Pneumatic grip systems and material testing systems including pneumatic grip systems

1. A material testing system, comprising:

a pneumatic grip configured to grip a specimen under test based on a supplied pressure; and

a processor configured to control the pressure supplied to the pneumatic grip during a pressurization of the pneumatic grip over a plurality of fill cycles by repeatedly:

in response to determining that a current pressure is less than a target pressure for the pressurization, performing one of the plurality of fill cycles by controlling a fill valve to increase the supplied pressure;

allowing the supplied pressure to stabilize by switching the fill valve to a hold state for a wait time after the fill cycle; and

adjusting the wait time based on comparing an expected pressure increase to an actual pressure increase during a prior one of the fill cycles.

2. The material test system as defined in claim 1 , wherein the pneumatic grip comprises a first grip and a second grip, and the processor is configured to control the pressure supplied to the pneumatic grip by controlling the pressure to at least one of the first grip or the second grip.

3. The material test system as defined in claim 2 , further comprising a second fill valve, wherein the fill valve is configured to control gas flow from a gas supply to the second fill valve, and the second fill valve is configured to control gas flow from the fill valve to the first grip.

4. The material test system as defined in claim 3 , wherein the processor is configured to control the second fill valve to selectively increase pressure, maintain pressure, or relieve pressure via an exhaust.

5. The material test system as defined in claim 3 , further comprising a third fill valve configured to control gas flow from the fill valve to the second grip.

6. The material test system as defined in claim 3 , wherein the processor is configured to allow the supplied pressure to stabilize after each increase by closing the fill valve and the second fill valve.

7. The material test system as defined in claim 1 , further comprising a dump valve configured to exhaust pressure from the pneumatic grip.

8. The material test system as defined in claim 1 , wherein the fill valve comprises a first solenoid and the dump valve comprises a second solenoid, and the processor is configured to control the first solenoid and the second solenoid to have default states configured to relieve pressure from the pneumatic grip.

9. The material test system as defined in claim 1 , wherein the processor is configured to determine that the supplied pressure has stabilized during the fill cycle based on a rate of change of the pressure.

10. The material test system as defined in claim 9 , wherein the processor is configured to determine that the supplied pressure has stabilized during the fill cycle when the rate of change of the pressure is less than a threshold rate.

11. A method to control a pneumatic device on a material testing system, the method comprising:

controlling, with a processor, a pressure supplied to a pneumatic device of a material testing system during a pressurization of the pneumatic grip over a plurality of fill cycles by repeatedly, via the processor:

in response to determining that a current pressure is less than a target pressure for the pressurization, performing one of the plurality of fill cycles by controlling a fill valve to increase the supplied pressure;

allowing the supplied pressure to stabilize by switching the fill valve to a hold state for a wait time after the fill cycle; and

adjusting the wait time based on comparing an expected pressure increase to an actual pressure increase during a prior one of the fill cycles.

12. The method as defined in claim 11 , wherein the pneumatic grip comprises a first grip and a second grip, wherein the controlling of the pressure supplied to the pneumatic grip comprises controlling the pressure to at least one of the first grip or the second grip.

13. The method as defined in claim 12 , wherein the controlling of the fill valve to increase the supplied pressure comprises:

controlling gas flow from a gas supply to a second fill valve; and

controlling the second fill valve to control gas flow from the fill valve to the first grip.

14. The method as defined in claim 13 , further comprising controlling the second fill valve to selectively increase pressure, maintain pressure, or relieve pressure via an exhaust.

15. The method as defined in claim 13 , wherein the controlling of the fill valve to increase the supplied pressure comprises controlling gas flow from the fill valve to the second grip by controlling a third fill valve.

16. The method as defined in claim 13 , wherein the allowing of the supplied pressure to stabilize comprises closing the fill valve and the second fill valve.

17. The method as defined in claim 11 , further comprising controlling a dump valve to exhaust pressure from the pneumatic grip.

18. The method as defined in claim 11 , wherein the fill valve comprises a first solenoid and the dump valve comprises a second solenoid, the method further comprising controlling the first solenoid and the second solenoid to have default states configured to relieve pressure from the pneumatic grip.

19. The method as defined in claim 11 , further comprising determining that the supplied pressure has stabilized during the fill cycle based on a rate of change of the pressure.

20. The method as defined in claim 19 , wherein the determining that the supplied pressure has stabilized during the fill cycle is in response to determining that the rate of change of the pressure is less than a threshold rate.

21. The material testing system as defined in claim 1 , wherein the processor is further configured to, for at least one of the plurality of fill cycles, control an air pressure filling parameter of the at least one of the fill cycles based on comparing the expected pressure increase to the actual pressure increase during the prior one of the fill cycles.