minimize damages upon underlying blood vessels, nerves and tissues.

The speed of the screw driver or drilling machine is variable, whereby the operator decides the speed. The rotational speed of the shaft of the engine is about 15 000- 16 000 rpm which is then geared up or down by means of a planetary transmission. The planetary transmission has a fixed down or up coupling selected at choice. The outgoing rotational speed depends of the choice of planetary transmission. The rotational speed may then be varied within the range of the actual planetary transmission.

The planetary transmission 3 of the present invention has a fixed gear reduction being controlled by the switch 7. At drilling a rotational speed of preferably 250 rpm is used and when drawing a screw a rotational speed of about 100 to 200 rpm is used. At drilling the number of rpm can be varied between about 10 to 250 rpm, which the operator controls by the switch 7. Different types of drills, screws and other tools can be used depending on the bone tissue. When it comes to screws cortial screws are used at normal/healthy bone tissue and spongeous screws are used at brittleness of bone, osteoporosis.

The torque defining and releasing unit comprises the torque sensor 1. The circuit to which the torque sensor 1 is connected compares a first outgoing torque related signal with a second outgoing torque related signal, and/or produces a first and second outgoing torque related signals.

The torque sensor 1 delivers a torque signal (v), which the computer unit reads at the time t₀. At the time point ti the computer unit reads a new signal, which the torque sensor delivers. The computer unit then compares the torque related signals, at t₀ and ti. As long as Δv is positive, which is denoted a in the drawing the instrument will be provided with a continued power supply, but as son as Δv becomes zero, which is denoted b in the drawing or when Δv becomes negative which is denoted c in the drawing, the power supply is disconnected. The computer unit reads continuously new torque values. When the t₀ and ti values have been read the torque values at ti and t₂ will be compared, t₂ and t₃ and so on. In this way the torque sensor 1 is arranged to stop the rotation of the tool holder at a maximally reached torque, thus when Δv is equal to zero, which is denoted b in the drawing. Thus it is considered that the power supply shall be disconnected immediately when Δv is equal to zero. If the characteristic becomes negative very fast and the registrations are not made often enough in such a way that the computer unit misses when Δv is equal to zero, the power supply will be disconnected when Δv is negative, which is denoted c in the drawing.

In a first embodying example the tool 6 stops immediately when the torque decreases, at a negative torque change, without need for observation or listening to an alarm signal and then act from there. When the tool stops, a signal or the similar, according to one embodiment, calls the attention of the operator of the fact. In a second embodying example the trouble warning system of the control system is activated when the torque decreases. The trouble warning system comprises an alarm unit, which alarm unit provides the operator with the possibility of considering the necessity to intervene. The alarm should be increasing relative to the divergence and be of the type sound, light, vibration, or the similar. The principle means that changes of torque provides a corresponding change of signal strength. A sound increases or decreases in volume, respectively, a clicking sound increases or decreases in frequency, respectively, and so on. An alarm may be provided in the form of a vibration, as well, a display on a computor screen, in the form of a light signal or the similar. The transmission can be made visually, using a summer, an ear-phone or a similar system.

There are a number of parameters influencing the calculation of the maximal torque being the basis for when the control system shall stop or release an alarm. In particular the pitch of the thread, the pitch of the tool (thread) in comparison with the number of rotations, the diameter and length of the tool, the material or quality, alternatively, of the bone tissue structure, different tensions in the material/bone tissue, the speed of the tool in relation to the pitch of the tool and the similar. For example, the torque demand of the present invention at the following screw diameters is: screw « φ 4mm, 80-120 Nm screw » φ 8mm, 2,4 Nm screw » φ 12mm, 4,5 Nm

The different torques depend i.a., on the time demand, that is to say how long time that is maximally allowed before the control system stops the tool or alarms the operator. This time can be defined in different ways.

According to one embodiment the longest time is defined, e.g., if the tool has to be stopped within a tenth of a second, or less, <. a tenth of a second.

According to a further embodiment the time is defined relative to the number of revolutions that are maximally accepted before the tool stops, e.g., a 1/4 revolution.

According to a further embodiment the time is defined according to a number of predetermined fixed positions, e.g., ten different digits are marked in one revolution, whereby the operator can set at which mark the tool is to stop and thus how fast the tool stops.

The present invention has now been disclosed by means of some embodying examples and it should be understood that different modifications and complementary additions can be made within the scope of the invention as defined in the accompanying claims.

Claims

1. Rotary tool holder comprising a holder for fixing a tool (6) and a torque defining and rotary detaching unit. characterised in that the torque defining and rotary detaching unit comprises a magnetic based torque sensor (1), connected to a circuit that compares a first outgoing torque related signal with a second outgoing torque related signal, and/or produces first and second outgoing torque related signals, and is arranged to stop the rotation of the tool holder at a maximum achieved torque.

2. Rotary tool holder of claim 1, characterised in that said tool (6) consists of a screwdriver.

3. Rotary tool holder of claim 1, characterised in that said tool (6) consists of a drill.

4. Rotary tool holder of claim 1, characterised in that said tool (6) consists of a grinder.

5. Rotary tool holder of claim 1, characterised in that said tool (6) consists of a cutter.

6. Rotary tool holder of claim 1, characterised in that said tool (6) is used in orthopaedics.

7. Rotary tool holder of claim 1, characterised in that said tool holder is manually operated, rotary arranged.

8. Rotary tool holder of claim 1, characterised in that said tool holder is motor-driven rotary arranged.

9. Rotary tool holder of claim 1, characterised in that said tool holder is arranged to wireless transmit said torque related signals between the axis and subsequent electronic circuit.

10. Computer unit for comparing a first signal and a second signal outgoing from the torque transmitter, according to claim 1-9, characterised in that said computer unit maintains or cuts the power supply depending on the result of the signal comparison.