Patent US3373355A successfully refreshed from Google Patents.
US4887499A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Power screwdriver with torque limiter
Assignee: Individual
•
Filing: 1988-09-28
•
Granted: 1989-12-19
•
Expires: 2008-09-28
Abstract
Abstract The instant invention relates to a power screwdriver with torque limiter, with a drive unit and a secondary transmission, with an output shaft for the attachment of a keyed bit. According to the invention the drive unit is a pneumatic motor (2) with a compressed-air intake (13) and a compressed-air outlet (14), whereby the differential pressure between the compressed-air intake (13) and the compressed-air outlet (14) (measuring circuits 19 and 20) is taken as the measure of the torque produced by the power screwdriver (1). The differential pressure is measured in a differential pressure measuring device (21) and the measure signal is transmitted to a control unit (23). The control unit (23) contains a comparator unit which compares the measured differential pressure signal with a set value of differential pressure (adjusting potentiometer 24) and transmits a switching signal to a switch unit (solenoid valve 19) to switch off the power screwdriver when the compared values become equal. In this manner a simple calculation of torque is achieved by means of a differential pressure measurement in combination with a simple switch-off possibility. In further embodiments the rotational speed of the pneumatic motor is usedr additionally in the determination of torque.
Inventors
- 👤 Albert Kipfelsberger
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-08 02:40
CPC Classifications
B; B25; B25B; B25B23/00; B25B23/14; B25B23/145; B25B23/0078
Claims Analysis
Total Claims: 16
Claim 1
Independent Claim
147 words
A power screwdriver having a torque limiter, a drive unit, and a secondary transmission coupled to said driving unit having an output shaft for the attachment of a keyed bit, characterized in that said drive unit includes a pneumatic motor having a compressed-air intake and a compressed-air outlet; a differential pressure measuring unit for measuring the pressure difference between said compressed-air intake and said compressed-air outlet as an indication of the torque produced by the power screwdriver; a comparator unit for comparing said measured pressure difference in the form of an actual pressure value with a preset pressure difference in the form of a set pressure value representing a preset torque value, said comparator unit having a switch output signal; and a switch unit for switching said power screwdriver off when said set value of differential pressure has been reached in response to said switch output signal.
Claim 2
Dependent Claim
147 words
A power screwdriver having a torque limiter, a drive unit, and a secondary transmission coupled to said driving unit having an output shaft for the attachment of a keyed bit, characterized in that said drive unit includes a pneumatic motor having a compressed-air intake and a compressed-air outlet; a differential pressure measuring unit for measuring the pressure difference between said compressed-air intake and said compressed-air outlet as an indication of the torque produced by the power screwdriver; a comparator unit for comparing said measured pressure difference in the form of an actual pressure value with a preset pressure difference in the form of a set pressure value representing a preset torque value, said comparator unit having a switch output signal; and a switch unit for switching said power screwdriver off when said set value of differential pressure has been reached in response to said switch output signal.
Claim 3
Dependent Claim
30 words
The device of claim 1 including air circuits connecting said compressed-air intake to operating spaces of said pneumatic motor, and connecting said compressed-air outlet to said differential pressure measuring unit.
Claim 4
Dependent Claim
25 words
The device of claim 1 wherein said comparator unit includes a setting scale calibrated in corresponding assigned torque values for setting said set pressure value.
Claim 5
Dependent Claim
25 words
The device of claim 1 wherein said differential pressure measuring unit includes a measuring transducer which converts the measured pressure difference into an electrical signal.
Claim 6
Dependent Claim
37 words
The device of claim 4 wherein said comparator unit includes means for electrically comparing said measured pressure values and said set pressure value, and said set pressure value can be preset in form of an electric signal.
Claim 7
Dependent Claim
26 words
The device of claim 5 including a linearization unit provided between said differential pressure measuring unit and said switch unit for providing a linearized switching signal.
Claim 8
Dependent Claim
18 words
The device of claim 1 wherein said switch unit includes a switching valve in said compressed-air intake circuit.
Claim 9
Dependent Claim
19 words
The device of claim 7 wherein said switching valve consists of a solenoid valve connected to the comparator unit.
Claim 10
Dependent Claim
42 words
The device of claim 7 wherein said switching valve includes a magnetic valve having an electric, bistable state capable of being triggered by switching impulses to an open position in a first state and to a closed position in a second state.
Claim 11
Dependent Claim
54 words
The device of claim 1 including a rotational speed unit for measuring the rotational speed of the pneumatic motor to provide a rotational speed signal which is additionally taken into consideration to determine the torque produced by the power screwdriver, said rotational speed signal and measured pressure difference signal are transmitted to switch unit.
Claim 12
Dependent Claim
21 words
The device of claim 10 including a combination circuit for transmitting said rotational speed signal and said measure pressure difference signal.
Claim 13
Dependent Claim
35 words
The device of claim 11 wherein said combination circuit multiplies the pressure difference signal by the period for one revolution of the pneumatic motor and generates a switching signal to switch off the power screwdriver.
Claim 14
Dependent Claim
35 words
The device of claim 10 wherein said rotation speed unit processes periodic amplitude changes in the differential pressure signal as a function of the rotational speed to determine the rotational speed of the pneumatic motor.
Claim 15
Dependent Claim
46 words
The device of claim 13 including impulses produced by said amplitude changes passing through a trigger threshold; a counter having a gating circuit, and a clock for counting said impulses to produce a counted value; and the counted value is measured to determine the rotational speed.
Claim 16
Dependent Claim
64 words
The device of claim 1 including a housing of the power screwdriver which contains all of the electrical elements which are cast in said housing as one piece thereby eliminating external control and regulating units so that all influences acting upon the calculation of torque are taken into account within the power screwdriver and the power screwdriver can be used in an explosion-protected area.
References Cited (Backward Citations)
DE2236697A1
Cited
GB1480894A
Cited
US3939920A
Cited
US4023627A
Cited
DE2600940A1
Cited
US4081037A
Cited
US4552041A
Cited
US4631992A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1992-12-18 | 1993-06-19 | 1993-12-19 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1996-12-18 | 1997-06-19 | 1997-12-19 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2000-12-18 | 2001-06-19 | 2001-12-19 | $7700.00 | Window Closed / Lapsed |