CN101588672A - Output protection circuit of Marx trigger of double-electrode gas switch - Google Patents

Output protection circuit of Marx trigger of double-electrode gas switch Download PDF

Info

Publication number
CN101588672A
CN101588672A CN 200910022925 CN200910022925A CN101588672A CN 101588672 A CN101588672 A CN 101588672A CN 200910022925 CN200910022925 CN 200910022925 CN 200910022925 A CN200910022925 A CN 200910022925A CN 101588672 A CN101588672 A CN 101588672A
Authority
CN
China
Prior art keywords
electrode gas
trigger
marx
marx trigger
capacitance
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
CN 200910022925
Other languages
Chinese (zh)
Other versions
CN101588672B (en
Inventor
杨兰均
杜修明
陈立
刘鹏
童金禄
袁均祥
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Xi'an Xijiao Ruili Electric Research Institute Co., Ltd.
Original Assignee
Xian Jiaotong University
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Xian Jiaotong University filed Critical Xian Jiaotong University
Priority to CN 200910022925 priority Critical patent/CN101588672B/en
Publication of CN101588672A publication Critical patent/CN101588672A/en
Application granted granted Critical
Publication of CN101588672B publication Critical patent/CN101588672B/en
Active legal-status Critical Current
Anticipated expiration legal-status Critical

Links

Images

Landscapes

  • Generation Of Surge Voltage And Current (AREA)

Abstract

The invention relates to a xenon lamp pumping primary power supply of a high-power solid laser and discloses an output protection circuit of a Marx trigger of a double-electrode gas switch for use in the xenon lamp pumping primary power supply of the high-power solid laser. The output protection circuit comprises a leak resistor, a stopping condenser and a discharge gap, wherein the stopping condenser and the discharge gap are serially connected between the output end of the Marx trigger and the cathode terminal of the double-electrode gas switch; and one end of the leak resistor is connected with the common node of the stopping condenser and the discharge gap, and the other end of the leak resistor is connected with the other end of the stopping condenser or directly grounded. The output protection circuit mainly solves the problem of isolation between a pulse voltage of a xenon lamp preionization circuit and the Marx trigger for triggering the double-electrode gas switch of a main discharge circuit when a high-power xenon flash lamp is driven, ensures the mutual normal cooperation between the triggering of the double-electrode gas switch of the main discharge circuit of the high-power xenon flash lamp and the preionization of the xenon lamp, and makes the operation of the xenon flash lamp reliable.

Description

A kind of output protection circuit of Marx trigger of two electrode gas switches
Technical field
The present invention relates to the primary source of great-power solid laser xenon flash lamp pumping, the output protection circuit of the Marx trigger of two electrode gas switches in particularly a kind of primary source that is applied to the great-power solid laser xenon flash lamp pumping.
Background technology
In the primary source system of light laser xenon flash lamp pumping, switch is responsible for energy is delivered to the load of highpowerpulse xenon lamp from energy-storage system, is the critical component of whole primary source system.The switch of extensive use at present is an ignitron, but along with of the development of light laser primary source system to bigger energy storage, the through-current capability of ignitron can't satisfy the demands, and the self breakdown probability is bigger, has been not suitable for the high reliability request of the primary source system of bigger energy storage to switch.
Two electrode gas switches have that through-current capability is strong, life-span length, working stability, the advantage that do not have heavy metal Hg to pollute.Two electrode gas switches need the electrode gap of the steep trigger impulse voltage breakdown gas switch of an amplitude height, forward position to make switch conduction in the course of the work.
When big electric current passes through xenon flash lamp, in order to prevent owing to the too fast xenon lamp that causes of electric current climbing speed is damaged, need to adopt a preionization pulse voltage to puncture the long gas gap of xenon flash lamp earlier, in xenon flash lamp, produce the plasma that high electricity is led, for the big pulse current after the hundreds of microsecond is got ready, after increasing the preionization process, reliability and the life-span of xenon flash lamp by big electric current the time is improved, if there is not the preionization process on the other hand, there is the conducting time-delay in xenon flash lamp, after increasing the preionization process, the conducting time-delay of xenon flash lamp exists hardly, the plasma that preionization produces makes the xenon flash lamp after discharge stable, and the synchronism of many xenon flash lamp discharges strengthens, and has improved the efficient of laser amplifier.Figure 1 shows that the common circuit of the two electrode gas switch great-power solid laser primary sources that do not adopt preionization technique, wherein the Marx trigger is as the trigger of two electrode gas switch ignition conductings.
Adopt preionization technique can improve the reliability and the life-span of the work of highpowerpulse xenon lamp greatly; if but under the effect of preionization pulse, do not take quarantine measures; as shown in Figure 1; be the power supply that produces the preionization pulse in the empty frame; after increasing the preionization pulse; because the preionization pulse is about an amplitude 40kV; other positive pulse of rising front us level; to act directly on Marx trigger output; Marx flip-flop circuit figure as shown in Figure 2; fill the 13kV left and right sides forward dc high pressure during its operate as normal; after capacitance is passed through in positive preionization pulse; because capacitance voltage can not suddenly change; the above high-voltage pulse of 50kV is born and directly puncture with instantaneous in afterbody ball crack; ball crack reverse sequence puncture successively in like manner; to misoperation occur behind the fast Marx generator of the high pressure reverse-conducting and export high-voltage pulse; cause two electrode gas switches by false triggering; thereby make preionization pulse and major loop pulse be added on the xenon flash lamp simultaneously; xenon flash lamp must explode; therefore must take to isolate accordingly the protective circuit of preionization pulse; to guarantee that two electrode gas switch triggering processes normally cooperate mutually with the preionization process of xenon flash lamp; just increase the time of delay of main discharge to the preionization pulse; make when the conducting of main discharge gas switch; the highpowerpulse xenon lamp is still kept conducting; and the preionization switch has disconnected; preionization branch road capacitor can not be reversed the vibration of charging like this, the xenon flash lamp reliability service of big current drives.
Summary of the invention
At two electrode gas switches of the prior art MARX trigger misoperation and the not high problem of reliability that may occur in the course of the work; the object of the present invention is to provide a kind of output protection circuit of Marx trigger of two electrode gas switches; adopt this output protection circuit; can effectively preionization pulse and Marx trigger be isolated malfuncton probability that assurance MARX trigger is low and high functional reliability.
For reaching above purpose, the present invention takes following technical scheme to be achieved:
A kind of output protection circuit of Marx trigger of two electrode gas switches; it is characterized in that; comprise: bleeder resistance; be connected the capacitance and the discharging gap of the series connection between the cathode terminal of the output of Marx trigger and two electrode gas switches; one end of described bleeder resistance is connected the common node of isolation capacitance and discharging gap, and the other end is connected the other end or the direct ground connection of isolation capacitance.
Further improvement of the present invention is:
The other end of described capacitance is connected the cathode terminal of two electrode gas switches by resonant inductance, and the other end of discharging gap is connected the output of Marx trigger.
The other end of described discharging gap is connected the cathode terminal of two electrode gas switches by resonant inductance, and the other end of capacitance is connected the output of Marx trigger.
The output protection circuit of the Marx trigger of the present invention's two electrode gas switches compared with prior art has the following advantages:
1, adopt this Marx trigger to trigger the protective circuit of two electrode gas switches, can make the Marx trigger of main discharge circuit gas switch not be subjected to the influence of preionization pulse voltage and export high-voltage pulse by mistake, to guarantee that two electrode gas switch triggering conductings lag behind the preionization moment tens of xenon lamp constantly to the hundreds of microsecond, and the time length that lags behind is controllable, thereby guarantees the xenon flash lamp reliability service of big current drives;
2, connect a discharge resistance to ground between the external series gap of employing Marx trigger and the capacitance, the residual charge that the capacitance of can releasing at short notice stores, guaranteed that Marx trigger output pulse amplitude can not reduce, thereby guaranteed the light a fire reliability of two electrode gas switches of Marx trigger.
3, adopt Marx trigger low-pressure end to connect the common ground end, guarantee that the voltage of high pressure fast pulse trigger low-pressure end is zero, avoided influence high pressure fast pulse flip-flop operation stability with the shortest distance.Reduced the Marx trigger to electromagnetic interference intensity on every side.
4, the main storage capacitor equivalent capacity of the employing of this Marx trigger is about 500pf~2000pf, under the prerequisite that guarantees reliable triggering two electrode gas switches, adopt less main storage capacitor can effectively reduce the output energy, thereby reduce the Marx trigger electromagnetic interference intensity on every side; Choosing capacitance is about 500pf~2000pf, adopts less capacitance can absorb the output energy of more Marx trigger, thereby reduces the electromagnetic interference intensity that triggers the loop.
Description of drawings
The present invention is described in further detail below in conjunction with the drawings and the specific embodiments.
Fig. 1 is the common circuit figure of two electrode gas switch great-power solid laser primary energies.
Fig. 2 is the circuit theory diagrams of Marx trigger.
Fig. 3 is the application circuit with Marx trigger output protection circuit of a kind of two electrode gas switches of the present invention.
Fig. 4 is the structure chart of Marx trigger and output protection circuit among Fig. 3.
Fig. 5 is the application circuit with Marx trigger output protection circuit of another kind of two electrode gas switches of the present invention.
Fig. 6 is the structure chart of Marx trigger and output protection circuit among Fig. 5.
Among Fig. 1-Fig. 6: C2, capacitance; C3, coupling capacitance; L2, resonant inductance; R1, bleeder resistance; S, external series gap; G, common ground end; D, MARX trigger earth terminal; K, MARX trigger output sleeve pipe.
Embodiment
Embodiment 1
As shown in Figure 3, Figure 4, be the application circuit of Marx trigger output protection circuit with a kind of two electrode gas switches of the present invention.Be specially at Marx trigger output connect successively external series gap S, capacitance C2, resonant inductance L2, and be connected with the cathode terminal of two electrode gas switches; The bleeder resistance R1 that connects between the common node of capacitance and resonant inductance and the ground, bleeder resistance R1 must can hold the voltage pulse output of MARX trigger and any fault not occur; The Marx trigger has the loop of one's own by coupling capacitance C3.Coupling capacitance C3 is connected across between the earth terminal of gas switch anode and MARX trigger.Guaranteeing under the prerequisite of insulation distance the connection of the coupling capacitance C3 compactness of should trying one's best.MARX trigger integral body places in the closed metal cavity of a coaxial configuration, adopt the working gas of dry air as insulating gas and gap, external series gap, capacitance and bleeder resistance all place Marx trigger inside, the benefit of integrated design is like this: at first external series gap can utilize Marx trigger air pressure inside to satisfy insulating requirements, saves the trouble of at every turn inflating to external series gap; Secondly, volume is little, compact conformation.The earth terminal of MARX trigger is taken as and is guaranteeing under the condition of insulation distance on the nearest trigger shell of MARX trigger output.
After adopting the serial connection external series gap; make the Marx trigger not be subjected to the influence of preionization pulse voltage and mistake to export high-voltage pulse; thereby the two electrode gas switch triggering processes that guarantee normally cooperate mutually with the preionization process of xenon lamp; when capacitance can arrive at the trigger impulse of nanosecond; do not influence the amplitude and the steepness of trigger impulse; but behind switch conduction, the heavy current pulse of microsecond level is then separated by capacitance, thereby plays the effect of protection Marx trigger.Because it is very short to trigger the loop ON time, on capacitance, will leave the part residual charge, thereby reduced the service efficiency of Marx trigger, therefore, jumbo bleeder resistance of high value of output termination at capacitance arrives ground, when Marx trigger output high pressure fast pulse, do not influence the amplitude and the forward position of trigger impulse; When the Marx trigger was not worked, the residual charge on the capacitance can slowly discharge by bleeder resistance again, and was ready for work next time.The Marx trigger is through behind the foregoing circuit, being connected in series a resonant inductance L2 again is connected with the cathode terminal end of two electrode gas switches, the equivalent capacity of resonant inductance L2 and two electrode gas switches produces resonance, can improve the amplitude of Marx trigger output pulse, by selecting suitable resonant inductance L2, the amplitude of trigger impulse can be risen to original 1.5~1.7 times.By coupling capacitance C3 of cross-over connection between the earth terminal of MARX trigger and gas switch anode, and the earth terminal of MARX trigger connected common with the shortest distance, can effectively reduce the transient voltage amplitude that trigger impulse produces at Marx trigger low-pressure end place, reduce the Marx trigger electromagnetic interference intensity on every side.
The selection of parameter scope of output protection circuit is as follows: external series gap is inner to be non-uniform field slightly, its dc breakdown voltage is not greater than 50kV (being to be punctured by preionization to get final product), its pulse breakdown voltage is not more than 70~75kV (guaranteeing reliably to be punctured by the Marx trigger), and the inflation absolute pressure is 1~5Bar; It is 10M Ω~60M Ω that bleeder resistance is selected resistance, and capacity is 120W~200W; The low-inductive capacitor series connection that capacitance is 5400pF by four capacitances, the withstand voltage of each electric capacity is 40kV, it is the high-voltage conducting wires of 0.5~1m that resonant inductance is selected length, the withstand voltage 100~200kV of coupling capacitance, capacitance 0.5~10nf.
In the implementation column 1, bleeder resistance R1 also can be connected in parallel on the capacitance two ends, can bear the MARX trigger voltage pulse output except requiring it for the requirement of bleeder resistance, also requires it to have bigger capacity, resistance value is taken as 60~100M Ω, and capacity is 200W~400W.
Embodiment 2
As Fig. 5, shown in Figure 6, be the application circuit of Marx trigger output protection circuit with a kind of two electrode gas switches of the present invention.Physical circuit is: at connect the successively cathode terminal of capacitance, external series gap, resonant inductance and two electrode gas switches of the output of Marx trigger; Common node between capacitance and external series gap connects common by bleeder resistance; The Marx trigger has the loop of one's own by coupling capacitance C3.The MARX trigger still adopts the used structure of application example 1, just only capacitance is placed Marx trigger inside, external series gap and bleeder resistance are all external, and its advantage is that the Marx flip flop design is simple, cost reduces, and be convenient between external series gap and Marx trigger parameter adjustment with cooperate.
Capacitance protects Marx trigger internal circuit not to be subjected to the influence of the big electric current of energy resource system major loop when the major loop conducting, and resonant inductance can improve voltage magnitude on the external series gap by resonance before the external series gap conducting.After triggering is finished, bleeder resistance forms bleed-off circuit by the isolation resistance of Marx trigger low-pressure end, external series gap makes the Marx trigger not be subjected to the influence of preionization pulse voltage and exports high-voltage pulse by mistake, thereby the two electrode gas switch triggering processes that guarantee normally cooperate mutually with the preionization process of xenon lamp, prevent that again the preionization pulse from causing damage in Marx trigger reverse-conducting moment to high accuracy high voltage direct current generator and light-operated 10kV pulse trigger.
The parameter of output protection circuit is selected as follows: capacitance adopts low inductance ceramic capacitor three of capacitance 1750pf, withstand voltage 50kV and two strings to form; Bleeder resistance adopts about resistance 60M Ω; Resonant inductance is 0.5~1 meter high-voltage conducting wires; External series gap inflation absolute pressure 1~5bar, more than its self-breakdown voltage 50kV, pulse breakdown voltage is no more than 70kV; Withstand voltage 100~the 200kV of coupling capacitance, capacitance 0.5~10nf.
In the implementation column 2, bleeder resistance R1 also can be connected in parallel on the capacitance two ends, can bear the MARX trigger voltage pulse output except requiring it for the requirement of bleeder resistance, also requires it to have bigger capacity, resistance value is taken as 60~100M Ω, and capacity is for being 200W~400W.
Embodiment 3
The present embodiment circuit theory diagrams are with embodiment 1, but Marx trigger master storage capacitor parameter is from 20kV, and 10nf reduces to 20kV, 5nf, and the capacitance parameter is chosen as 1000pf, withstand voltage 200kV.
Because Marx trigger master storage capacitor reduces, after its output energy reduces, reduced electromagnetic interference amplitude to other equipment of energy resource system; After increasing capacitance, when the Marx trigger is exported, reduced noise amplitudes to circuits for triggering thereby absorb multipotency more.
The resonant inductance correspondence is reduced to the following high-voltage conducting wires of 0.4m in the present embodiment, and all the other output protection circuit parameter ranges of choice are with embodiment 1.
Embodiment 4
Present embodiment circuit theory diagrams and mounting structure be with embodiment 2, but Marx trigger master storage capacitor parameter is from 20Kv, and 10nf reduces to 20kV, and 6nf reduces to 500pf every straight equivalent capacity from 2625pf.
With embodiment 3, reduce main storage capacitor and capacitance after, can effectively reduce triggering the electromagnetic interference amplitude of loop and peripheral equipment.
Resonant inductance is the high-voltage conducting wires less than 0.4m in the present embodiment, and the capacitance capacitance adopts 2 withstand voltage 50kV, and electric capacity is that the low inductance ceramic capacitor of 1nf is in series, and all the other output protection circuit parameter ranges of choice are with embodiment 2.

Claims (3)

1, a kind of output protection circuit of Marx trigger of two electrode gas switches; it is characterized in that; comprise: bleeder resistance; be connected the capacitance and the discharging gap of the series connection between the cathode terminal of the output of Marx trigger and two electrode gas switches; one end of described bleeder resistance is connected the common node of isolation capacitance and discharging gap, and the other end is connected the other end or the direct ground connection of isolation capacitance.
2, the output protection circuit of the Marx trigger of a kind of two electrode gas switches according to claim 1; it is characterized in that; the other end of described capacitance is connected the cathode terminal of two electrode gas switches by resonant inductance, and the other end of discharging gap is connected the output of Marx trigger.
3, the output protection circuit of the Marx trigger of a kind of two electrode gas switches according to claim 1; it is characterized in that; the other end of described discharging gap is connected the cathode terminal of two electrode gas switches by resonant inductance, and the other end of capacitance is connected the output of Marx trigger.
CN 200910022925 2009-06-11 2009-06-11 Output protection circuit of Marx trigger of double-electrode gas switch Active CN101588672B (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CN 200910022925 CN101588672B (en) 2009-06-11 2009-06-11 Output protection circuit of Marx trigger of double-electrode gas switch

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CN 200910022925 CN101588672B (en) 2009-06-11 2009-06-11 Output protection circuit of Marx trigger of double-electrode gas switch

Publications (2)

Publication Number Publication Date
CN101588672A true CN101588672A (en) 2009-11-25
CN101588672B CN101588672B (en) 2013-01-02

Family

ID=41372660

Family Applications (1)

Application Number Title Priority Date Filing Date
CN 200910022925 Active CN101588672B (en) 2009-06-11 2009-06-11 Output protection circuit of Marx trigger of double-electrode gas switch

Country Status (1)

Country Link
CN (1) CN101588672B (en)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103023462A (en) * 2012-12-13 2013-04-03 西安电子工程研究所 Generator for generating exponential rise pulse current
CN105307367A (en) * 2015-09-14 2016-02-03 西安交通大学 Circuit used for prolonging service life of two-electrode gas switch and method
CN106849918A (en) * 2017-01-23 2017-06-13 华中科技大学 A kind of xenon lamp encourages the pulse pump supply unit of high-energy laser
CN107026384A (en) * 2017-05-02 2017-08-08 中国工程物理研究院激光聚变研究中心 A kind of xenon lamp device for solid laser amplifier pump energy
CN108390586A (en) * 2018-04-13 2018-08-10 武汉华中华昌能源电气科技有限公司 A kind of flash pumping laser power circuit
CN114421930A (en) * 2021-12-20 2022-04-29 西北核技术研究所 Marx generator based on photoconductive switch triggering and triggering circuit based on photoconductive switch

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5311067A (en) * 1992-06-15 1994-05-10 The United States Of America As Represented By The Secretary Of The Navy High performance pulse generator
CN201450658U (en) * 2009-06-11 2010-05-05 西安交通大学 Output protection circuit of Marx trigger of two-electrode gas switch

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103023462A (en) * 2012-12-13 2013-04-03 西安电子工程研究所 Generator for generating exponential rise pulse current
CN103023462B (en) * 2012-12-13 2015-02-04 西安电子工程研究所 Generator for generating exponential rise pulse current
CN105307367A (en) * 2015-09-14 2016-02-03 西安交通大学 Circuit used for prolonging service life of two-electrode gas switch and method
CN105307367B (en) * 2015-09-14 2018-07-17 西安交通大学 A kind of circuit and method extending two-electrode gas switch service life number
CN106849918A (en) * 2017-01-23 2017-06-13 华中科技大学 A kind of xenon lamp encourages the pulse pump supply unit of high-energy laser
CN106849918B (en) * 2017-01-23 2019-01-29 华中科技大学 A kind of pulse pump power supply device of xenon lamp excitation high-energy laser
CN107026384A (en) * 2017-05-02 2017-08-08 中国工程物理研究院激光聚变研究中心 A kind of xenon lamp device for solid laser amplifier pump energy
CN107026384B (en) * 2017-05-02 2023-07-21 中国工程物理研究院激光聚变研究中心 Xenon lamp device for pumping energy of solid laser amplifier
CN108390586A (en) * 2018-04-13 2018-08-10 武汉华中华昌能源电气科技有限公司 A kind of flash pumping laser power circuit
CN114421930A (en) * 2021-12-20 2022-04-29 西北核技术研究所 Marx generator based on photoconductive switch triggering and triggering circuit based on photoconductive switch

Also Published As

Publication number Publication date
CN101588672B (en) 2013-01-02

Similar Documents

Publication Publication Date Title
CN101588672B (en) Output protection circuit of Marx trigger of double-electrode gas switch
CN104467772B (en) Pulse transformer D-flip flop
CN101478139A (en) Multi-path large power velocity modulated valve overcurrent real-time protection apparatus having on-line self-detection function
CN103475255A (en) Marx generator with compact structure
CN201450658U (en) Output protection circuit of Marx trigger of two-electrode gas switch
CN103400717A (en) Multi-electrode field distortion gas switch and multi-switch synchronous triggering method
CN101715269B (en) Marx trigger for two-electrode gas switches
CN208016090U (en) A kind of pulse xenon lamp power source device of band triggering pre-burning device
Neuber et al. A compact, repetitive, 500kV, 500 J, Marx generator
CN103490662B (en) High-isolation high-voltage pulse power source
CN201550090U (en) Pulse modulator
CN201550347U (en) Marx trigger used for gas switch with two electrodes
CN208158967U (en) A kind of commutation switch device suitable for flexible DC transmission dc circuit breaker
CN103997252A (en) High-frequency and high-voltage pulse generation circuit
CN105372462A (en) Multi-waveform impact current generator
CN104244545A (en) Triggering pre-burning device with xenon lamp
CN109672358B (en) Nanosecond leading edge bipolar high-voltage pulse generation device
CN102355156A (en) Novel Marx pulse forming circuit
CN101841253A (en) Pulsed-liquid phase discharge system based on multiplex IGCT parallel connection
CN202309649U (en) Marx pulse forming circuit
CN115333397A (en) All-solid-state hundred-kilovolt high-voltage nanosecond pulse power supply
CN108322988A (en) A kind of commutation switch device suitable for flexible DC power transmission dc circuit breaker
CN103780119A (en) High-power and long-pulse power source
CN204465486U (en) A kind of coaxial type Marx generator
CN109004918A (en) A kind of subnanosecond high-voltage pulse generation circuit

Legal Events

Date Code Title Description
C06 Publication
PB01 Publication
C10 Entry into substantive examination
SE01 Entry into force of request for substantive examination
C14 Grant of patent or utility model
GR01 Patent grant
TR01 Transfer of patent right

Effective date of registration: 20180808

Address after: 710077 room 10607, block C, Xi'an National Digital publishing base, 996 high tech Zone, Xi an City, Shaanxi Province.

Patentee after: Xi'an Xijiao Ruili Electric Research Institute Co., Ltd.

Address before: 710049 28 Xianning Road, Beilin District, Xi'an, Shaanxi

Patentee before: Xi'an Jiaotong University

TR01 Transfer of patent right